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An Integrated Approach to Reduce Peel Breakdown in Fresh Citrus

Permanent Link: http://ufdc.ufl.edu/UFE0042272/00001

Material Information

Title: An Integrated Approach to Reduce Peel Breakdown in Fresh Citrus
Physical Description: 1 online resource (79 p.)
Language: english
Creator: Sambhav, Sambhav
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: citrus, peel, postharvest, preharvest
Horticultural Science -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS SAMBHAV August 2010 Chair: Mark A. Ritenour Major: Horticultural Science Florida is the largest producer of citrus in the U.S.A., especially oranges for the juice market and grapefruit for the fresh market. Peel breakdown of fresh fruit usually manifests itself after packing and shipping and can result in major economic losses. Unusually severe peel breakdown problems were reported during the 2006-07 and 2007-08 fresh citrus seasons. Plots were established from 2007 to 2010 in commercial groves using standard fresh fruit growing practices to evaluate the effects of foliar nutritional sprays and water stress on peel breakdown of fresh citrus. Mono-potassium phosphate (MKP) was applied at 10.65 Kg MKP per acre (0-52-34; 3.62 Kg K2O per acre) with 1.81 Kg per acre low-biuret urea (46-0-0), magnesium (Mg) was applied at 6% (4.53 Kg Epsom salts / 75.70 liters), MKP + Mg was applied separately as two tank mixtures, or an antitranspirant (Vapor Gardregistered trademark) was applied at concentrations of 1% and 2% as whole tree foliar sprays at a rate of 473.17 liters per acre. In addition, whole-tree water stress was induced by withholding water for up to two months before harvest. Fruit samples were harvested at weekly or biweekly intervals and held at ~ 22.7oC and 50-60% RH for three days before washing, coating with carnauba wax and then storing the fruit under ambient conditions. Evaluation of decay and the development of peel disorders and other physiological disorders occurred weekly or biweekly. Tree water stress was measured using a pressure bomb. Incidence of peel breakdown significantly increased after blocking irrigation and rainfall for 49 days before harvest. Foliar applications of K, Mg, K + Mg, or Vapor Gardregistered trademark reduced peel breakdown by about an average of 35.63%, 35.22%, 29.94%, and 45.03% respectively compared to the control fruit during the 2008-09 season. This trend continued the following season with reductions from Vapor Gardregistered trademark being more pronounced whereas results from foliar K and Mg were not always significant. For postharvest treatments, fruit were held for 3 days at 21C with 30%, 60%, or 95% RH. Afterwards, fruit were washed, and either left unwaxed, waxed, or coated with wax containing a fungicide (thiabendazole or Imazalil). Significant difference in total peel breakdown of different relative humidity treatments was observed among treatments with some consistent trends. Waxed fruits, which were kept at 30% RH in prestorage showed approximately eight times and five times more peel breakdown than fruits kept at 60% RH in prestorage after 25 and 45 days of storage respectively. This trend was observed over repeated experiments. Interestingly, in some experiments, adding 2,000 ppm of fungicide Imazalil reduced postharvest peel breakdown.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Sambhav Sambhav.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Ritenour, Mark A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042272:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042272/00001

Material Information

Title: An Integrated Approach to Reduce Peel Breakdown in Fresh Citrus
Physical Description: 1 online resource (79 p.)
Language: english
Creator: Sambhav, Sambhav
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: citrus, peel, postharvest, preharvest
Horticultural Science -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS SAMBHAV August 2010 Chair: Mark A. Ritenour Major: Horticultural Science Florida is the largest producer of citrus in the U.S.A., especially oranges for the juice market and grapefruit for the fresh market. Peel breakdown of fresh fruit usually manifests itself after packing and shipping and can result in major economic losses. Unusually severe peel breakdown problems were reported during the 2006-07 and 2007-08 fresh citrus seasons. Plots were established from 2007 to 2010 in commercial groves using standard fresh fruit growing practices to evaluate the effects of foliar nutritional sprays and water stress on peel breakdown of fresh citrus. Mono-potassium phosphate (MKP) was applied at 10.65 Kg MKP per acre (0-52-34; 3.62 Kg K2O per acre) with 1.81 Kg per acre low-biuret urea (46-0-0), magnesium (Mg) was applied at 6% (4.53 Kg Epsom salts / 75.70 liters), MKP + Mg was applied separately as two tank mixtures, or an antitranspirant (Vapor Gardregistered trademark) was applied at concentrations of 1% and 2% as whole tree foliar sprays at a rate of 473.17 liters per acre. In addition, whole-tree water stress was induced by withholding water for up to two months before harvest. Fruit samples were harvested at weekly or biweekly intervals and held at ~ 22.7oC and 50-60% RH for three days before washing, coating with carnauba wax and then storing the fruit under ambient conditions. Evaluation of decay and the development of peel disorders and other physiological disorders occurred weekly or biweekly. Tree water stress was measured using a pressure bomb. Incidence of peel breakdown significantly increased after blocking irrigation and rainfall for 49 days before harvest. Foliar applications of K, Mg, K + Mg, or Vapor Gardregistered trademark reduced peel breakdown by about an average of 35.63%, 35.22%, 29.94%, and 45.03% respectively compared to the control fruit during the 2008-09 season. This trend continued the following season with reductions from Vapor Gardregistered trademark being more pronounced whereas results from foliar K and Mg were not always significant. For postharvest treatments, fruit were held for 3 days at 21C with 30%, 60%, or 95% RH. Afterwards, fruit were washed, and either left unwaxed, waxed, or coated with wax containing a fungicide (thiabendazole or Imazalil). Significant difference in total peel breakdown of different relative humidity treatments was observed among treatments with some consistent trends. Waxed fruits, which were kept at 30% RH in prestorage showed approximately eight times and five times more peel breakdown than fruits kept at 60% RH in prestorage after 25 and 45 days of storage respectively. This trend was observed over repeated experiments. Interestingly, in some experiments, adding 2,000 ppm of fungicide Imazalil reduced postharvest peel breakdown.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Sambhav Sambhav.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Ritenour, Mark A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042272:00001


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AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS


By

SAMBHAV














A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2010



























2010SAMBHAV































To my family and friends who do not have anything to do with this but I just love them









ACKNOWLEDGMENTS

I thank my adviser Dr. Mark Ritenour, who has always been there to listen to me

and give his invaluable suggestions in research as well as other aspects of life. He has

been a major influence in my life for the last two years, which I feel has made me a

better human being. I couldn't have asked for a better adviser.

I am greatly indebted to all the awesome people in my lab: Cuifeng Hu, Monty

Myers, Jordan Yancy, Kendra Thomason, Kayla Thomason and Andrew Myers for their

unwavering support and assistance.I thank the members of my supervisory committee,

Dr. Steve Sargent and Dr. Greg McCollum for all their assistance and insight on this

project.









TABLE OF CONTENTS

page

A C K N O W LED G M ENTS ......... ................... ........... .. ......................................... 4

LIST OF TABLES ........... .... .... ..... ..................... ....... ............... 7

LIS T O F F IG U R E S .................................................................. 9

ABSTRACT ........... ....... .................................... ............... 10

1 INTRODUCTION ...................................................................... ......... ................... 12

Taxonom y, O rigin and History ........................................ 12
Production..................... ...................................... 12
Quality of Florida Citrus ........... ......... ........................... 14
Harvest Operations ...... ............... ..................... .............................. 15
Postharvest Operations ........ ......... ............................ 15
Maintaining Postharvest Quality ........................ ..... .......... ........... 15
Citrus Quality Problems in Florida ............... ......................... ............ 17
Citrus Peel and Peel Breakdown ............... ........................ ............. 17
Pre-harvest Peel Disorders ...... .... ... ..... ................................... 18
Nutritional or spray damage disorders .................................................. 18
Weather related disorders .................. ..................... 19
Maturity related disorders ............................. ......... .. .. ........... 20
Harvest Related Disorders ...... ............. .................. ......... 21
Postharvest Related Disorders .............................................. 21

2 PREHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF CITRUS ...... 32

Introduction .............. ................................................ 32
Materials and Methods............................. ............ ............... 34
F ru it ..................................................................................................... 3 4
E x p e rim e nt 1 ..................................................................... 36
Experiment 2 ........................................................................... ......... ................... 36
Experiment 3 ........................................................................... ......... ................... 36
Experiment 4 ........................................................................... ......... ................... 37
Experiment 5 ......................................................................................................... 37
Fruit Quality Parameters................................ .................... 37
Peel color................................. ........................ 37
Peel puncture resistance .................. .................... 38
Soluble solids content and titratable acidity .......... ..... ................ 38
Percent juice ........... ......... .................... ......... 38
Statistical analysis................................... ............ ............... 38
Results and Discussion.......................................... ............... 39
E x p e rim e nt 1 ..................................................................... 3 9
Experiment 2 ........................................................................... ......... ................... 40









Experiment 3 ........................................................................... ......... ................... 41
Experiment 4 ........................................................................... ......... ................... 42
Experiment 5 ........................................................................... ......... ................... 44

3 POSTHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF WHITE
GRAPEFRUIT.............................................. 45

Introduction .............. ........................... ....... ...... ................................... 45
Materials and Methods........................................... ............... 46
F ru it ......................................... .......... ...... 4 6
Humidity Treatments ....................... ......... ............... 46
Decay and Peel Breakdown .................. ........................... 47
Weight Loss.................................. ............... 47
S tatistica l A na lysis ........................................................................ ......... 4 8
Results and Discussion.......................................... ............... 48

4 EFFECT OF DIFFERENT COATINGS ON REDUCING FREEZE INJURY OF
W H ITE G RA PEFR U IT ........... ........ ......... .......... ............... ............. .. 59

Introduction ...................... ......... ............... 59
Materials and Methods........................................... ............... 60
F ruit ........................................................................... 60
Harvest and Postharvest Operation:. ............. ....... ........................ ...... 61
W eight Loss............................................. ............... 61
S tatistica l A na lysis ........................................................................ ......... 62
Results and Discussion......... ................ ................ 62

5 C O N C LU S IO N .......................................... ................. ............... 70

LIST OF REFERENCES ................................. ............... 72

BIO G RA PHICAL SKETCH ........... .......... .............................. ............... 79



















6









LIST OF TABLES


Table page

1-1 Optimum holding temperatures for maximum quality and shelf life of fresh
Florida citrus fruit ......... ............... ........................................... .............. 16

1-2 Florida Citrus: Production by counties and types, 2008-2009 .......................... 28

2-1 Grove location, citrus type, rootstock used, soil type and age of grove of the
fields where treatm ents were initiated. ............................. .... .......... ......... 34

2-2 Peel breakdown and decay of 'Valencia' oranges after 44 days of storage
under ambient conditions. The fruit were harvested on 10th June, 2009, 2
weeks after treatment application. ............ ...... .... ...... ............... 40

2-3 Peel breakdown and decay of 'Valencia' oranges after 44 days of storage
under ambient conditions. The fruit were harvested on 17th June, 2009, 3
weeks after treatment application. ....................... ................. .............. 40

2-4 Peel breakdown and decay of 'Marsh' white grapefruit after 25 days of
storage under ambient conditions. The fruit were harvested on 19th Feb,
2010, 3 weeks after treatment application. ...................................... 42

2-5 Peel breakdown and decay of 'Marsh' white grapefruit after 63 days of
storage under ambient conditions. The fruit were harvested on 19t Feb,
2010, 3 weeks after treatment application. ............. ...... ................... 42

2-6 Peel breakdown and decay of 'Ruby' red grapefruit after 31 days of storage
under ambient conditions. The fruit were harvested on 05th March, 2010, 1
week after treatment application........................ ........ ............... 43

2-7 Peel breakdown and decay of 'Ruby' red grapefruit after 59 days of storage
under ambient conditions. The fruit were harvested on 05th March, 2010, 1
week after treatment application........................ ........ ............... 44

3-1 Different humidity and packingline treatment given to 'Marsh' white grapefruit
were performed in Vero Beach, Florida on 26th January and 16 February
2 0 0 9 ... ... .......................................... ........ .......... ...... 4 7

3-2 Weight loss in white grapefruit harvested on 26 January after 2, 7, 14 and 21
days of storage at respective relative humidity ........................... ... ............... 56

3-3 Decay (%) of white grapefruit harvested on 26 January after 24 days of
s to ra g e .......................................................... ..................................... 5 7

3-4 Decay (%) of white grapefruit harvested on 26 January after 52 days of
storage. ............................................. 57









3-5 Decay (%) of white grapefruit harvested on 16thFebruary after 25 days of
storage. ............................................. 58

3-6 Decay (%) of white grapefruit harvested on 16thFebruary after 45 days of
storage. ............................................. 58

4-2 Fruit drop and tree injury of the Fort Pierce block evaluated on 08February,
2 0 10 ........... ......... .................................. ............................ 6 3









LIST OF FIGURES


Figure page

1-1 Major Citrus producing counties in Florida ................................... ................ 28

1-2 Postharvest pitting in grapefruit. .................................................. 29

1-3 Stem end rind breakdown in grapefruit ...... ............... ........ ........ 30

1-4 W ind scarring of grapefruit ............ ... ......... ........................ 30

1-5 O leocellosis on grapefruit. ........................... .................. ..... .......... 31

3-1 Total peel breakdown (%) of white grapefruit harvested on 16February after
25 days of storage ...... ...... ........... .............. ............... 53

3-2 Total peel breakdown (%) of white grapefruit harvested on 16 February after
45 days of storage ............ .. ... ........ .. ........... .................. ........ ......... 54

3-3 Total peel breakdown (%) of white grapefruit harvested on 26 January after
24 days of storage ................. ....... .. ........... ........................... ........ 55

3-4 Total peel breakdown (%) of white grapefruit harvested on 26 January after
52 days of storage ............ ..... ....... .. ........... ........................... ........ 56

4-1 Temperature and RH data from the data logger at Fort Pierce block in the
week of harvest from 01/06/10 to 01/14/10. ......... .............. ...................... 64

4-2 Temperature and RH data from the data logger at Vero block in the week of
harvest from 01/06/10 to 01/14/10. ...... ................. ................................. 65

4-3 Freeze injury (Number 9 on the freezing scale)............ .... .......... ................ 66

4-4 Freeze injury (Number 8 on the freezing scale)............ .... .......... ................ 66

4-5 Freeze injury (Number 7 on the freezing scale)............ .... .......... ................ 67

4-6 Freeze injury (Number 5 on the freezing scale)............ .... .......... ................ 67

4-7 Freeze injury (Number 4 on the freezing scale)............ .... .......... ................ 68

4-8 Freeze injury (Number 3 on the freezing scale)............ .... .......... ................ 68









ABSTRACT OF THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS

By

SAMBHAV

August 2010
Chair: Mark A. Ritenour
Major: Horticultural Science

Florida is the largest producer of citrus in the U.S.A., especially oranges for the

juice market and grapefruit for the fresh market. Peel breakdown of fresh fruit usually

manifests itself after packing and shipping and can result in major economic losses.

Unusually severe peel breakdown problems were reported during the 2006-07 and

2007-08 fresh citrus seasons. Plots were established from 2007 to 2010 in commercial

groves using standard fresh fruit growing practices to evaluate the effects of foliar

nutritional sprays and water stress on peel breakdown of fresh citrus. Mono-potassium

phosphate (MKP) was applied at 10.65 Kg MKP per acre (0-52-34; 3.62 Kg K20 per

acre) with 1.81 Kg per acre low-biuret urea (46-0-0), magnesium (Mg) was applied at

6% (4.53 Kg Epsom salts / 75.70 liters), MKP + Mg was applied separately as two tank

mixtures, or an antitranspirant (Vapor Gard) was applied at concentrations of 1% and

2% as whole tree foliar sprays at a rate of 473.17 liters per acre. In addition, whole-tree

water stress was induced by withholding water for up to two months before harvest.

Fruit samples were harvested at weekly or biweekly intervals and held at ~ 22.70C and

50-60% RH for three days before washing, coating with carnauba wax and then storing

the fruit under ambient conditions. Evaluation of decay and the development of peel

disorders and other physiological disorders occurred weekly or biweekly. Tree water









stress was measured using a pressure bomb. Incidence of peel breakdown significantly

increased after blocking irrigation and rainfall for 49 days before harvest. Foliar

applications of K, Mg, K + Mg, or Vapor Gard reduced peel breakdown by about an

average of 35.63%, 35.22%, 29.94%, and 45.03% respectively compared to the control

fruit during the 2008-09 season. This trend continued the following season with

reductions from Vapor Gard being more pronounced whereas results from foliar K and

Mg were not always significant.

For postharvest treatments, fruit were held for 3 days at 210C with 30%, 60%, or

95% RH. Afterwards, fruit were washed, and either left unwaxed, waxed, or coated with

wax containing a fungicide (thiabendazole or Imazalil). Significant difference in total peel

breakdown of different relative humidity treatments was observed among treatments

with some consistent trends. Waxed fruits, which were kept at 30% RH in prestorage

showed approximately eight times and five times more peel breakdown than fruits kept

at 60% RH in prestorage after 25 and 45 days of storage respectively. This trend was

observed over repeated experiments. Interestingly, in some experiments, adding 2,000

ppm of fungicide Imazalil reduced postharvest peel breakdown.









CHAPTER 1
INTRODUCTION

Taxonomy, Origin and History

The genus Citrus belongs to the Rutaceae family, sub-family Aurantioideae.

Sweet oranges probably arose in India, the trifoliate orange and mandarin in China and

acid citrus types in Malaysia.

Citrus was probably introduced in Florida by explorer Ponce de Leon's when he

brought citrus seeds to Florida in 1493(Michael, 2000). Citrus culture proliferated in

Florida in the late 1700's, when the first commercial shipments were made. By the

1999-2000 season, Florida's citrus industry was one of the largest sources of income

and employment in Florida with an overall economic impact of $9 billion, $4 billion in

value added, and employed 89,700 people (Hodges et al., 2001). Fresh Florida citrus

had an overall economic impact of $1 billion and employed 17,471 in 1999-2000

season. Thus, research that improves the quality of fresh citrus is economically

important to the state of Florida.

Florida's citrus industry had an economic impact of $9 billion in industry output, $4

billion in value added, and 89,700 jobs in 1999-2000 season (Hodges et al., 2001).

Fresh Florida citrus accounted for $1 billion in industry output with 17,471 jobs added in

1999-2000 season. Thus, research that improves the quality of fresh citrus is relevant to

the state of Florida.

Production

Florida's citrus industry is the largest producer of citrus in the United States of

America. Seventy one percent of total U.S. citrus production in the 2008-09 season was

from Florida with orange and grapefruit production at 162 million boxes and 21.7 million









boxes respectively. There is a total of 530,900 acres of bearing citrus acres, which is

down from the maximum of 941,471 acres in 1970 (Citrus summary, 2002 and 2009).

Major citrus growing regions are in South Florida with Polk, Hendry, Highlands and

Desoto counties being the top four producers representing 50% of the state's total citrus

production. (Table 1-2 and Figure 1-1) (Citrus summary, 2009). The four counties

combined accounted for over 55% of the State's total orange production. Indian River

and St. Lucie counties produced almost 2/3 of the State's grapefruit crop (Citrus

summary, 2009). Four percent of Florida oranges go to the fresh market while 43% of

Florida grapefruit goes to fresh market. The Indian River Research and Education

Center in Fort Pierce is located in the heart of this fresh grapefruit growing region and is

strategically located in close contact with citrus growers and packers.

All citrus are small, spreading, evergreen trees or tall shrubs. Plantings are usually

in rectangular arrangements which eventually become tall hedgerows. Spacings are

typically 20 x 25m for grapefruit and vigorous trees, 15 x 20m for oranges and

tangerines, and 12-15m x 18-20m for limes and smaller cultivars. Tree densities are

about 100-110 trees/acre for grapefruit, and 130-140 for sweet orange. Very little

training is needed for citrus but the trees are pruned at regular intervals. Citrus trees are

generally budded onto various rootstocks, which are chosen based on rootstock's

horticultural traits like yield, resistance to pests and diseases or tolerance to soil type.

Drip irrigation is primarily used to supply water and fertilizer (Tucker, 1978). Over 97%

of Florida citrus is irrigated. Micro-irrigation methods are used on over 67% of irrigated

citrus groves (Marella, 1995).









Quality of Florida Citrus

Florida citrus is known all over the world for its quality. Florida citrus has different

quality factors for the fresh and processing markets. For juice, the most important

quality factors include fruit juice content, fruit size, color, soluble solids and acid

concentrations and soluble solids-acid ratio. In addition to internal quality, fruit size,

shape, color and maturity date are important for fresh fruit. 'Ruby Red', 'Flame' and

'Marsh' are important grapefruit varieties, 'Hamlin' and 'Navel' are important orange

varieties, and 'Sunburst', 'Honey' and 'Fallglo' are important varieties of mandarin.

Grapefruit, navel oranges, tangerines, and mandarin hybrids fetch relatively high

economic returns as fresh fruit, but low returns when they are diverted for the juice

market because of poor external quality (i.e., peel blemishes) (Stelinski et al., 2009).

Florida citrus is known all over the world for its quality. It is used both for fresh

market as well as for extracting juice. Juice is particularly of high quality. The most

important quality factors include fruit juice content, fruit size, color, soluble solids and

acid concentrations and soluble solids-acid ratio. Florida citrus growers have different

quality factors for the fresh and processing markets. Fruit size, shape, color and

maturity date are most important for fresh fruit but high juice content and soluble solids

are important for fruits used in processing. 'Ruby Red', 'Flame' and 'Marsh' are

important varieties of grapefruit. 'Hamlin' and 'Navel' are important varieties of orange.

'Sunburst', 'Honey' and 'Fallglo' are important varieties of mandarin. Grapefruit, navel

oranges, tangerines, and mandarin hybrids fetch higher value in fresh market and

relatively lower value in processing market (Stelinski et al., 2009).









Harvest Operations

All citrus are non-climacteric fruit; they mature gradually over weeks or months

and are slow to abscise from the tree. Hence, they store best on the tree for most of the

season. External color changes during maturation, but it is a poor indicator of maturity.

The best indices of citrus maturity are internal: total soluble solids, acid content, and the

total soluble solids/acid ratio (Kader, 1999). For example, a high quality fresh-market

grapefruit will be elliptical and firm, relatively blemish-free with a turgid, smooth peel

(Soule and Grierson, 1986). The fruit will have an appropriate balance of soluble solids:

titratable acidity with minimum bitterness.

The harvesting season for Florida citrus is usually from September June.

Grapefruit availability is throughout the season whereas different varieties of orange

span the season. Specialty fruits like temples, k-early Citrus, tangelos and tangerines

are available for shorter periods during the season. Citrus is harvested both

mechanically and manually in Florida. However, all fresh citrus is harvested by hand

using ladders, bags, bins, conventional fruit loading trucks or "goats" and flat-bed trucks.

Postharvest Operations

Citrus fruits are transported to packinghouses, where they are handled differently

depending on their intended use. Standard packing line operations include dumping

onto the packing line, culling, pre-sizing, washing, drying, grading, waxing, drying, final

grade, sizing, and packing into approved containers.

Maintaining Postharvest Quality

Cultivar, environmental conditions, and postharvest handling practices are

important factors in determining postharvest quality. Cultivar selection is important in

addressing postharvest quality issues such as firmness, because most of these are









genetically controlled (Prange and DeEII, 1997). Environmental conditions can influence

postharvest quality in citrus and other commodities (Kader, 2002; Prange and DeEII,

1997). Fruit size is an important factor of quality for fresh citrus consumption (Agusti,

1999). Optimum storage temperature of citrus ranges from 0 to 150C depending on

citrus variety and time of year (Table 1-1). Kumquats and mandarins are the most cold

tolerant whereas Limes and citrons are the least (Ladaniya, 2008). Early season, un-

waxed grapefruit should be shipped at 15C to avoid chilling injury (Ritenour et al.,

2003). Later in the season, temperature can be reduced to 12C and then to 10C. Late

season grapefruit should be handled at 15 C as it may become susceptible to chilling

injury and decay. Depending on the gas diffusion of a particular wax formulation,

waxed citrus can be held at lower temperatures without developing chilling injury

compared to non-waxed fruit. Postharvest handling also influences the quality of a

commodity. For optimum quality and quality retention during postharvest handling, fresh

citrus must also be harvested at the correct maturity stage. For example, postharvest

physiological disorders are more likely in fruits picked too early or too late in their

season than in fruits picked at their optimum maturity (Kader, 1999).

Table 1-1. Optimum holding temperatures for maximum quality and shelf life of fresh
Florida citrus fruit
Citrus type Optimum holding temperature (0 C)
Oranges 0-1

Mandarin-type fruits 4

Lemon, Limes 10

Grapefruit 10-15









Citrus Quality Problems in Florida

Citrus quality in Florida can be negatively affected by many disorders, making it

unacceptable for the fresh market. When the fruit is not suitable for the fresh market, it

is consigned for juice purposes, which leads to less profit to the grower. It is a much

worse situation if the disorder develops during shipment, which results in rejection at the

destination. This leads to higher losses as the cost of shipping is also incurred. In

addition, when the buyer receives such fruit, they are less inclined to purchase fruit from

that shipper again. Among the diseases and disorders that render citrus fruit unsuitable

for the fresh market are 1) physical injuries such as cuts and punctures, 2) infestation

with pests such as the Caribbean fruit fly, 3) pathological disorders resulting in decay or

peel blemishes (i.e., from melanose, canker, etc.), and 4) physiological disorders such

as stem-end rind breakdown or chilling injury.

Citrus Peel and Peel Breakdown

The citrus rind consists of the flavedo and albedo. The flavedo comprises the

outermost part of the rind and includes the cuticle, epidermal cells, sub epidermal cells

and oil glands (Schneider, 1968). The albedo comprises the internal spongy white part

of the peel and primarily contains parenchyma cells interspread with vascular bundles.

Peel disorders severely degrades the fruit appearance, but usually do not affect the

edible or nutritive quality of the fruit (Petracek et al., 2006). In addition, peel disorders

predispose the fruit to invasion by decay organisms, thus reducing postharvest shelf life

(Hopkins and McCornack, 1960; McCornack, 1973; Smoot, 1977; Schiffmann-Nadel et

al., 1975). Peel disorders are difficult to study for several reasons: they can appear and

disappear unpredictably and a single disorder can have multiple symptoms while

multiple disorders may have similar symptoms, even in the same fruit. Unlike diseases,









which can be positively identified by isolating the causal pathogenic organisms, there

are typically no single factors that critically define a disorder (Petracek et al., 2006).

Hence, it is often difficult to diagnose physiological disorders. Most peel disorders such

as chilling injury, postharvest pitting, oleocellosis, and zebra skin start in the flavedo but

some such as creasing originate in the albedo. Peel disorders can be classified as

preharvest, harvest or postharvest disorders based on their time of appearance.

Pre-harvest Peel Disorders

Preharvest peel disorders can be classified as nutritional, spray damage, weather,

or maturity related depending on the cause of the disorder.

Nutritional or spray damage disorders

Aging and stem end rind breakdown: Detailed information on this disorder is

given in the postharvest section of this chapter.


Boron deficiency: As the name suggests, this disorder is caused by boron

deficiency. Symptoms include raised bumps on the fruit surface and gummy

pockets in the albedo that are visible when the fruit is cut open (Bryan 1950;

Browning et al., 1995).


Pineapple pitting: Pineapple oranges are more susceptible to this disorder than

other citrus varieties. Low potassium levels in adjacent leaves is the main cause

(Grierson, 1965).Symptoms include the collapse of small areas of the flavedo

around the shoulder and cheek of the orange peel. Darkening and coalesce of

pitted areas may be seen (Browning et al., 1995; Smoot et al., 1971).









Spray damage: The main causes of this disorder are incompatible tank mix

chemical combinations, incorrect application rates or timings or a phytotoxic

active ingredient in the mixture (Albrigo and Grosser, 1996). Main symptoms are

streaks of damaged or non degreened cells running longitudinally down the fruit

surface or by rings at fruit to fruit or leaf to fruit contact points.


Ammoniation: Ammoniation is observed when nitrogen is used in excess on

copper deficient soil (Browning et al., 1995; Smoot et al., 1971). Main symptoms

are black or brown raised lesions on fruit.


Weather related disorders

Aging and stem end rind breakdown: Detailed information on this disorder is

given in the postharvest section of this chapter.


Freeze injury: Exposure to low enough temperatures in the field that results in ice

formation within the fruit is the cause for this injury. Symptoms of freezing injury

are internal drying and free juice in the core of fruit. Externally, a pinkish pitting

may develop. Even lighter frost injury in the grove may predispose grapefruit to

alternaria stem-end rot during storage (Schiffmann-Nadel et al., 1975).


Sunburn: Temperature of 44.40 C and 20% relative humidity has been shown to

cause sunburn to 'Valencia' (Ketchie and Ballard, 1968). The typical symptoms

are flat, pale, leathery areas on the exposed side of fruit (Smoot et al., 1971).


Water spot: Water soaking and swelling of the rind around the stylar end is

observed in this disorder. It is a typical problem of Navel oranges produced under









low humidity conditions that are then subjected to a cool, wet period (Scott and

baker, 1947; Klotz, 1975; Riehl and Carman, 1953; Smoot et al., 1971).


*Wind scarring: It is a problem in areas where high wind velocity coincides with

post bloom period. Small (less than 1 cm in diameter) citrus fruits are so

susceptible to abrasion injury that just rubbing against a leaf can cause lesions

that expand to large silvery or tan blemishes as the fruit enlarges (Figure 1-4)

(Elmer et al., 1973; Freeman, 1976; Smoot et al., 1971).


Maturity related disorders

Creasing: The exact cause is unknown. Potassium nutrition, rootstock and water

relations are considered to be probable factors (Bar-Akiva, 1975; Embleton et al.,

1971; Grierson, 1965). Main symptoms are grooves or furrows which are

irregularly distributed on the fruit surface (Browning et al., 1995; Smoot et al.,

1971).


Puffiness: It is the separation of peel from the pulp. Advancing fruit maturity, tree

vigor and weather (particularly irregular water supply) are the main factors

involved in this disorder (Grossenbacher, 1941; Kuraoka, 1962).


Rind staining of navel oranges: It occurs when the peel is so physiologically over

mature that epidermal wax softens and handling causes reddish brown

blemishes (Eaks, 1964). Brownish discoloration of the rind surface is the

characteristic symptom. The susceptibility is increased by ethylene exposure,

use of certain rootstocks such as Rubidox sour and rough lemon, and in trees

having high nitrogen fertilization (Eaks, 1969).









Harvest Related Disorders

Blossom end clearing of grapefruit: Rough handling of late season fruit during

warm temperatures is the primary cause of this disorder. It is characterized by

the translucent, water soaked appearance of the fruit peel (most commonly at the

blossom end) caused by internal bruising and juice leakage from juice vesicles

(McCornack, 1966).


Oleocellosis: It is breaking of oil cells, causing the oil to extrude which damages

the surrounding tissues. Symptoms include discrete spots on the peel, large

scalded areas, and concentric rings of small lesions (Figure 1-5) (Turrell et al.,

1964). The main cause of this disorder is rough handling of very turgid fruit

(Eaks, 1969; Smoot et al., 1971; Nel et al., 1974; Wardowski et al., 1976).


Red colored lesions: These develop when superficial wounds, no deeper than

the flavedo, develop a reddish color in the lesions and surrounding peel. It is

attributed to a reaction in peel tissue that forms compounds that impart

resistance to infection by Pennicillium digitatum (Kavanagh and Wood, 1967).


Postharvest Related Disorders

Aging and stem end rind breakdown (SERB): Symptoms involve the collapse and

subsequent darkening of epidermal tissues, particularly around the stem end of

citrus fruit. A narrow 2 to 5 mm ring of undamaged tissue immediately around the

calyx is a characteristic symptom of SERB (Figure 1-3). Aging of oranges and

grapefruit which can occur after long term storage is almost indistinguishable

from SERB, except that the characteristic narrow ring of healthy cells does not









tend to persist around the calyx (Smoot et al., 1971).SERB is most severe on

oranges and Temples, but it may also occur on tangelos and grapefruit. Small

and well-colored fruit are most susceptible to this disorder. The humid

environment of Florida makes the thinner-skinned fruit more prone to SERB than

thicker-skinned fruit from drier, Mediterranean environments. Fruits affected with

this disorder are more prone to decay during postharvest handling and

marketing. The exact cause of SERB is uncertain. It is primarily associated with

drying conditions. These drying conditions are due to factors such as delays in

packing, holding fruit under low humidity and high temperatures, and excessive

air movement around the fruit (McCornack and Grierson, 1965). Nutritional

imbalances involving nitrogen and potassium can also be a cause (Chapman,

1958).


SChilling injury (CI): It is a common disorder characterized by the collapse of

discrete areas of peel that form sunken lesions which tend to coalesce. It is

induced by low temperature i.e. below 100 C storage (Chace et al., 1966). At very

low temperatures, superficial scalding may occur instead of pitting. It is typically

reddish or tan colored. Browning of the albedo and of carpellary membranes is

peculiar to lemons. In grapefruit and tangelos, oil glands may darken (Smoot et

al., 1971). In Florida, grapefruit are most susceptible to CI early (October-

December) and late (March-May) in the season. The fruit usually become more

resistant to CI during mid-season (December-March). Postharvest temperature

treatments have been used to prevent CI. Intermittent warming throughout the

storage period, stepwise lowering of temperature, and pre-storage heat









treatments can mitigate CI (Davis and Hoffman, 1973). Delayed storage and

storage at high relative humidity can lower the incidence of CI (Pantastacio et al.,

1966). Very high initial concentrations of CO2 can mitigate CI (Brooks et al.,

1936; Vakis et al., 1970; Hatton et al.,1975). Methyl jasmonate (Meir et al., 1996)

and squalene treatment (Nordby and McDonald, 1990) have shown some

protection from CI.


* Drench phytotoxicity: Long term, unmonitored use of drench solution can lead to

the accumulation of chemicals including salts, pre-harvest agro chemicals

washed from the fruit, and even motor oil from truck drenches. If these chemicals

reach phytotoxic concentrations, peel damage will occur. Symptoms include

discolored circular and streaking patterns. The disorder may be called Green

Ring due to characteristic green circles at fruit contact points with other fruit and

bin surfaces that are evident after degreening (Ritenour and Dou, 2000).


* Postharvest pitting: It is characterized by clusters of collapsed oil glands

scattered over the fruit surface (Figure 1-2) (Petracek and Davis, 2000).

Application of waxes with low gas transmission rates exacerbates the disorder

(Petracek et al., 1998). Symptoms of postharvest pitting may also arise after

exposure to low (i.e., 30%) relative humidity environments after harvest, but it is

unclear these disorders share a common fundamental mechanism (Alferez and

Zacarias, 2001).


* Rind staining of navelina oranges: It is characterized by collapse and drying of

flavedo and eventually by darkening of affected area over time (Laufente and









Sala, 2002). It is observed mainly in navel oranges. It is both a pre- and

postharvest disorder. Rind staining occurs at the stage when the peel is

physiologically over mature and epidermal wax softens. Hence, handling causes

reddish-brown blemishes (Eaks, 1964). Ethylene treatment, high rates of nitrogen

fertilization and root stocks that promote vigorous growth make fruit susceptible

to this disorder.


Peel breakdown problems were severe during the 2006-07 and 2007-08

seasons in Florida. According to industry estimates, these two seasons has cost

the fresh citrus industry as much as $1 million in claims both years. These

breakdown problems were not associated with chilling injury (Petracek et al.,

1995). The common disorders observed in this study were general peel

breakdown and SERB. Symptoms included areas of peel pitting and necrosis

that appeared during the winter months, especially after cool and/or windy

weather, and progressed into the spring as stem-end rind breakdown (Ritenour

and Dou, 2003) when trees were flushing/flowering and temperatures were

warming. The occurrence of peel breakdown of 'Fortune' mandarin under cool

and low relative humidity (RH) conditions was also reported (Agusti et al., 1997;

Vercher et al., 1994), but these reports suggested the temperature was cold

enough to cause CI. As previously stated, CI was not likely the cause of the

Florida peel disorder. Recent studies in Florida have shown that sudden changes

in relative humidity (RH; e.g., from 30% to 90%) after harvest can cause peel

pitting of Florida citrus that is not related to CI (Alferez and Burns, 2004; Alferez

et al., 2005).Of the preharvest factors, plant nutrition imbalance concerning









potassium and nitrogen and water stress have been suggested as potential

factors influencing the susceptibility of citrus fruit to postharvest peel breakdown

(Alferez et al., 2005; Grierson, 1965). For example, SERB has been reported by

some to be more severe when fruit are harvested from water-stressed trees

compared to non-stressed trees, whereas others have found no significant

relationship (Grierson, 1965). In addition, researchers in other countries found

that nutritional imbalances involving high N and low K may predispose fruit to

SERB (Chapman, 1958; Grierson, 1965). No conclusive relationship between

plant water stress, low K, high N, and SERB development under Florida

conditions has been demonstrated. Recent research showed reduced peel

breakdown after a preharvest magnesium (Mg) application on 'Nules Clementine'

mandarin in South Africa (Cronje et al., 2008). Improved plant water status was

observed from the emulsions of wax, latex and plastic that dries on the foliage

and forms thin films (Gu et al., 1996; Hummel, 1990; Nitzsche et al., 1991; Plaut

et al., 2004). Foliar application of this emulsion minimized plant water loss by,

decreasing stomatal conductance (gs), and reducing transpirational losses,.

Better appearance and excellent weathering resistance was observed after the

application of polyterpene antitranspirant, pinolene on the orange surface

(Albrigo, 1970). SERB, oleocelosis and creasing can be reduced by using

preharvest antitranspirants spray (Albrigo, 1970).

The current studies were initiated to evaluate various pre- and postharvest

treatments to better understand the factors related to the development and

prevention of postharvest peel breakdown on fresh citrus. Based on the above









information related to the disorder, experiments were designed to test the

hypothesis that postharvest peel breakdown can be reduced by improving plant

nutrition through foliar K, Mg, or K + Mg sprays before harvest, reducing

preharvest water stress of the trees, or by preventing postharvest exposure to

low RH conditions.

The objectives of this study were to evaluate the potential effect of preharvest

plant water stress and foliar K, Mg and antitranspirant applications on

postharvest peel breakdown of fresh Florida citrus (especially grapefruit). In

addition, the effects of holding fruit under different RH conditions after harvest

and the effects of different packingline treatments on peel breakdown were also

evaluated. The goal was to better predict what conditions promote and retard

peel breakdown, and to develop production and postharvest practices to reduce

or eliminate the occurrence of this disorder.










Table 1-2. Florida Citrus: Production by counties and types, 2008-2009
County All Oranges Grapefruit
Citrus Early-mid- Late All White Colored All
Navel-
Temple (Valencia)
1,000 boxes
Brevard 806 381 303 684 25 56 81
Charlotte 3,503 907 1,973 2,880 12 409 421
Collier 10,069 4,290 5,214 9,504 29 383 412
DeSoto 20,639 9,068 11,198 20,266 26 193 219
Glades 3,057 1,598 1,330 2,928 9 34 43
Hardee 15,366 10,463 4,341 14,804 68 197 265
Hendry 21,796 8,274 12,201 20,475 250 723 973
Hernando 294 270 6 276 -6 6
Highlands 23,219 9,670 12,417 22,087 382 358 740
Hillsborough 4,110 2,964 899 3,863 18 33 51
Indian River 11,434 2,320 1,684 4,004 2,751 4,519 7,270
Lake 4,737 2,636 947 3,583 59 476 535
Lee 3,226 1,070 1,786 2,856 19 264 283
Manatee 7,293 4,301 2,724 7,025 64 124 188
Marion 381 266 60 326 3 14 17
Martin 5,309 1,653 3,419 5,072 70 116 186
Okeechobee 2,137 950 787 1,737 110 220 330
Orange 1,359 783 465 1,248 8 36 44
Osceola 3,581 2,113 940 3,053 257 191 448
Palm Beach 237 12 -12 -50 50
Pasco 2,945 2,249 577 2,826 9 37 46
Polk 30,253 16,007 11,145 27,152 705 1,057 1,762
St. Lucie 12,329 1,873 3,175 5,048 1,686 5,386 7,072
Sarasota 439 96 138 234 22 152 174
Seminole 156 100 21 121 -13 13
Volusia 292 192 40 232 16 36 52
Total 189,100 84,600 77,800 162,400 6,600 15,100 21,700






























1 52


60 I


66
I ,
86 yr~~-'-


Figure 1-1.Major Citrus producing counties in Florida. Adapted from USDA, NASS
Citrus summary 2008-09.County no. 46- Polk, County no. 54- Highlands,
County no. 53- Desoto, County no. 62- Hendry and County no. 56- Indian
River County.

































Figure 1-2. Postharvest pitting in grapefruit.































Figure 1-3. Stem end rind breakdown in grapefruit.


Figure 1-4. Wind scarring of grapefruit






















Figure 1-5. Oleocellosis on grapefruit.









CHAPTER 2
PREHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF CITRUS

Introduction

Plant nutrition and water stress have been suggested as potential preharvest

factors influencing the susceptibility of citrus fruit to postharvest peel breakdown

(Alferez et al., 2005; Grierson, 1965). However, results have not been conclusive. For

example, some authors have reported SERB to be more severe when fruit are

harvested from water-stressed trees compared to non-stressed trees, whereas others

have found no significant relationship with water stress (Grierson, 1965). It has also

been found that nutritional imbalances involving high nitrogen (N) and low potassium (K)

may predispose fruit to SERB (Chapman, 1958; Grierson, 1965). While no conclusive

relationship between plant water stress, low K, high N, and SERB development under

Florida conditions has been demonstrated, trends in data taken in 2007-08 season

supported further study and the potential use of alternate application methods.

Potassium nutrition is emerging as potentially a key factor in influencing peel

health of citrus, especially it's interaction with different nutrients or climatic factors (Bar-

Akiva, 1975; Embleton et al., 1971; Grierson, 1965). Fruit-rind K-deficiency was

observed as superficial rind pitting (SRP) in 'Shamouti' oranges (Tamim et al., 2000),

while K-deficiency increased creasing in many mandarin varieties and Valencia orange

(Raber et al., 1997). Foliar-applied potassium has also been found to increase citrus

fruit size, specific fruit components and increased yields in recent studies (Achilea ,

2000; Erner et al., 1993).

Low plant K levels have also been associated with other citrus peel disorders such

as creasing and 'Pineapple' orange peel pitting (Petracek et al., 1995). Increased K









fertilization has been reported to increase fruit size, weight, vitamin C content, and fruit

storage potential (Embelton et al., 1975). Though high levels of K fertilization may have

some negative effects, such as decrease sugar to acid ratio and color development,

foliar K applications have been reported to increase size without decreasing sugar to

acid ratios, total soluble solids (TSS), acid or juice contents and with no increase in peel

thickness (Boman, 1997; Boman and Hebb, 1998). Imbalances between N and K have

also been reported to affect peel breakdown in citrus (Petracek et al., 1995).Magnesium

(Mg) nutrition was recently reported to reduce peel breakdown of 'Nules Clementine'

mandarin in South Africa (Cronje et al., 2008).

Vapor Gard forms a film on plant tissues and reduces transpiration by 25% to

80% depending on the plant tissue (Davenport et al., 1976, EI-Sharkawy et al., 1976).

Studies showed that antitranspirant application can increase leaf water potential in bell

pepper (Berkowitz and Rabin, 1988; Nitzsche et al., 1991). The emulsions of wax, latex

and plastic that dried on the foliage and formed thin films improved plant water status. It

minimizes transpiration and plant water loss by decreasing stomatal conductance (gs)

(Gu et al., 1996; Hummel, 1990; Nitzsche et al., 1991; Plaut et al., 2004). Better

appearance of fruit and excellent weathering resistance was observed after the

application of a polyterpene antitranspirant, Pinolene on the orange surface topography

(Albrigo et al., 1970). SERB and creasing can be reduced by using preharvest

antitranspirant spray and was, therefore, included in this study.

The objective of the current research was to evaluate the potential effect of plant

water stress and preharvest foliar K, Mg and antitranspirant application on postharvest

peel breakdown of fresh Florida citrus (especially grapefruit).









Materials and Methods


Fruit

'Valencia' oranges, 'Marsh' white grapefruit, 'Sugar Belle' mandarin hybrid and

'Ruby' red grapefruit were used for the different experiments. Trees were located in

commercial citrus blocks and received standard cultural practices used for fresh fruit.

The grove location, citrus type, rootstock used, soil type and age of grove of the fields

where treatment was initiated is followed below (Table 2-1).

Table 2-1. Grove location, citrus type, rootstock used, soil type and age of grove of the
fields where treatments were initiated.
Grove location Citrus type Rootstock used Predominant Age of grove
soil type
Vero Beach 'Valencia' Sour orange Winder fine 25
orange sand
Fort Pierce 'Marsh' white Sour orange Pineda fine 21
grapefruit sand
Fort Pierce 'Marsh' white Cleoparta Wabasso fine 21
grapefruit sand
Vero Beach 'Ruby' red Sour orange Riviera fine 30
grapefruit sand
Vero Beach 'Sugar Belle' Unknown Riviera fine Unknown
mandarin sand
hybrid


For each experiment, whole trees were exposed to different combinations of the

following treatments:

Control unsprayedd trees with normal irrigation).


Foliar applied K (10.6 Kg MKP/acre [0-52-34]; 3.6 Kg K20/acre) with 1.8 Kg per

acre low-biuret urea (46-0-0).


Foliar applied Mg (6% [4.53 Kg Epsom salts /75.7 liters])









Foliar applied K plus Mg. Applied separately as two tank mixtures with the same

concentrations used above.


Foliar applied Vapor Gard (1% = 473.1 liters per acre).


Irrigation deficit (1 month before harvest plugged irrigation jets and Tveyk was

laid around the base of the trees to prevent rain from replenishing soil moisture).


Vapor Gard (2%).


Unless otherwise stated, field plots were established in a randomized complete

block design with 4 replicates of 5 trees each. Foliar treatments were sprayed to all

sides of the tree uniformly at a rate of approximately 473.1 liters/acre. Fruits were

evaluated from middle 3 trees. Fruit were harvested 7, 14, 21, 28 and/or 35 days after

spraying. Fifty fruits were harvested per replicate and brought to Indian River Research

and Education Center at Fort Pierce, Florida on the same day. Fruit were placed on the

postharvest lab floor (~23 OC, 50-60% RH) for 3 or 4 days before washing and waxing.

Ten extra fruits were harvested for internal quality assessment in the 3rd week after

spraying. Fruits were washed and rinsed (without SOPP, chlorine or any other

fungicides) and waxed (carnauba, FMC Corporation). Fruits were then kept under

ambient conditions on the postharvest facility floor (~ 23 OC), conditions thought to

promote peel breakdown. Decay and peel breakdown was visually evaluated on each

fruit and the percentage of fruit showing any decay or peel breakdown was calculated.

Decayed fruits were discarded from the replicate after each week of evaluation.









Experiment 1

Treatments were initiated on 27 May, 2009 in a Vero Beach block of 'Valencia'

oranges. Spraying started at 12 pm and was completed at 2 pm. Wind velocity was less

than 2 meter per second and the air temperature was 340 C. Field treatments included

foliar applications of K, Mg, K plus Mg and 1% Vapor Gard.

Experiment 2

Treatments were initiated on 20 November, 2009 with 'Marsh' white grapefruit in

Fort Pierce, Florida. Spraying started at 10 a.m. Air temperature was 210C and wind

velocity was less than 2 meter per second. Irrigation jets were plugged to stop irrigation

in the respective treatment on the same day. Field treatments included foliar

applications of K, Mg, 1% & 2% Vapor Gard and withholding irrigation rain. Fruit were

harvested 14, 21 and 35 days after treatment. Fruit from the irrigation deficit treatment

were harvested 35 days after treatment initiation. Forty fruits were harvested per

replicate from the experimental site.

Experiment 3

Treatments were initiated on 26 January, 2010 with 'Marsh' white grapefruit in Fort

Pierce, Florida. Spraying was done in the afternoon. Wind velocity was 4 meter per

second. Temperature was 200 C. Field treatments included foliar applications of K, Mg,

1% & 2% Vapor Gard, Foliar K, Mg, & 1 % Vapor guard (applied separately, in that

order), Miller cocktail (Calexin; Millerplex; Greenstim; 1% Vapor Guard) and withholding

irrigation/rain. Field Treatments were done in RCB design with 4 replicates of 3 trees

each. Fruits were evaluated from middle tree. Fruit were harvested after 1, 3, 5 and 7

weeks after treatment. Irrigation deficit treatment fruit were harvested 5 weeks after

treatment. Forty Fruits were harvested per replicate.









Experiment 4

Treatments were initiated on 23 February, 2010 with 'Ruby' red grapefruit in Vero

Beach, Florida. Spraying was done in the afternoon. Wind velocity was approximately 2

miles per hr. Temperature was 250 C. Field treatments included foliar applications of K,

Mg, 1% & 2% Vapor Gard, Foliar K, Mg, & 1 % Vapor guard (applied separately, in

that order) and Miller cocktail (Calexin; Millerplex; Greenstim; 1% Vapor Guard).Field

treatments were done in RCB design with 4 replicates of 3 trees each. Fruits were

evaluated from middle tree. Fruit were harvested after 1 and 3 weeks after treatment.

Forty fruits were harvested per replicate.

Experiment 5

Treatments were initiated on 14 December, 2009 with 'Sugar Bells', a mandarin

hybrid in Vero Beach, Florida. Spraying was done in the afternoon at 3 p.m.

Temperature was 250C and wind speed was 2 meter per second from east to west.

Single tree replicates were used. Field treatments included foliar applications of K and

Mg.- Four reps of 1 tree each were used for treatments. Fruit were harvested after 1, 7

and 21 days after treatment. Sixty Fruits were harvested per replicate.

Fruit Quality Parameters

Peel color

Peel color was measured using a Minolta Chroma Meter (CR-300 series, Minolta

Co. Ltd., Japan) at three equidistant locations on each fruit along the equator of the fruit

and expressed as L*, a* and b* values. The hue and chroma values were calculated

from a* and b* values using the following formulas:

Hue = arc tangent (b*.a*-1)

Chroma = (a*2 + b*2)1/2









Peel puncture resistance

Peel puncture resistance was measured at two equidistant spots along the equator

of each fruit using a texture analyzer (Model TAXT2i, Stable Micro Systems, Godalming,

England) with a 2 mm diameter, flat-tipped, cylindrical probe. The analyzer was set so

the probe traveled at a speed of 2 mm-s1 and the maximum force exerted to puncture

the peel recorded. Peel puncture resistance was expressed in Newtons.

Soluble solids content and titratable acidity

Fruit were cut into halves along the equator and juice was extracted using a test

juice extractor (Model 2700, Brown Citrus Systems Inc., Winter Haven, Fla.). Juice total

soluble solids (TSS) was measured using a temperature-compensated refractometer

(Abbe-3L, Spectronic Instruments Inc., Rochester, N.Y.) and the juice titrable acidity (%

citric acid) was measured by titrating 40 mL of juice samples to pH 8.3 with 0.3125 N

NaOH using an automatic titrimeter (DL 12, Mettler-Toledo Inc., Columbus, Ohio).

Percent juice

Percent juice was calculated from the total weight of fruit and total weight of juice.

Percent juice = Juice weight (g) 100/ Fruit weight (g)

Statistical analysis

Percentage data (peel breakdown, decay) was transformed to arcsine values and

all data were analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS

Institute Inc, Cary, N.C.). When differences were significant (P < 0.05), individual

treatment means were separated using Duncan's multiple range tests (P = 0.05).









Results and Discussion


Experiment 1

There was no significant difference among the treatments for peel color, total

soluble solids and titratable acidity, peel puncture resistance and juice percent (data not

shown here).Foliar applications of K, Mg, K + Mg, and Vapor Gard reduced peel

breakdown by about an average of 35%, 35%, 29%, and 45% respectively compared to

the control fruit. Peel breakdown and fruit decay increased as storage duration

increased. Peel breakdown was much lower in fruit harvested 1 week after field

treatments were administered compared to the other harvests (Table 2-2 and 2-3).This

trend was also observed in other experiments(data not shown here). This coincides with

the previous study done (Ritenour et al., 2008). In the table 2-2, decay and peel

breakdown of 'Valencia' orange is shown. Total peel breakdown is the aggregate of all

types of peel breakdown observed in the fruit. In this experiment, the total peel

breakdown was due to general breakdown and not due to stem end rind breakdown or

other peel disorders. Foliar application of potassium and 1% Vapor Gard reduced peel

breakdown by 50% as compared to control fruit.

In the table 2-3, peel breakdown and decay of 'Valencia' orange is observed after

44 days of storage. These fruits were harvested 3 weeks after treatment application.

Total decay and peel breakdown has increased irrespective of treatment applied in this

week as compared to 2 week after treatment application(table 2-2). Treatment of 1%

Vapor Gard reduced peel breakdown by more than 50% as compared to control fruit.











Table 2-2. Peel breakdown and decay of 'Valencia' oranges after 44 days of storage
under ambient conditions. The fruit were harvested on 10th June, 2009, 2 weeks after
treatment application.
Peel breakdown
Treatment Sound Total decay General Total
Control 47 28 ab 34 a 34 a
1% Vapor Gard 65 27 bc 15 c 15 c
K 60 38 a 14 c 14 c
Mg 65 17 c 22 bc 22 bc
Foliar K + Mg 56 27 bc 27 ab 28 ab
p value 0.0578 .0069 0.0065 0.0075
Values within each column followed by different letters are significantly different by
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.


Table 2-3. Peel breakdown and decay of 'Valencia' oranges after 44 days of storage
under ambient conditions. The fruit were harvested on 17th June, 2009, 3 weeks after
treatment application.
Total Total
Treatment Sound decay breakdown
Control 50 bc 26 37 a
Foliar K 47 c 31 36 a
Foliar Mg 59 ab 15 31 ab
Foliar K + Mg 54 bc 28 29 ab
1% Vapor Gard 66 a 24 16 b
p value 0.0143 0.2384 0.028
Values within each column followed by different letters are significantly different by
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.


Experiment 2

In the first harvest on 04th December,2009 after 2 weeks of treatment showed no peel

breakdown at all even after 46 days of treatment (Data not shown here). Interestingly,

there was not much decay as well after long durations of storage of this fruit. This trend

was also observed in other fruits harvested at week 3, week 4 and week 6 harvests in









this block (Data not shown here). This could be due to the season of harvest. These

fruits were harvested early in the season. The weather around the month of harvest can

also be a factor in negligible peel breakdown and decay in this experiment.

Experiment 3

In this experiment, the treatments vapor guard 2% and Foliar K + Mg + Vapor

guard 1% showed the highest reductions in peel breakdown compared to untreated

fruit. In the 3rd week after harvest, an interesting trend was observed with most of the

peel breakdown being manifested on the fruit after approximately 25 days of storage

and even when the fruits were stored till 63 days, the total peel breakdown percentage

did not increase more than 2% in all the treatments (table 2-4 and 2-5). The decay

percentage of fruits increased in the meantime. This trend continued in other harvests

as well (data not shown here).

In the table 2-4, peel breakdown and decay of 'Marsh' white grapefruit after 25

days of storage is observed. Foliar K + Mg + 1% Vapor Gard showed no peel

breakdown at all. Vapor Gard 2% showed 8 times less peel breakdown than control

fruit. Hence, Vapor Gard has consistently shown its effectiveness to reduce peel

breakdown and can be recommended to growers for reducing peel breakdown. In the

table 2-5, Peel breakdown and decay of 'Marsh' white grapefruit after 63 days of

storage under ambient conditions is observed. The fruit were harvested 3 weeks after

treatment application. Foliar K + Mg + 1% Vapor Gard and Vapor Gard 2% showed 9

times less peel breakdown than control fruit. Also, even after 63 days of storage, peel

breakdown in fruits irrespective of treatment did not increase by more than 2% as

compared to 25 days of storage. It can be possible that peel breakdown incidence is

manifested till a certain period of time after harvest.










Table 2-4. Peel breakdown and decay of 'Marsh' white grapefruit after 25 days of
storage under ambient conditions. The fruit were harvested on 19th Feb,
2010, 3 weeks after treatment application.
Treatment Sound Total Decay Total


Mg
Vapor Gard1%
K application
Control
Foliar K + Mg
Vapor Gard2%
Foliar K + Mg+ 1%
Vapor Gard


5 bdc
3 dc
1 d
3 bdc
7 bac
7 bac
10 a
10


breakdown
13
9
12
16
8
2
0


Miller cocktail 86 8 ba 5
p value 0.8347 0.015 0.223
Values within each column followed by different letters are significantly different by
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.

Table 2-5. Peel breakdown and decay of 'Marsh' white grapefruit after 63 days of
storage under ambient conditions. The fruit were harvested on 19th Feb,
2010, 3 weeks after treatment application.
Treatment Sound Total Decay Total


Mg
Vapor Gard1%
K application
Control
Foliar K + Mg
Vapor Gard2%
Foliar K + Mg+ 1%
Vapor Gard


breakdown
16
12
13
18
12


Miller cocktail 50 40 13 ba
p value 0.0801 0.1594 0.0056
Values within each column followed by different letters are significantly
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.


different by


Experiment 4

In this experiment, similar trend was followed with most of the peel breakdown being

manifested in the first 30 days of storage in 'Ruby' red grapefruit and not much change









in the percentage of peel breakdown even after prolonged durations of storage (table 2-

6 and 2-7).

The treatment Vapor Gard 2% showed the maximum reduction in peel

breakdown. The average reduction in peel breakdown was 86% followed by foliar K +

Mg + Vapor Gard1%, which had an average reduction 69%. In the table 2-6, peel

breakdown and decay of 'Ruby' red grapefruit after 31 days of storage was observed in

1 week after treatment application with 2% Vapor Gard showing 6 times less reduction

than control fruit. In the table 2-7, peel breakdown and decay of 'Ruby' red grapefruit

after 59 days of storage was observed in 1 week after treatment application with 2%

Vapor Gard showing 5 times less reduction than control fruit. Diplodia was the main

reason for decay in the experiment.

Table 2-6. Peel breakdown and decay of 'Ruby' red grapefruit after 31 days of storage
under ambient conditions. The fruit were harvested on 05th March, 2010, 1
week after treatment application.
Treatment Sound Total Total
Decay breakdown
Mg 62 12 29 ba
Vapor Gard1% 79 21 21 ba
K application 62 21 16 bac
Control 56 16 31 a
Foliar K + Mg 51 27 24 ba
Vapor Gard2% 79 14 5 c
Foliar K + Mg+ 1% 62 27 13 bc
Vapor Gard
Miller cocktail 60 22 22 ba
value 0.1174 0.0906 0.0185
Values within each column followed by different letters are significantly different by
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.









Table 2-7. Peel breakdown and decay of 'Ruby' red grapefruit after 59 days of storage
under ambient conditions. The fruit were harvested on 05th March, 2010, 1
week after treatment application.
Treatment Sound Total Decay Total


Mg
Vapor Gard1%
K application
Control
Foliar K + Mg
Vapor Gard2%
Foliar K + Mg+ 1%
Vapor Gard


ba 46
bac 52
bc 61
bc 48
c 61
a 49
bc 60


Miller cocktail 39 ba 54
p value 0.0189 0.041
Values within each column followed by different
Duncan's multiple range test at P < 0.05.
Significant at P < 0.05.


breakdown
d 29 ba
bdac 21 ba
ba 16 bac
a 31 a
a 24 ba
bdac 6 c
bac 13 bc


bdac 23 ba
0.0271
letters are significantly different by


Experiment 5

In this experiment, there was 96% average reduction in peel breakdown in

'Sugarbelle' mandarin hybrid from the treatment foliar K + Mg but the data was not

significant (data not shown here).









CHAPTER 3
POSTHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF WHITE
GRAPEFRUIT

Introduction

Postharvest factors including humidity, storage time, and storage temperature are

critical to achieve maximum quality of a fresh horticultural commodity. Other

researchers have shown that peel breakdown of fresh citrus may be reduced by

maintaining high relative humidity during storage and shipping (Ben-Yehoshua et al.,

2001; Porat et al., 2004)., Citrus fruit can develop peel pitting even after relatively brief

(3 hours) exposure to low (30%) relative humidity (RH) followed by high (90%) RH after

harvest (Alferez and Burns, 2004).

During the 2006-07 and 2007-08 seasons, peel breakdown was relatively severe

on fresh Florida citrus fruit. The disorder did not appear to be caused by chilling injury

(CI) or postharvest pitting (Petracek et al., 1995), two of the most common causes of

peel breakdown in citrus. In the winter months, especially after cool and/or windy

weather, symptoms of peel pitting and areas of peel necrosis were observed that

progressed into stem-end rind breakdown as the season progressed into spring with

warmer temperatures and when trees were flushing/flowering.

Peel breakdown of 'Fortune' mandarin under cool and low RH conditions was

previously reported (Agusti et al., 1997; Vercher et al 1994), but these reports

suggested the temperature was cold enough to cause CI. As previously stated, CI was

likely not the cause of the Florida peel disorder. Hence, the need to investigate the

possible causes) and best preventative measures) for the Florida disorder. Anecdotal

reports suggested that inclusion of thiabendazole (TBZ) or Imazalil may reduce

postharvest peel breakdown of citrus. While fungicides would not be expected to affect









a physiological disorder, the current experiments included treatments containing TBZ or

Imazalil to evaluate any possible effects. Increased peel breakdown has also been

observed after incomplete rinsing of detergent from the fruit (Petracek et al., 2006).

Thus, the objective of these experiments was to evaluate the effect of exposing fruit to

low (30%) and medium (60%) RH environments and different packingline handling

treatments (i.e., not rinsing detergent from the fruit or inclusion of a fungicide in with the

wax coating) on the development of postharvest peel breakdown of fresh citrus fruit.

Materials and Methods

Fruit

Two separate harvests of 'Marsh' white grapefruit were performed in Vero Beach,

Florida on 26 January and 16 February 2009. Healthy white grapefruit were randomly

harvested from every part of the tree at the height of 1 to 2 meters above ground level.

The trees were healthy and the grove received standard commercial care. These fruits

were transported to Indian River Research and Education Center in Fort Pierce, Florida

on the day of harvest for postharvest treatment.

Humidity Treatments

After harvesting, fruits were kept in plastic crates at different humidity

conditions i.e. 30% RH, 60% RH and 95% RH for 3 days at ambient

temperature of approximately 73 F. Then different packingline treatments were

administered before storing the fruit under ambient conditions of approximately

230C and evaluating weekly for decay and the development of peel and other

physiological disorders. Unless otherwise stated, all fruit were washed with a

detergent, briefly dried, and then coated with carnauba wax (JBT FoodTech,









Lakeland, fla.) before final drying. The standard packingline procedures were

altered depending on the treatment. Treatments are listed below (table 3-1). A

dehumidifier was used to maintain 30% RH, whereas the laboratory

environment maintains approximately 60% RH. Wet rags were placed on fruit

crate tops in the 95% RH environment to maintain high RH levels. Dataloggers

were used to measure air temperatures and RH. A completely randomized

design was used. Each treatment had four replicates of fifty fruits.


Table 3-1. Different humidity and packingline treatment given to 'Marsh' white
grapefruit were performed in Vero Beach, Florida on 26th January and 16
February 2009.
Treatment no. Initial storage RH (%) Changes to packingline
handling
1 30 None
2 60 None
3 90 None
4 95 2000 ppm TBZ
5 95 2000 ppm Imazlil
6 95 Wash but no wax
7 95 No rinse or wax

Decay and Peel Breakdown

Decay and peel breakdown was visually evaluated on each fruit weekly

and the percentage of fruit showing any decay or peel breakdown was

calculated. Decayed fruits were discarded after each evaluation and evaluations

were discontinued after about 50% of the fruits had decayed.

Weight Loss

To measure weight loss, ten fruits were weighed from each replicate at

harvest, after going over packing line, and after 7, 14 and 21 days of storage.

Values are expressed as percent weight lost per day.









Statistical Analysis

Percentage data was transformed to arcsine values and all data were

analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS Institute

Inc, Cary, N.C.). When differences were significant (P < 0.05), individual

treatment means were separated using Duncan's multiple range tests (P =

0.05).



Results and Discussion

Holding fruit for 3 days at different RH significantly affected subsequent

peel breakdown during storage for 25 (Figure 3-1) or 45 (Fig. 3-2) days.

Unwaxed fruits that were kept at 95% RH in prestorage developed

approximately twice the peel breakdown of non-rinsed, unwaxed fruits after 25

days of storage. Fruits, kept at 30% RH in prestorage showed approximately

eight times and five times more peel breakdown than fruits kept at 60% RH in

prestorage after 25 and 45 days of storage respectively (Figure 3.1 and 3.2).

Alferez et al., (2005) reported that Florida citrus can have peel pitting disorder

due to sudden changes in relative humidity after harvest. Fruits kept at 30% RH

received such sudden change in relative humidity. No significant difference was

observed between waxed fruits restored at 60% RH, restored at 95% RH and

restored at 95% RH (with 2000 ppm TBZ + wax) (Figure 3.1 and 3.2). Fruits

treated with wax and 2000 ppm Imazalil, which were kept at 95% RH in

prestorage showed approximately seven times and four times less peel

breakdown than fruits kept at 95% RH in prestorage after 25 and 45 days of









storage respectively (Figure 3-1 and 3-2). Ben-Yehoshua et al. (2001) had

reported that peel breakdown incidence may be reduced by maintaining high

relative humidity during storage but in our study, keeping fruits at high humidity

did not reduce peel breakdown significantly compared to holding at 60% RH.

Interestingly, in this first experiment, inclusion of Imazalil in the wax significantly

reduced postharvest peel breakdown, whereas inclusion of a different fungicide

(TBZ) did not.

For the fruits harvested on 26th January, significant difference in total peel

breakdown was again observed among treatments after 24 and 52 days of

storage (Figure 3-3 and 3-4). Fruits kept at 30% RH during prestorage showed

about four times and three times more peel breakdown than fruits kept at 60%

RH prestorage after 24 and 52 days of storage, respectively (Figure 3-3 and 3-

4). In this experiment, neither fruits treated with 2000 ppm Imazalil nor TBZ

showed any significant reduction in peel breakdown (Figure 3-3 and 3-4).

Hence, Imazlil and TBZ are not effective in reducing peel breakdown

consistently.

The fruit lost water gradually during storage, with fruit pre-stored at 30%

RH loosing significantly more water that fruit pre-stored at 60%, which in tern

lost water significantly faster that fruit stored at 95% RH (Table 3-2). These

differences became insignificant as storage time progressed and the initial water

loss became a smaller fraction of total water loss. The fact that water loss was

slowest after pre-storage at 95% RH concurs with previous research showing

that RH should be maintained as high as possible to keep citrus fruit fresh and









turgid (Ritenour et al., 2003).

There was significant effect of different treatments on decay caused in

fruits harvested on 26th January by diplodia and penicillium (Table 3-3 and 3-4).

Unwaxed fruits, which were kept at 95% RH in prestorage showed

approximately three times and 1.5 times more decay than non-rinsed, unwaxed

fruits kept at 95% RH in prestorage after 24 and 52 days of storage respectively

(Table 3-3 and 3-4). Waxed fruits, which were kept at 30% RH in prestorage

showed approximately three times more decay than fruits kept at 60% RH in

prestorage after 24 and 52 days of storage (Table 3-3 and 3-4). Fruits restored

at 95% RH showed four times less decay than fruits kept at 60% RH in

prestorage after 24 days of storage but no significant difference after 52 days of

storage. Fruits treated with wax and 2000 ppm Imazalil showed three times

more decay than fruits treated with 2000 ppm TBZ after 52 days.

Fungi cause the most serious decay in citrus in Florida and warm, humid

climate of Florida exacerbates the incidence. The most common postharvest

fungus diseases of Florida citrus are Diplodia stem-end rot (Lasiodiplodia

theobromae), green mold (Penicillium digitatum), sour rot (Galactomyces citri-

aurantii) and anthracnose (Colletotrichum gloeosporioides) (Ritenour et al.,

2003). Alternaria stem-end rot (black rot) (Alternaria citri) and brown rot

(Phytophthora palmivora and P. nicotianae) are less frequent in the state of

Florida, but may cause substantial losses in some seasons.

Citrus fruit stored at low relative humidity after harvest are more likely to

decay. Low RH causes stress that promotes peel breakdown and increased









peel breakdown can lead to increased decay (which has been described in

detail in the earlier chapter). Application of a wax coating and fruit storage and

rapid handling at high humidity retards desiccation and maintains fruit turgidity

and freshness compared to washed but not-waxed fruit, but not necessarily un-

washed fruit. Hence, it helps in reducing susceptibility to green mold and stem-

end rind breakdown, thereby, making the fruit less susceptible to decay.

Relative humidity should be 90 to 98% for fruits held in wooden/plastic

containers and 85-90% in fiberboard cartons to prevent the deterioration of

carton (Ritenour et al., 2003).

Thiabendazole (TBZ) is a benzimidazole fungicide and is effective against

Lasiodiplodia theobromae and Penicillium digitatum. It is applied with bin

drenchers and on the packinghouse line. TBZ should be applied at a

concentration of 1,000 ppm (0.1 %) as a water suspension or at 2,000 ppm

(0.2%) in a water-based wax (Ritenour et al., 2003).

Imazalil is very effective against Penicillium digitatum but not much for

control of Lasiodiplodia theobromae and it is ineffective against Phytophthora

palmivora and Galactomyces citri-aurantii. Imazalil should be applied at 1,000

ppm (0.1 %) as a water suspension or at 2,000 ppm (0.2%) in a water base wax

(Ritenour et al., 2003).

Significant effect of different treatments on decay was observed in fruits

harvested on 16th February by diplodia and penicillium (Table 3-5 and 3-6).

Unwaxed fruits, which were kept at 95% RH in prestorage showed

approximately two times less decay than non-rinsed, unwaxed fruits kept at 95%









RH in prestorage after 24 days of storage (Table 3-5). This result is different

from the trend observed in the previous harvest. Waxed fruits, which were kept

at 30% RH in prestorage showed approximately three times and 1.5 times more

decay than fruits kept at 60% RH in prestorage after 24 and 52 days of storage

respectively (Table 3-5 and 3-6). Fruits restored at 95% RH showed 2.5 times

and 1.5 times more decay than fruits kept at 60% RH in prestorage after 24 and

52 days of storage respectively. This result is different from the trend observed

in the previous harvest. Fruits treated with wax and 2000 ppm Imazalil showed

1.5 times less decay than fruits treated with 2000 ppm TBZ after 52 days (Table

3-5 and 3-6).

The results showed TBZ and Imazlil reduced green mould significantly

which concurs with the previous study done by Ritenour et al., (2003).










50.00
45,00

40,00

S35.00
S30,00
S25.00
20,00

15-00
10.00

5.00 C
0.00
Wax Wax Wax Wax + TBZ ax + IMZ No Wax No rinse or
wax

30% RH 60% RH 95% RH 95% RH 95% RH 95% RH 95% RH

Treatments


Figure 3-1. Total peel breakdown (%) of white grapefruit harvested on
16February after 25 days of storage. Bars with different letters are
significantly different by Duncan's multiple range test at P 0.05.










60.00


a
50.00


c 40.00


30,00





10.00 cd cd


0.00
Wax Wax Wax Wax + TBZ Wax + IMZ No Wax No rinse or
wax

30% RH 60% RH 95% RH 95% RH 95% RH 95% RH 95% RH
Treatments


Figure 3-2. Total peel breakdown (%) of white grapefruit harvested on 16
February after 45 days of storage. Bars with different letters are
significantly different by Duncan's multiple range test at P 0.05.











50.00
a
45.00

40.00


30.00

! 25.00

S20,00

15.00


0.00

0.00 -
Wax Wax Wax Wax + TBZ Wax + IMZ No Wax No rinse or
wax

30% RH 60% RH 95% RH 95% RH 95% RH 95% RH 95% RH
Treatments


Figure 3-3. Total peel breakdown (%) of white grapefruit harvested on 26
January after 24 days of storage. Bars with different letters are
significantly different by Duncan's multiple range test at P 0.05.










80.00


70.00 -

S60,00 -

50,00 -
Im
e 40,00 -

30.00 -

20.00 -

10.00 -


-


u.UU -


Wax Wax Wax Wax + TBZ Wax + IMZ No Wax No rinse or
wax
30% RH 60% RH 95% RH 95% RH 95% RH 95% RH 95% RH
Treatments


Figure 3-4. Total peel breakdown (%) of white grapefruit harvested on 26
January after 52 days of storage. Bars with different letters are
significantly different by Duncan's multiple range test at P < 0.05.







Table 3-2. Weight loss in white grapefruit harvested on 26 January after 2, 7, 14 and 21
days of storage at respective relative humidity Different letters are
significantly different by Duncan's multiple range tests at P < 0.05.


Pre 14 Days 21 Days
Storage 2 Days Wt. 7 Days Wt. Wt. Loss Wt. Loss
RH (%) Loss % Loss % % %
30 1.4 a 2.0 a 3.5 a 4.8 a
60 0.9 b 1.9 a 3.4 a 4.7 a
95 0.1 c 1.7a 3.0 b 4.3 b











Table 3-3. Decay (%) of white grapefruit harvested on 26 January after 24 days of
storage Different letters are significantly different by Duncan's multiple range
test at P 5 0.05.


Pre Storage
RH(%)


Packingline
Treatment
Wax
Wax
Wax
2000 ppm TBZ
+ Wax
2000 ppm IMZ
+ Wax
No Wax
No Rinse or
Wax
P-Value


Healthy%
50 b
85 a
93 a


97 a

91 a
86 a


Total decay%
6a
2bc
0 c


0 bc

1 bc
4 ab


94 a
<.0001


1 bc
0.0193


Total
Breakdown (%)
46 a
12b
6 b

1 b

6 b
10b

3b
0.0002


Table 3-4. Decay (%) of white grapefruit harvested on 26 January after 52 days of
storage Different letters are significantly different by Duncan's multiple range test at P <
0.05.


Pre Storage
RH(%)
30
60
95

95

95
95

95


Packingline
Treatment
Wax
Wax
Wax
2000 ppm TBZ
+ Wax
2000 ppm IMZ
+ Wax
No Wax
No Rinse or
Wax
P-Value


Healthy%
27 c
67ab
68ab


87 a

64 b
59 b


Total decay%
24 a
9 bc
12 bc


2 d

7 cd
14b


68 ab
0.0004


9 bc
<.0001


Total
Breakdown (%)
71 a
24 b
14b

10b

28 b
27 b

22 b
0.0002









Table 3-5. Decay (%) of white grapefruit harvested on 16thFebruary after 25 days of
storage Different letters are significantly different by Duncan's multiple range test at P <
0.05.

Pre Storage RH Packingline Total
(%) Treatment Healthy% Total decay% Breakdown (%)
30 Wax 51 c 9 a 43 a
60 Wax 92 a 2 c 5 c
95 Wax 89 ab 6b 3c
2000 ppm TBZ
95 + Wax 92 a 0 c 5 c
2000 ppm IMZ
95 + Wax 99 a 1 c 0 c
95 No Wax 77 b 2c 19 b
No Rinse or
95 Wax 86 ab 5 b 8 bc
P-Value <.0001 <.0001 <.0001


Table 3-6.Decay (%) of white grapefruit harvested on 16thFebruary after 45 days of
storage. Different letters are significantly different by Duncan's multiple range
test at P < 0.05.


Pre Storage RH Packingline
(%) Treatment
30 Wax
60 Wax
95 Wax
2000 ppm TBZ
95 + Wax
2000 ppm IMZ
95 + Wax
95 No Wax
No Rinse or
95 Wax
P-Value


Healthy%
40 d
78 ab
69 bc

76 abc

89 a
62 c

68 bc
<.0001


Total decay%
22a
14bc
21 ab

14 bc

8 c
10 c

13 bc
0.007


Total
Breakdown (%)
49 a
10 cd
10 cd

9 cd

2 d
28 b

19 bc
<.0001










CHAPTER 4
EFFECT OF DIFFERENT COATINGS ON REDUCING FREEZE INJURY OF WHITE
GRAPEFRUIT

Introduction

While Florida is a subtropical environment with an excellent climate for growing

high quality citrus, occasional cold fronts from the north can bring freezing temperatures

in the winter season that may injure fruit and trees. The decade of the 1980s brought a

set of severe freezes to Central Florida, killing many of the state's citrus trees and

shifting the citrus growing region from north and central Florida to south Florida.

Freezing temperatures affected a large portion of Florida's citrus growing areas in

January 1981, January1982, December 1983, January 1985, February 1989 and

December 1989 (Miller, 1991).The citrus producing region of Florida experienced 8

days of sub-freezing temperatures during January 5-13, 2010 (USDA Citrus Forecast

March 2010). Symptoms of freezing injury are internal drying and free juice in the core.

External symptoms of freeze damage on the fruit occur on the outer, sun exposed area

which gets a pink pitting injury. Injury can begin with as little as 2 to 4 hours below -

2.20C. Frost injury in the grove predisposes grapefruit to alternaria stem-end rot on fruit

during storage (Schiffmann-Nadel et al., 1975). Citrus peel is less susceptible to freeze

injury as compared to internal membranes and juice vesicles. Externally uninjured fruit

can contain large areas of completely desiccated tissue, typically at the stem end of the

fruit. As with most other blemishes, the extent of fruit damage permitted varies with local

regulations (Grierson and Ting, 1978). Vapor Gard (Miller Chemical and

Fertilizer, Hanover, Pa.), an antitranspirant, is sold to retard transpiration and maintain

healthy foliage. Antitranspirants are believed to act as barriers to external









nucleators(Levitt, 1980). The antitranspirant film on the surface of the leaves should

impede the frost that forms on the surface from providing a nucleator for water inside

the plant.

Earlier published results of antitranspirants use for reducing freeze injury have

been variable. Dieback of cold-stored sycamore (Platanusoccidentalis L.) seedlings was

reduced after antitranspirant treatment whereas freeze damage to developing peach

(PrunuspersicaBatsch) fruits (Matta et al., 1987; Rieger and Krewer, 1988) and young

citrus trees (Burns, 1970, 1973) was not reduced by antitranspirant treatment.

Carnauba wax (FMC Corporation, Lakeland, fla.) is a coating which is applied to citrus

fruits for reducing weight loss from transpiration losses. We believed that its spray will

impede frost by providing a protective layer over the fruit.

The objective of this study was to evaluate the two commercially available

materials (Vapor Gard and Carnauba wax) for frost and freeze protection of citrus

trees under field conditions and their effect on peel breakdown of grapefruit.

Materials and Methods

Fruit

Experiments were conducted on January 6th, 2010 at two commercial Marsh

White grapefruit groves; one located west of Fort Pierce and the other in Vero Beach,

Florida. Temperature was 200C and wind speed was less than 5 meter per second from

north to south on 6th January, 2010. Spraying operation was performed in the afternoon

on 6th January, 2010.

In the Fort Pierce block, Grapefruit trees were sprayed with either 1% or 5% Vapor

Gard (Miller Chemical and Fertilizer,Hanover, Pa.) or 1:1 or 1:10 dilutions of carnauba

wax(JBT Food techCorporation, Lakeland, fla.). Control trees were left unsprayed. The









experiment was established in a randomized complete block design with each treatment

having three replicates. Single tree replicates were used. Rows were oriented north and

south. In the Vero block, grapefruit trees were sprayed by with either 1% or 5%

carnauba wax or left unsprayed (control). In this block, each treatment had three

replicates.

Harvest and Postharvest Operation:

Fifty fruits were harvested per replicate on January 12, 2010 from both the

experimental sites and brought to Indian River Research and Education Center at Fort

Pierce, Florida on the same day. Fruit were placed in the postharvest lab floor (~23 oC,

50-60% RH) for 3 days before washing and waxing with Carnauba wax. Fruits were cut

in 1/12 in 1/4" slices for freeze injury detection according to the USDA procedure. Two

fruits were cut open per replicate before washing and waxing and noted for any

abnormalities. The remaining fruits from each replicate were washed and waxed and

placed on the postharvest facility floor for evaluation.

A freezing injury scale ranging from 1 (no freezing symptoms) to 9 (severe

freezing symptoms), depending on the severity of freeze injury was used to visually

evaluate the trees for freeze injury (figures 4-3 to 4-9). For example, tree with maximum

leaves having severe freeze injury symptoms were given a rank of 9 in the scale.

Wilting, leaf curl, necrosis and brown spots were used as symptoms of freeze injury in

these evaluations. These four symptoms were combined together to observe the freeze

injury incidence.

Weight Loss

Weight of 10 fruits per replicate was taken after washing and waxing and then

again 15 days later.









Statistical Analysis

Percentage data (peel breakdown, decay) was transformed to arcsine values and

all data was analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS

Institute Inc, Cary, N.C.). When differences were significant (P < 0.05), individual

treatment means were separated using Duncan's multiple range tests (P = 0.05).

Results and Discussion

After the freeze events, trees at the Vero block showed no signs of freeze injury

(data not shown). However, freeze injury symptoms were observed at the Fort Pierce

block where minimum field temperatures dropped lower than in the Vero block (Figure

4-1 and 4-2).

There was no significant difference between treatments with regard to freeze injury.

Fruits were cut immediately after harvest with no visible internal or external injury. No

freeze injury was found in fruit from the Vero block after 24 days storage (data not

shown). Just a few fruit showed freeze damage from the Fort Pierce block after 24 days

storage, but there were no significant difference between treatments (data not shown).

Trees were evaluated for freeze scale and leaf wilting was less and the general

condition of trees looked better than the first evaluation just after freeze (Table 4-1 and

Table 4-2). The trees at Vero block showed no external freeze injury symptoms like

wilted leaves (Data not shown here). External freeze injury symptoms were observed in

Emerald block.









Table 4-1.Fruit drop and tree injury of the Fort Pierce block evaluated on 14January,

2010. Tree injury rating is from 1 (no damage) to 9 (severe damage).


Treatment Fruit Standard Tree Standard
drop error injury error
average average
Carnauba 7.3 2.4 2.3 0.3
1:1
Carnauba 7.0 0.5 4.0 0.0
1:10
Control 4.6 0.8 3.3 1.2
Vapor 4.6 0.3 3.6 0.3
Gard1%
Vapor 3.0 1.1 3.3 0.3
Gard5%


Table 4-2. Fruit drop and tree injury of the Fort Pierce block evaluated on 08February,
2010. Tree injury rating is from 1 (no damage) to 9 (severe damage).


Treatment Fruit Standard Tree Standard
drop error injury error
average average
Carnauba 12.0 2.5 3.3 0.3
1:1
Carnauba 11.3 2.1 4.0 0.0
1:10
Control 4.3 1.4 3.6 0.3
Vapor 10.3 1.8 4.0 0.5
Gard1%
Vapor 5.3 1.8 5.0 0.5
Gard5%











Pro#4


0106M10 129000 AM GMT-0500 01/11410 12I0000 AM GMT-0D00
Figure 4-1.Temperature and RH data from the data logger at Fort Pierce block in the
week of harvest from 01/06/10 to 01/14/10.


Temp. r
4H. 96
~rl
















SPro#



















-60



40





20
50-















O 01~ 01 10 0 12 0L 14 01 1
D0116110 1201 MO AM GMT-ST0S0 D1/1610 12001RI AM GMT.-0500

Figure 4-2. Temperature and RH data from the data logger at Vero block in the week of
harvest from 01/06/10 to 01/14/10.


































Figure 4-3. Freeze injury (Number 9 on the freezing scale).


Figure 4-4. Freeze injury (Number 8 on the freezing scale).


























Figure 4-5. Freeze injury (Number 7 on the freezing scale).


Figure 4-6. Freeze injury (Number 5 on the freezing scale).














Figure 4-7. Freeze injury (Number 4 on the freezing scale).


Figure 4-8. Freeze injury (Number 3 on the freezing scale).


W3T
'. vh';^!^
*l


































Figure 4-9. Least severe freeze injury (Number 2 on the freezing scale).


~ '-' :re '
".' r~. i~-~ ':~t Z;'c- ~









CHAPTER 5
CONCLUSION

The research reported in this thesis has shown the effects of preharvest foliar

potassium (K), magnesium (Mg), or Vapor Gard application, water deficit treatment,

different postharvest humidity conditions and packingline treatments along with storage

time in reducing peel breakdown of citrus. Two commercially available materials (Vapor

Gard and carnauba wax) were evaluated for frost and freeze protection of citrus trees

under field conditions.As a result of these studies, it was found that there was no

significant effect of Vapor Gard or Carnauba wax in reducing freeze injury but there

was very little freeze injury to the fruit.

Foliar applications of K, Mg, K + Mg and 1% Vapor Gard reduced peel

breakdown in 'Valencia' oranges compared to the control fruit in the month of May. 1%

Vapor Gard showed the best results and can be recommended to growers for

reducing peel breakdown in summer. There was increase in total decay with the

increasing days of storage. In the first week of harvest after treatment, the peel

breakdown was very less compared to other harvests.

The white grapefruit harvested in December showed negligible peel breakdown

even after long durations of storage. There was not much decay as well after long

durations of storage of this fruit. This can be possibly due to the effect of seasonal

changes. Early season fruit is less susceptible to peel breakdown as compared to late

season fruit.

The effect of 2% Vapor Gard and the treatment foliar K + Mg + 1% Vapor Gard

in reducing peel breakdown in white grapefruit was very important. In the 3rd week after

harvest, an interesting trend was observed with most of the peel breakdown being









manifested on the fruit after approximately 25 days of storage and even when the fruits

were stored till 63 days, the total peel breakdown percentage did not increase more

than 2% in all the treatments. Hence, there is a possibility that peel breakdown

manifestation is dependent on particular time of storage.

In red grapefruit, similar trend was followed with most of the peel breakdown being

manifested in the first 30 days of storage. The treatment 2% Vapor Gard showed the

maximum reduction in peel breakdown. Hence, the treatment 2% Vapor Gard can be

recommended to reduce peel breakdown in red grapefruit.

Significant differences in postharvest treatments with respect to total peel

breakdown were observed after different durations of storage. After long duration of

storage at ambient conditions, shelf life of fruit held for 2 to 3 days at 30% RH was

reduced by developed about three to eight times more than fruit held at 60% RH.Hence,

fruits kept at 30% RH received sudden change in relative humidity causing more peel

breakdown. Fruits treated with wax and 2000 ppm Imazalil showed inconsistent results

in reducing peel breakdown.

Water loss in the fruit showed gradual losses in every treatment after every

evaluation. The relative differences in weight loss reduced among fruits restored at

30%, 60% and 95% RH for 3 days over longer storage durations. The lowest looses in

water were at 95% RH. The results showed TBZ and Imazalil reduced green mould

significantly. Previous results have also shown their effectiveness in reducing

postharvest decay. Hence, they can be recommended to packers.









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BIOGRAPHICAL SKETCH


Sambhav was born in India. In 2008, he obtained his Bachelor of Science degree

in horticulture from the College of Agriculture, Pune in India. In 2008, he started his

master's program in horticulture at the University of Florida and successfully completed

his degree in 2010.





PAGE 1

1 AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS By SAMBHAV A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2010

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2 2010SAMBHAV

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3 To my family and friends who do not have anything to do with this but I just love them

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4 ACKNOWLEDGMENTS I thank my adviser Dr. Mark Ritenour, who has always been there to listen to me and give his invaluable suggestions in research as well as other aspects of life. He has been a major influence in my life for the last two years, which I feel has made me a better human being. I couldnt have asked for a better adviser. I am greatly indebted to all the awesome people in my lab: Cuifeng Hu, Monty Myers, Jordan Yancy, Kendra Thomason, Kayla Thomason and Andrew Myers for their unw avering support and assistance. I thank the members of my supervisory committee, Dr. Steve Sargent and Dr. Greg McC ollum for all their assistance and insight on this project.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 9 ABSTRACT ................................................................................................................... 10 1 INTRODUCTION .................................................................................................... 12 Taxonomy, Origin and History ................................................................................ 12 Prod uction ............................................................................................................... 12 Quality of Florida Citrus .......................................................................................... 14 Harvest Operations ................................................................................................. 15 Postharvest Operations .......................................................................................... 15 Maintaining Postharvest Quality ............................................................................. 15 Citrus Quality Problems in Florida .......................................................................... 17 Citrus Peel and Peel Breakdown ............................................................................ 17 Pre harvest Peel Disorders .............................................................................. 18 Nutritional or spray damage disorders ....................................................... 18 Weather related disorders .......................................................................... 19 Maturity related disorders .......................................................................... 20 Harves t Related Disorders ............................................................................... 21 Postharvest Related Disorders ......................................................................... 21 2 PREHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF CITRUS ......... 32 Introduction ............................................................................................................. 32 Materials and Methods ............................................................................................ 34 Fruit .................................................................................................................. 34 Experiment 1 .................................................................................................... 36 Experiment 2 .................................................................................................... 36 Experiment 3 .................................................................................................... 36 Experiment 4 .................................................................................................... 37 Experiment 5 .................................................................................................... 37 Fruit Quality Parameters ................................................................................... 37 Peel color ................................................................................................... 37 Peel puncture resistance ........................................................................... 38 Soluble solids content and titratable acidity ............................................... 38 Percent juice .............................................................................................. 38 Statistical analysis ...................................................................................... 38 Results and Discussion ........................................................................................... 39 Experiment 1 .................................................................................................... 39 Experiment 2 .................................................................................................... 40

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6 Experiment 3 .................................................................................................... 41 Experiment 4 .................................................................................................... 42 Experiment 5 .................................................................................................... 44 3 POSTHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF WHITE GRAPEFRUIT ......................................................................................................... 45 Introduction ............................................................................................................. 45 Materials and Methods ............................................................................................ 46 Fruit .................................................................................................................. 46 Humidity Treatments ........................................................................................ 46 Decay and P eel Breakdown ............................................................................ 47 Weight Loss ...................................................................................................... 47 Statistical Analysis ............................................................................................ 48 Results and Discussion ........................................................................................... 48 4 EFFECT OF DIFFERENT COATINGS ON REDUCING FREEZE INJURY OF WHITE GRAPEFRUIT ............................................................................................ 59 Introduction ............................................................................................................. 59 Materials and Methods ............................................................................................ 60 Fruit .................................................................................................................. 60 Harvest and Postharvest Operation: ................................................................ 61 Weight Loss ...................................................................................................... 61 Statistical Analysis ............................................................................................ 62 Results and Discussion ........................................................................................... 62 5 CONCLUSION ........................................................................................................ 70 LIST OF REFERENCES ............................................................................................... 72 BIOGRAPHICAL SKETCH ............................................................................................ 79

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7 LIST OF TABLES Table page 1 1 Optimum holding temperatures for maximum quality and shelf life of fresh Florida citrus fruit ................................................................................................ 16 1 2 Florida Citrus: Production by counties and types, 20082009 ............................ 28 2 1 Grove location, citrus type, rootstock used, soil type and age of grove of the fields where treatments were initiated. ............................................................... 34 2 2 Peel breakdown and decay of Valencia oranges after 44 days of storage under ambient conditions. The fruit were harvested on 10th June, 2009, 2 weeks after treatment application. ...................................................................... 40 2 3 Peel breakdown and decay of Valencia oranges after 44 days of storage under ambient conditions. The fruit were harvested on 17th June, 2009, 3 weeks after treatment application. ...................................................................... 40 2 4 Peel breakdown and decay of Marsh white grapefruit after 25 days of storage under ambient conditions. The fruit were harvested on 19th Feb, 2010, 3 weeks after treatment application. ......................................................... 42 2 5 Peel breakdown and decay of Marsh white grapefruit after 63 days of storage under ambient conditions. The fruit were harvested on 19th Feb, 2010, 3 weeks after treatment application. ......................................................... 42 2 6 Peel breakdown and decay of Ruby red grapefruit after 31 days of storage under ambient conditions. The fruit were harvested on 05th March, 2010, 1 week after treatment application. ........................................................................ 43 2 7 Peel breakdown and decay of Ruby red grapefruit after 59 days of storage under ambient conditions. The fruit were harvested on 05th March, 2010, 1 week after treatment application. ........................................................................ 44 3 1 Different humidity and packingline treatment given to Marsh white grapefruit were performed in Vero Beach, Florida on 26th January and 16 February 2009. .................................................................................................................. 47 3 2 Weight loss in white grapefruit harvested on 26 January after 2, 7, 14 and 21 days of storage at respective relative humidity. .................................................. 56 3 3 Decay (%) of white grapefruit harvested on 26 January after 24 days of storage ............................................................................................................... 57 3 4 Decay (%) of white grapefruit harv ested on 26 January after 52 days of storage. .............................................................................................................. 57

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8 3 5 Decay (%) of white grapefruit harvested on 16thFebruary after 25 days of storage. .............................................................................................................. 58 3 6 Decay (%) of white grapefruit harvested on 16thFebruary after 45 days of storage. .............................................................................................................. 58 4 2 Fruit drop and tree injury of the Fort Pierce block evaluated on 08February, 2010. .. ............................................................................................................... 63

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9 LIST OF FIGURES Figure page 1 1 Major Citrus producing counties in Florida. ......................................................... 28 1 2 Postharvest pitting in grapefruit. ......................................................................... 29 1 3 Stem end rind breakdown in grapefruit. .............................................................. 30 1 4 Wind scarring of grapefruit ................................................................................. 30 1 5 Oleocellosis on grapefruit. .................................................................................. 31 3 1 Total peel breakdown (%) of white grapefruit harvested on 16February after 25 days of storage. ............................................................................................. 53 3 2 Total peel breakdown (%) of white grapefruit harvested on 16 February after 45 days of storage .............................................................................................. 54 3 3 Total peel breakdown (%) of white grapefruit harvested on 26 January after 24 days of storage.. ............................................................................................ 55 3 4 Total peel breakdown (%) of white grapefruit harvested on 26 January after 52 days of storage. ............................................................................................. 56 4 1 Temperature and RH data from the data logger at Fort Pierce block in the week of harvest from 01/06/10 to 01/14/10. ....................................................... 64 4 2 Temperature and RH data from the data logger at Vero block in the week of harvest from 01/06/10 to 01/14/10. ..................................................................... 65 4 3 Freeze injury (Number 9 on the freezing scale). ................................................. 66 4 4 Freeze injury (Number 8 on the freezing scale). ................................................. 66 4 5 Freeze injury (Number 7 on the freezing scale). ................................................. 67 4 6 Freeze injury (Number 5 on the freezing scale). ................................................. 67 4 7 Freeze injury (Number 4 on the freezing scale). ................................................. 68 4 8 Freeze injury (Number 3 on the freezing scale). ................................................. 68

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10 ABSTRACT OF THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE AN INTEGRATED APPROACH TO REDUCE PEEL BREAKDOWN IN CITRUS By SAMBHAV August 2010 Chair: Mark A. Ritenour Major: Horticultural Science Florida is the largest producer of citrus in the U.S.A., especially oranges for the juice market and grapefruit for the fresh market. Peel breakdown of fresh fruit usually manifests itself after packing and shipping and can result in major economic losses. Unusually severe peel breakdown problems were reported during the 200607 and 200708 fresh citrus seasons. Plots were established from 2007 to 2010 in commercial groves using standard fresh fruit growing practices to evaluate the effects of foliar nutritional sprays and water stress on peel breakdown of fresh citrus. Monopotassium phosphate (MKP) was applied at 10.65 Kg M KP per acre (05234; 3.62 Kg K2O per acre) with 1.81 Kg per acre low biuret urea (460 0), magnesium (Mg) was applied at 6% (4.53 Kg E psom salts / 75.70 l iters ), MKP + Mg was applied separately as two tank mixtures, or an antitranspirant (Vapor Gard) was applied at concentrations of 1% and 2% as whole tree foliar sprays at a rate of 473.17 liters per acre. In addition, wholetree water stress was induced by withholding water for up to two months before harvest. Fruit samples were harvested at weekly or biweekly intervals and held at ~ 22.7oC and 5060% RH for three days before washing, coating with carnauba wax and then storing the fruit under ambient conditions. Evaluation of decay and the development of peel disorders and other physiological disorders occurred weekly or biweekly. Tree water

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11 stre ss was measured using a pressure bomb. Incidence of peel breakdown significantly increased after blocking irrigation and rainfall for 49 days before harvest. Foliar applications of K, Mg, K + Mg, or Vapor Gard reduced peel breakdown by about an average of 35.63%, 35.22%, 29.94%, and 45.03% respectively compared to the control fruit during the 200809 season. This trend continued the following season with reductions from Vapor Gard being more pronounced whereas results from foliar K and Mg were not always significant. For postharvest treatments, fruit were held for 3 days at 21oC with 30%, 60%, or 95% RH. Afterwards, fruit were washed, and either left unwaxed, waxed, or coated with wax containing a fungicide (thiabendazole or Imazalil). Significant differ ence in total peel breakdown of different relative humidity treatments was observed among treatments with some consistent trends. Waxed fruits, which were kept at 30% RH in prestorage showed approximately eight times and five times more peel breakdown than fruits kept at 60% RH in prestorage after 25 and 45 days of storage respectively. This trend was observed over repeated experiments Interestingly, in some experiments, adding 2,000 ppm of fungicide Imazalil reduced postharvest peel breakdown.

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12 CHAPTER 1 INTRODUCTION Taxonomy, Origin and History The genus Citrus belongs to the Rutaceae family, subfamily Aurant i oideae. Sweet oranges probably arose in India, the trifoliate orange and mandarin in China and acid citrus types in Malaysia. Citrus was probably introduced in Florida by explorer Ponce de Leons when he brought citrus seeds to Florida in 1493(Michael, 2000). Citrus culture proliferated in Florida in the late 1700's, when the first commercial shipments were made. By the 19992000 season, Floridas citrus industry was one of the largest sources of income and employment in Florida with an overall economic impact of $9 billion, $4 billion in value added, and employed 89,700 people (Hodges et al., 2001). Fresh Florida citrus had an overall economic impact of $1 billion and employed 17,471 in 19992000 season. Thus, research that improves the quality of fresh citrus is economically important to the state of Florida. Floridas citrus industry had an economic impact of $9 billion in industry output, $4 billion in value added, and 89,700 jobs in 19992000 season (Hodges et al., 2001). Fresh Florida citrus account ed for $1 billion in industry output with 17,471 jobs added in 19992000 season. Thus, research that improves the quality of fresh citrus is relevant to the state of Florida. Production Floridas citrus industry is the largest producer of citrus in the United States of America. Seventy one percent of total U.S. citrus production in the 200809 season was from Florida with orange and grapefruit production at 162 million boxes and 21.7 million

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13 boxes respectively. There is a total of 530,900 acres of bearing citrus acres, which is down from the maximum of 941,471 acres in 1970 (Citrus summary, 2002 and 2009). Major citrus growing regions are in South Florida with Polk, Hendry, Highlands and Desoto counties being the top four producers representing 50% of the s tates total citrus production.(Tabl e 12 and Figure 11) (Citrus summary, 2009). The four counties combined accounted for over 55% of the States total orange production. Indian River and St. Lucie counties produced almost 2/3 of the States grapefruit crop (Citrus summary, 2009). Four percent of Florida oranges go to the fresh market while 43% of Florida grapefruit goes to fresh market. The Indian River Research and Education Center in Fort Pierce is located in the heart of this fresh grapefruit growing region and is strategically located in close contact with citrus growers and packers. All citrus are small, spreading, evergreen trees or tall shrubs. Plantings are usually in rectangular arrangements which eventually become tall hedgerows. Spacings are typically 20 x 25m for grapefruit and vigorous trees, 15 x 20m for oranges and tangerines, and 1215m x 1820m for limes and smaller cultivars. Tree densities are about 100110 trees/acre for grapefruit, and 130140 for sweet orange. Very litt le training is needed for citrus but the trees are pruned at regular intervals. Citrus trees are generally budded onto various rootstocks, which are chosen based on rootstocks hor ticultural traits like yield, resistanc e to pests and diseases or tolerance to soil type. Drip irrigation is primarily used to supply water and fer tilizer (Tucker, 1978). Over 97% of Florida citrus is irrigated. Micro irrigat ion methods are used on over 67% of irrigated citrus groves (Marella, 1995).

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14 Quality of Florida Citrus Florida citrus is known all over the world for its quality. Florida citrus has different quality factors for the fresh and processing markets. For juice, the most important quality factors include fruit juice content, fruit size, color, soluble solids and acid concentrations and soluble solids acid ratio. In addition to internal quality, fruit size, shape, color and maturity date are important for fresh fruit. Ruby Red, Flame and Marsh are important grapefr uit varieties, Hamlin and Navel are important orange varieties, and Sunburst, Honey and Fallglo are important varieties of mandarin. Grapefruit, navel oranges, tangerines, and mandarin hybrids fetch relatively high economic returns as fresh fruit but low returns when they are diverted for the juice market because of poor external quality (i.e., peel blemishes) ( Stelinski et al., 2009). Florida citrus is known all over the world for its quality. It is used both for fresh market as well as for ext racting juice. Juice is particularly of high quality. The most important quality factors include fruit juice content, fruit size, color, soluble solids and acid concentrations and soluble solids acid ratio. Florida citrus growers have different quality fac tors for the fresh and processing markets. Fruit size, shape, color and maturity date are most important for fresh fruit but high juice content and soluble solids are important for fruits used in processing. Ruby Red, Flame and Marsh are important varieties of grapefruit. Hamlin and Navel are important varieties of orange. Sunburst, Honey and Fallglo are important varieties of mandarin. Grapefruit, navel oranges, tangerines, and mandarin hybrids fetch higher value in fresh market and relativ ely lower value in processing market ( Stelinski et al., 2009).

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15 Harvest Operations All citrus are nonclimacteric fruit; they mature gradually over weeks or months and are slow to abscise from the tree. Hence, they store best on the tree for most of the season. External color changes during maturation, but it is a poor indicator of maturity. The best indices of citrus maturity are internal: total soluble solids, acid content, and the total soluble solids/acid ratio (Kader, 1999). For example, a high quality fresh market grapefruit will be elliptical and firm relatively blemishf ree with a turgid, smooth peel ( Soule and Grierson, 1986). The fruit will have an appropriate balance of soluble solids: titratable acidity with minimum bitterness. The harvesting season for Florida citrus is usually from September June. Grapefruit availability is throughout the season whereas different varieties of orange span the season. Specialty fruits like temples, k early Citrus, tangelos and tangerines are available for shorter periods during the season. Citrus is harvested both mechanically and manually in Florida. However, all fresh citrus is harvested by hand using ladders, bags, bins, conventional fruit loading trucks or goats and flat bed trucks. Postharvest Operations Citrus fruits are transported to packinghouse s, where they are handled differently depending on their intended use. S tandard packing line operations include dumping onto the packing line, culling, presizing, washing, drying, grading, waxing, drying, final grade, sizing, and packing into approved containers. Maintaining Postharvest Quality Cultivar, environmental conditions, and postharvest handling practices are important factors in determining postharvest quality. Cultivar selection is important in addr essing postharvest quality issues such as firmness, because most of these are

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16 genetically controlled (Prange and DeEll, 1997). Environmental conditions can influence postharvest quality in citrus and other commodities (Kader, 2002; Prange and DeEll, 1997). Fruit size is an important factor of quality for fresh citrus consumption (Agusti, 1999). Optimum storage temperature of citrus ranges from 0 to 15oC depending on citrus variety and time of year (Table 11). Kumquats and mandarins are the most cold tolerant whereas Limes and citrons are the least (Ladaniya, 2008). Early season, unwaxed grapefruit should be shipped at 15C to avoid chilling injury (Ritenour et al., 2003). Later in the season, temperature can be reduced to 12C and then to 10C. Late season grapefruit should be handled at 15 C as it may become susceptible to chilling injury and decay. Depending on the gas diffusion of a particular wax formulation, waxed citrus can be held at lower temperatures without developing chilling injury compared to nonwaxed fruit. Postharvest handling also influences the quality of a commodity. For optimum quality and quality retention during postharvest handling, fresh citrus must also be harvested at the correct maturity stage. For example, postharvest physiologic al disorders are more likely in fruits picked too early or too late in their season than in fruits picked at their optimum maturity (Kader, 1999). Table 11. Optimum holding temperatures for maximum quality and shelf life of fresh Florida citrus fruit Cit rus type Optimum holding temperature ( 0 C) Oranges 0 1 Mandarin type fruits 4 Lemon, Limes 10 Grapefruit 10 15

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17 Citrus Quality Problems in Florida Citrus quality in Florida can be negatively affected by many disorders, making it unacceptable for the fresh market. When the fruit is not suitable for the fresh market, it is consigned for juice purposes, which leads to less profit to the grower. It is a much worse situation if the disorder develops during shipment, which results in rejection at the destination. This leads to higher losses as the cost of shipping is also incurred. In addition, when the buyer receives such fruit, they are less inclined to purchase fruit from that shipper again. Among the diseases and disorders that render citrus fruit unsuitable for the fresh market are 1) physical injuries such as cuts and punctures, 2) infestation with pests such as the Caribbean fruit fly, 3) pathological disorders resulting in decay or peel blemishes (i.e., from melanose, canker, etc.), and 4) physiological disorders such as stem end rind breakdown or chilling injury. Citrus Peel and Peel Breakdown The citrus rind consists of the flavedo and albedo. The flavedo comprises the outermost part of the rind and includes the cuticle, epid ermal cells, sub epidermal cells and oil glands (Schneider, 1968). The albedo comprises the internal spongy white part of the peel and primarily contains parenchyma cells interspread with vascular bundles. Peel disorders severely degrades the fruit appearance, but usually do not affect the edible or nutritive quality of the fruit (Petracek et al., 2006). In addition, peel disorders predispose the fruit to invasion by decay organisms, thus reducing postharvest shelf life (Hopkins and McCornack, 1960; McCornack, 1973; Smoot, 1977; SchiffmannNadel et al., 1975). Peel disorders are difficult to study for several reasons: they can appear and disappear unpredictably and a single disorder can have multiple symptoms while multiple disorders may have similar symptom s, even in the same fruit. Unlike diseases,

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18 which can be positively identified by isolating the causal pathogenic organisms, there are typically no single factors that critically define a disorder (Petracek et al., 2006). Hence, it is often difficult to di agnose physiological disorders. Most peel disorders such as chilling injury, postharvest pitting, oleocellosis, and zebra skin start in the flavedo but some such as creasing originate in the albedo. Peel disorders can be classified as preharvest, harvest or postharvest disorders based on their time of appearance. Pre harvest Peel Disorders Preharvest peel disorders can be classified as nutritional, spray damage, weather, or maturity related depending on the cause of the disorder. Nutritional or spray damage disorders Aging and stem end rind breakdown: Detailed information on thi s disorder is given in the postharvest section of this chapter Boron deficiency: As the name suggests, this disorder is caused by boron deficiency. Symptoms include raised bumps on the fruit surface and gummy pockets in the albedo that are visible when the fruit is cut open (Bryan 1950; Browning et al., 1995). Pineapple pitting: Pineapple oranges are more susceptible to this disorder than other citrus varieties. Low potassium levels in adjacent leaves is the main cause (Grierson, 1965).Symptoms include the collapse of small areas of the flavedo around the shoulder and cheek of the orange peel. Darkening and coalesce of pitted areas may be seen (Browning et al., 1995; Smoot et al., 1971).

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19 Spray damage: The main causes of this disorder are incompatible tank mix chemical combinations, incorrect application rates or timings or a phytot oxic active ingredient in the mixture (Al brigo and Grosser, 1996). Main s ymptoms are streaks of damaged or non degreened cells running longitudinally down the fruit surface or by rings at fruit to fruit or leaf to fruit contact points. Ammoniation: Ammoniation is observed when nitrogen is used in excess on copper deficient soil (Browning et al., 1995; Smoot et al., 1971). Main symptoms are black or brown raised lesions on fruit. Weather related disorders Aging and stem end rind breakdown: Detailed information on this disorder is given in the postharvest section of this chapter. Freeze injury: Exposure to low enough temperatures in the field that results in ice formation within the fruit is the cause for this injury. Symptoms of freezing injury are internal drying and free juice in the core of fruit. Externally, a pinkish pitting may develop. Even lighter frost i njury in the grove may predispose grapefruit to alternaria stem end rot during storage (SchiffmannNadel et al., 1975). Sunburn: Temperature of 44.4o C and 20% relative humidity has been shown to cause sunburn to Valencia (Ketchie and Ballard, 1968). The typi cal symptoms are flat, pale, leathery areas on the exposed side of fruit (Smoot et al., 1971). Water spot: Water soaking and swelling of the rind around the stylar end is observed in this disorder. It is a typical prob lem of Navel oranges produced under

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20 low humidity conditions that are then subjected to a cool, wet period (Scott and baker, 1947; Klotz, 1975; Riehl and Carman, 1953; Smoot et al., 1971). Wind scar ring : It is a problem in areas where high wind velocity coi ncides with post bloom period. Small (less than 1 cm in diameter) citrus fruits are so susceptible to abrasion injury that just rubbing against a leaf can cause lesions that expand to large silvery or tan blemishes as the fruit enlarges (Figure 14) (Elmer et al., 1973; Freeman, 1976; Smoot et al., 1971). Maturity related disorders Creasing: The exact cause is unknown. Potassium nutrition, rootstock and water relations are considered to be probable factors (Bar Akiva, 1975; Embleton et al., 1971; Grierson, 1965). Main symptoms are grooves or furrows which are irregularly distributed on the fruit surface (Browning et al., 1995; Smoot et al., 1971). Puffiness: It is the separation of peel from the pulp. Advancing fruit maturity, tree vigor and weather (particularly irregular water supply) are the main factors involved in this disorder (Grossenbacher, 1941; Kuraoka, 1962). Rind staining of navel oranges: It occurs when the peel is so physiologically over mature that epidermal wax softens and handling causes reddish brown blemishes (Eaks, 1964). Brownish discoloration of the rind surface is the characteristic symptom. The susceptibility is increased by ethylene exposure, use of certain rootstocks such as Rubidox sour and rough lemon, and in trees having high nitrogen fertilization (Eaks, 1969).

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21 Harvest Related Disorders Blossom end c learing of grapefruit: Rough handling of late season fruit during warm temperatures is the primary cause of this disorder. It is characterized by the translucent, water soaked appearanc e of the fruit peel (most commonly at the blossom end) caused by internal bruising and juice leakage from juice vesicles (McCornack, 1966). Oleocellosis: It is breaking of oil cells, causing the oil to extrude which damages the surrounding tissues. Symptom s include discrete spots on the peel, large scalded areas, and concentric rings of small lesions (Figure 15) (Turrell et al., 1964). The main cause of this disorder is rough handling of very turgid fruit (Eaks, 1969; Smoot et al., 1971; Nel et al., 1974; Wardowski et al., 1976). Red colored lesions: These develop when superficial wounds, no deeper than the flavedo, develop a reddish color in the lesions and surrounding peel. It is attributed to a reaction in peel tissue that forms compounds that impart res istance to infection by Pennicillium digitatum (Kavanagh and Wood, 1967). Postharvest Related D isorders Aging and stem end rind breakdown (SERB) : Symptoms involve the collapse and subsequent darkening of epidermal tissues, particularly around the stem end of citrus fruit. A narrow 2 to 5 mm ring of undamaged tissue immediately around the calyx is a characteristic symptom of SERB (Figure 13). Aging of oranges and grapefruit which can occur after long term storage is almost indistinguishable from SERB, except that the characteristic narrow ring of healthy cells does not

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22 tend to persist around the calyx (Smoot et al., 1971).SERB is most severe on oranges and Temples, but it may also occur on tangelos and grapefruit. Small and well colored fruit are most susceptible to this disorder. The humid environment of Florida makes the thinner skinned fruit more prone to SERB than thicker skinned fruit from drier, Mediterranean environments. Fruits affected with this disorder are more prone to decay during postharvest handling and marketing. The exact cause of SERB is uncertain. It is primarily associated with drying conditions. These drying conditions are due to f actors such as delays in packing, holding fruit under low humidity and high temperatures, and excessive air movement around the fruit (McCornack and Grierson, 1965). Nutritional imbalances involving nitrogen and potassium can also be a cause (Chapman, 1958). Chilling injury (CI) : It is a common disorder characterized by the collapse of discrete areas of peel that form sunken lesions which tend to coalesce. It is induced by low temperature i.e. below 10o C storage (Chace et al., 1966). At very low temperatures, superficial scalding may occur instead of pitting. It is typically reddish or tan colored. Browning of the albedo and of carpellary membranes is peculiar to lemons. In grapefruit and tangelos, oil glands may darken (Smoot et al., 1971). In Florida, gr apefruit are most susceptible to CI early (October December) and late (MarchMay) in the season. The fruit usually become more resistant to CI during midseason (December March). Postharvest temperature treatments have been used to prevent CI. Intermittent warming throughout the storage period, stepwise lowering of temperature, and prestorage heat

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23 treatments can mitigate CI (Davis and Hoffman, 1973). Delayed storage and storage at high relative humidity can lower the incidence of CI (Pantastacio et al., 1966). Very high initial concentrations of CO2 can mitigate CI (Brooks et al., 1936; Vakis et al., 1970; Hatton et al.,1975). Methyl jasmonate (Meir et al., 1996) and squalene treatment (Nordby and McDonald, 1990) have shown some protection from CI. Drench phytotoxicity: Long term, unmonitored use of drench solution can lead to the accumulation of chemicals including salts, preharvest agro chemicals washed from the fruit, and even motor oil from truck drenches. If these chemicals reach phytotoxic concentrati ons, peel damage will occur. Symptoms include discolored circular and streaking patterns. The disorder may be called Green Ring due to characteristic green circles at fruit contact points with other fruit and bin surfaces that are evident after degreening (Ritenour and Dou, 2000). Postharvest pitting: It is characterized by clusters of collapsed oil glands scattered over the fruit surface (Figure 12) (Petracek and Davis, 2000). Application of waxes with low gas transmission rates exacerbates the disorder ( Petracek et al., 1998). Symptoms of postharvest pitting may also arise after exposure to low (i.e., 30%) relative humidity environments after harvest, but it is unclear these disorders share a common fundamental mechanism (Alferez and Zacarias, 2001). Rind staining of navelina oranges: It is characterized by collapse and drying of flavedo and eventually by darkening of affected area over time (Laufente and

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24 Sala, 2002). It is observed mainly in navel oranges. It is both a preand postharvest disorder. Rind staining occurs at the stage when the peel is physiologically over mature and epidermal wax softens. Hence, handling causes reddishbrown blemishes (Eaks, 1964). Ethylene treatment, high rates of nitrogen fertilization and root stocks that promote vigorous growth make fruit susceptible to this disorder. Peel breakdown problems were severe during the 2006 07 and 2007 08 seasons in Florida. According to industry estimates, these two seasons has cost the fresh citrus industry as much as $1 million in claims both years. These breakdown problems were not associated with chilling injury (Petracek et al., 1995). The common disorders observed in this study were general peel breakdown and SERB. Symptoms included areas of peel pitting and necrosis that appeared dur ing the winter months, especially after cool and/or windy weather, and progressed into the spring as stem end rind breakdown (Ritenour and Dou, 2003) when trees were flushing/flowering and temperatures were warming. The occurrence of peel breakdown of For tune mandarin under cool and low relative humidity (RH) conditions was also reported (Agusti et al., 1997; Vercher et al., 1994), but these reports suggested the temperature was cold enough to cause CI. As previously stated, CI was not likely the cause of the Florida peel disorder. Recent studies in Florida have shown that sudden changes in relative humidity (RH; e.g., from 30% to 90%) after harvest can cause peel pitting of Florida citrus that is not related to CI (Alferez and Burns, 2004; Alferez et al., 2005).Of the preharvest factors, plant nutrition imbalance concerning

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25 potassium and nitrogen and water stress have been suggested as potential factors influencing the susceptibility of citrus fruit to postharvest peel breakdown (Alferez et al., 2005; Grie rson, 1965). For example, SERB has been reported by some to be more severe when fruit are harvested from water stressed trees compared to nonstressed trees, whereas others have found no significant relationship (Grierson, 1965). In addition, researchers i n other countries found that nutritional imbalances involving high N and low K may predispose fruit to SERB (Chapman, 1958; Grierson, 1965). No conclusive relationship between plant water stress, low K, high N, and SERB development under Florida conditions has been demonstrated. R ecent research showed reduced peel breakdown after a preharvest magnesium (Mg) application on Nules Clementine mandarin in South Africa (Cronje et al., 2008). Improved plant water status was observed from the emulsions of wax, latex and plastic that dries on the foliage and forms thin films (Gu et al., 1996; Hummel, 1990; Nitzsche et al., 1991; Plaut et al., 2004). Foliar application of this emulsion minimized plant water loss by decreasing stomatal conductance (gs), and reducing transpirational losses,. Better appearance and excellent weathering resistance was observed after the application of polyterpene antitranspirant, pinolene on the orange surface (Albrigo, 1970). SERB, oleocelosis and creasing can be reduced by using preharvest antitranspirants spray (Albrigo, 1970). The current studies were initiated to evaluate various preand postharvest treatments to better understand the factors related to the development and prevention of postharvest peel breakdown on fresh citrus. Based on the above

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26 information related to the disorder, experiments were designed to test the hypothesis that postharvest peel breakdown can be reduced by improving plant nutrition through foliar K, Mg, or K + Mg sprays before harvest, reducing preharvest water stress of the trees, or by preventing postharvest exposure to low RH conditions. The objectives of this study were to evaluate the potential effect of preharvest plant water stress and foliar K, Mg and antitranspirant applications on postharvest peel breakdown of fresh Florida citrus (especially grapefruit). In addition, the effects of holding fruit under different RH conditions after harvest and the effects of different packingline treatments on peel breakdown were also evaluated. The goal was to bet ter predict what conditions promote and retard peel breakdown, and to develop production and postharvest practices to reduce or eliminate the occurrence of this disorder.

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27 Table 12. Florida Citrus: Production by counties and types, 20082009 County All Oranges Grapefruit Citrus Early -mid Late All White Colored All Navel Temple (Valencia) 1,000 boxes Brevard 806 381 303 684 25 56 81 Charlotte 3,503 907 1,973 2,880 12 409 421 Collier 10,069 4,290 5,214 9,504 29 383 412 DeSoto 20,639 9,068 11,198 20,266 26 193 219 Glades 3,057 1,598 1,330 2,928 9 34 43 Hardee 15,366 10,463 4,341 14,804 68 197 265 Hendry 21,796 8,274 12,201 20,475 250 723 973 Hernando 294 270 6 276 6 6 Highlands 23,219 9,670 12,417 22,087 382 358 740 Hillsborough 4,110 2,964 899 3,863 18 33 51 Indian River 11,434 2,320 1,684 4,004 2,751 4,519 7,270 Lake 4,737 2,636 947 3,583 59 476 535 Lee 3,226 1,070 1,786 2,856 19 264 283 Manatee 7,293 4,301 2,724 7,025 64 124 188 Marion 381 266 60 326 3 14 17 Martin 5,309 1,653 3,419 5,072 70 116 186 Okeechobee 2,137 950 787 1,737 110 220 330 Orange 1,359 783 465 1,248 8 36 44 Osceola 3,581 2,113 940 3,053 257 191 448 Palm Beach 237 12 12 50 50 Pasco 2,945 2,249 577 2,826 9 37 46 Polk 30,253 16,007 11,145 27,152 705 1,057 1,762 St. Lucie 12,329 1,873 3,175 5,048 1,686 5,386 7,072 Sarasota 439 96 138 234 22 152 174 Seminole 156 100 21 121 13 13 Volusia 292 192 40 232 16 36 52 Total 189,100 84,600 77,800 162,400 6,600 15,100 21,700

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28 Figure 11.Major Citrus producing counties in Florida. Adapted from USDA, NASS Citrus summary 200809.County no. 46Polk, County no. 54Highlands, County no. 53Desoto, County no. 62Hendry and County no. 56Indian River County.

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29 Figure 12. Postharvest pitting in grapefruit.

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30 Figure 13 Stem end rind breakdown in grapefruit. Figure 14. Wind sc arring of grapefruit

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31 Figure 15. Oleocellosis o n grapefruit.

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32 CHAPTER 2 PREHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF CITRUS Introduction Plant nutrition and water stress have been suggested as potential preharvest factors influencing the susceptibility of citrus fruit to postharvest peel breakdown (Alferez et al., 2005; Grierson, 1965). However, results have not been conclusive. For example, some authors have reported SERB to be more severe when fruit are harvested from water stressed trees compared to nonstressed trees, whereas others have found no significant relationship with water stress (Grierson, 1965). It has also been found that nutritional imbalances involving high nitrogen (N) and low potassium (K) may predispose fruit to SERB (Chapman, 1958; Grierson, 1965). While no conclusive relationship between plant water stress, low K, high N, and SERB development under Florida conditions has been demonstrated, trends in data taken in 200708 season supported further study and the potential use of alternate application methods. Potassium nutrition is emerging as potentially a key factor in influencing peel health of citrus especially its interact ion with different nutrients or climatic factors (Bar Akiva, 1975; Embleton et al., 1971; Grierson, 1965). Fruit rind K deficiency was observed as superficial rind pitting (SRP) in Shamouti oranges (Tamim et al ., 2000), while Kdeficiency increased creas ing in many mandarin varieties and Valencia orange (Raber et al ., 1997). Foliar applied potassium has also been found to increase citrus fruit size, specific fruit components and increased yields in recent studies (Achilea 2000; Erner et al., 1993). Low plant K levels have also been associated with other citrus peel disorders such as creasing and Pineapple orange peel pitting (Petracek et al., 1995). Increased K

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33 fertilization has been reported to increase fruit size, weight, vitamin C content, and f ruit storage potential (Embelton et al., 1975). Though high levels of K fertilization may have some negative effects, such as decrease sugar to acid ratio and color development, foliar K applications have been reported to increase size without decreasing s ugar to acid ratios, total soluble solids (TSS), acid or juice contents and with no increase in peel thickness (Boman, 1997; Boman and Hebb, 1998). Imbalances between N and K have also been reported to affect peel breakdown in citrus (Petracek et al., 1995).Magnesium (Mg) nutrition was recently reported to reduce peel breakdown of Nules Clementine mandarin in South Africa ( Cronje et al., 2008). Vapor Gard forms a film on plant tissues and reduces transpiration by 25% to 80% depending on the plant tissue (Davenport et al., 1976, EI Sharkawy et al., 1976). Studies showed that antitranspirant application can increase leaf water potential in bell pepper (Berkowitz and Rabin, 1988; Nitzsche et al., 1991). The emulsions of wax, latex and plastic that dried on the foliage and formed thin films improved plant water status. It minimizes transpiration and plant water loss by decreasing stomatal conductance (gs) (Gu et al., 1996; Hummel, 1990; Nitzsche et al., 1991; Plaut et al., 2004). Better appearance of fruit and excellent weathering resistance was observed after the application of a polyterpene antitranspirant, Pinolene on the orange surface topography (Albrigo et al., 1970). SERB and creasing can be reduced by using preharvest antitranspirant spray and was, therefore, included in this study. The objective of the current research was to evaluate the potential effect of plant water stress and preharvest foliar K, Mg and antitranspirant application on postharvest peel breakdown of fresh Florida citrus (especially grapefruit).

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34 Materials and Methods Fruit Valencia oranges, Marsh white grapefruit, Sugar Belle mandarin hybrid and Ruby red grapefruit were used for the different experiments. Trees were located in commercial citrus blocks and received standard cultural practices used for fresh fruit. The grove location, citrus type, rootstock used, soil type and age of grove of the fields where treatment was initiated is followed below (Table 21). Table 21. Grove location, citrus type, rootstock used, soil type and age of grove of the fields where treatments were initiated. Grove location Citrus type Rootstock used Predominant soil type Age of grove Vero Beach Valencia orange Sour orange Winder fine sand 25 Fort Pierce Marsh white grapefruit Sour orange Pineda fine sand 21 Fort Pierce Marsh white grapefruit Cleoparta Wabasso fine sand 21 Vero Beach Ruby red grapefruit Sour orange Riviera fine sand 30 Vero Beach Sugar Belle mandarin hybrid Unknown Riviera fine sand Unknown For each experiment, whole trees were exposed to different combinations of the following treatments: Control ( unsprayed trees with normal irrigation) Foliar applied K (10.6 Kg MKP/acre [05234]; 3.6 Kg K2O/acre) with 1.8 Kg per acre low biuret urea (460 0) Foliar applied Mg (6% [4.53 Kg Epsom salts /75.7 l iters])

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35 Foliar applied K plus Mg. Applied separately as two tank mixtures with the same concentrations used above. Foliar applied Vapor Gard (1% = 473.1 liters per acre). Irrigation deficit (1 month before harvest plugged irrigation jets and Tveyk was laid around the base of the trees to prevent rain from replenishing soil moisture). Vapor Gard (2%). Unless otherwise stated, field plots were established in a randomized complete block design with 4 replicates of 5 trees each. Foliar treatments were spr ayed to all sides of the tree uniformly at a rate of approximately 473.1 liters/acre. Fruits were evaluated from middle 3 trees. Fruit were harvested 7, 14, 21, 28 and/or 35 days after spraying. Fifty fruits were harvested per replicate and brought to Indian River Research and Education Center at Fort Pierce, Florida on the same day. Fruit were placed on the postharvest lab floor (~23 0C, 50 60% RH) for 3 or 4 days before washing and waxing. Ten extra fruits were harvested for internal quality assessment in the 3rd week after spraying. Fruits were washed and rinsed (without SOPP, chlorine or any other fungicides) and waxed (carnauba, FMC Corporation). Fruits were then kept under ambient conditions on the postharvest facility floor (~ 23 0C), conditions thought to promote peel breakdown. Decay and peel breakdown was visually evaluated on each fruit and the percentage of fruit showing any decay or peel breakdown was calculated. Decayed fruits were discarded from the replicate after each week of evaluation.

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36 Experiment 1 Treatments were initiated on 27 May, 2009 in a Vero Beach block of Valencia oranges. Spraying started at 12 pm and was completed at 2 pm. Wind velocity was less than 2 meter per second and the air temperature was 34o C. Field treatments inc luded foliar applications of K, Mg, K plus Mg and 1% Vapor Gard. Experiment 2 Treatments were initiated on 20 November, 2009 with Marsh white grapefruit in Fort Pierce, Florida. Spraying started at 10 a.m. Air temperature was 21oC and wind velocity was less than 2 meter per second. Irrigation jets were plugged to stop irrigation in the respective treatment on the same day. Field treatments included foliar applications of K, Mg, 1% & 2% Vapor Gard and withholding irrigation rain. Fruit were harvested 14, 21 and 35 days after treatment. Fruit from the irrigation deficit treatment were harvested 35 days after treatment initiation. Forty fruits were harvested per replicate from the experimental site. Experiment 3 Treatments were ini tiated on 26 January, 2010 with Marsh white grapefruit in Fort Pierce, Florida. Spraying was done in the afternoon. Wind velocity was 4 meter per second. Temperature was 20o C. Field treatments included foliar applications of K, Mg, 1% & 2% Vapor Gard, Foliar K, Mg, & 1 % Vapor guard (applied separately, in that order), Miller cocktail (Calexin; Millerplex; Greenstim; 1% Vapor Guard) and withholding irrigation/rain. Field Treatments were done in RCB design with 4 replicates of 3 trees each. Fruits were evaluated from middle tree. Fruit were harvested after 1, 3, 5 and 7 weeks after treatment. Irrigation deficit treatment fruit were harvested 5 weeks after treatment. Forty Fruits were harvested per replicate.

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37 Experiment 4 Treatments were initiated on 23 February, 2010 with Ruby red grapefruit in Vero Beach, Florida. Spraying was done in the afternoon. Wind velocity was approximately 2 miles per hr. Temperature was 25o C. Field treatments included foliar applications of K, Mg, 1% & 2% Vapor Gard, Foliar K, Mg, & 1 % Vapor guard (applied separately, in that order) and Miller cocktail (Calexin; Millerplex; Greenstim; 1% Vapor Guard).Field t reatments were done in RCB design with 4 replicates of 3 trees each. Fruits were evaluated from middle tree. Fruit were harvested after 1 and 3 weeks after treatment. Forty fruits were harvested per replicate. Experiment 5 Treatments were initiated on 14 December, 2009 with Sugar Bells, a mandarin hybrid in Vero Beach, Florida. Spraying was done in the afternoon at 3 p.m. Temperature was 25oC and wind speed was 2 meter per second from east to west. Single tree replicates were used. Field treatments included foliar applications of K and Mg. Four reps of 1 tree each were used for treatments. Fruit were harvested after 1, 7 and 21 days after treatment. Sixty Fruits were harvested per replicate. Fruit Quality P arameters Peel color Peel color was measured using a Minolta Chroma Meter (CR 300 series, Minolta Co. Ltd., Japan) at three equidistant locat ions on each fruit along the equator of the fruit and expressed as L*, a* and b* values. The hue and chroma values were calculated from a* and b* values using the following formulas: Hue = arc tangent (b*a*1) Chroma = (a*2 + b*2)1/2

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38 Peel puncture resi stance Peel puncture resistance was measured at two equidistant spots along the equator of each fruit using a texture analyzer (Model TAXT2i, Stable Micro Systems, Godalming, England) with a 2 mm diameter, flat tipped, cylindrical probe. The analyzer was s et so the probe traveled at a speed of 2 mms1 and the maximum force exerted to puncture the peel recorded. Peel puncture resistance was expressed in Newtons. Soluble solids content and titratable acidity Fruit were cut into halves along the equator and j uice was extracted using a test juice extractor (Model 2700, Brown Citrus Systems Inc., Winter Haven, Fla.). Juice total soluble solids (TSS) was measured using a temperaturecompensated refractometer (Abbe3L, Spectronic Instruments Inc., Rochester, N.Y.) and the juice titrable acidity (% citric acid) was measured by titrating 40 mL of juice samples to pH 8.3 with 0.3125 N NaOH using an automatic titrimeter (DL 12, Mettler Toledo Inc., Columbus, Ohio). Percent juice Percent juice was calculated from the t otal weight of fruit and total weight of juice. Percent juice = Juice weight (g) 100/ Fruit weight (g) Statistical analysis Percentage data (peel breakdown, decay) was transformed to arcsine values and all data were analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS Institute Inc, Cary, N.C.). When differences were significant (P < 0.05), individual treatment means were separated using Duncans multiple range tests (P = 0.05).

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39 Results and Discussion Experiment 1 There was no significant difference among the treatments for peel color, total soluble solids and titratable acidity, peel puncture resistance and juice percent (data not shown here). Foliar applications of K, Mg, K + Mg, and Vapor Gard reduced peel breakdown by about an average of 35%, 35%, 29%, and 45% respectively compared to the control fruit. Peel breakdown and fruit decay increased as storage durati on increased. Peel breakdown was much lower in fruit harvested 1 week after field treatments were administered compared t o the other harvests (Table 2 2 and 23 ).This trend was also observed in other experiments (data not shown here) This coincides with t he previous study done (Ritenour et al., 2008). In the table 22, decay and peel breakdown of Valencia orange is shown. Total peel breakdown is the aggregate of all types of peel breakdown observed in the fruit. In this experiment, the total peel breakdown was due to general breakdown and not due to stem end rind breakdown or other peel disorders. Foliar application of potassium and 1% Vapor Gard reduced peel breakdown by 50% as compared to control fruit. In the table 23, peel breakdown and decay of Valencia orange is observed after 44 days of storage. These fruits were harvested 3 weeks after treatment application. Total decay and peel breakdown has increased irrespective of treatment applied in this week as compared to 2 week after treatment applicat ion(t able 22). Treatment of 1% Vapor Gard reduced peel breakdown by more than 50% as compared to control fruit.

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40 Table 22 Peel breakdown and decay of Valencia oranges after 44 days of storage under ambient conditions. The fruit were harvested on 10th June, 2009, 2 weeks after treatment application. Peel breakdown Treatment Sound Total decay General Total Control 47 28 ab 34 a 34 a 1% Vapor Gard 65 27 bc 15 c 15 c K 60 38 a 14 c 14 c Mg 65 17 c 22 bc 22 bc Foliar K + Mg 56 27 bc 27 ab 28 ab p value 0.0578 .0069 0.0065 0.0075 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P Table 23 Peel breakdown and decay of Valencia oranges after 44 days of storage under ambient conditions. The fruit were harvested on 17th June, 2009, 3 weeks after treatment application. Treatment Sound Total decay Total breakdown Control 50 bc 26 37 a Foliar K 47 c 31 36 a Foliar Mg 59 ab 15 31 ab Foliar K + Mg 54 bc 28 29 ab 1% Vapor Gard 66 a 24 16 b p value 0.0143 0.2384 0.028 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P 0.05. Experiment 2 In the first harvest on 04th December,2009 after 2 weeks of treatment showed no peel breakdown at all even af ter 46 days of treatment (Data not shown here). Interestingly, there was not much decay as well after long durations of storage of this fruit. This trend was also observed in other fruits harvested at week 3, week 4 and week 6 harvests in

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41 this block ( Data not shown here). This could be due to the season of harvest. These fruits were harvested early in the season. The weather around the month of harvest can also be a factor in negligible peel breakdown and decay in this experiment. Experiment 3 In this experiment, the treatments vapor guard 2% and Foliar K + Mg + Vapor guard 1% showed the highest reductions in peel breakdown compar ed to untreated fruit. In the 3rd week after harvest, an interesting trend was observed with most of the peel breakdown being manifested on the fruit after approximately 25 days of storage and even when the fruits were stored till 63 days, the total peel breakdown percentage did not increase more than 2% in all the treatments (t able 24 and 25) The decay percentage of fruits increased in the meantime. This trend cont inued in other harvests as well ( data not shown here). In the table 24, peel breakdown and decay of Marsh white grapefruit after 25 days of storage is observed. Foliar K + Mg + 1% Vapor Gard showed no peel breakdown at all. Vapor Gard 2% showed 8 times less peel breakdown than control fruit. Hence, Vapor Gard has consistently shown its effectiveness to reduce peel breakdown and can be recommended to growers for reducing peel breakdown. In the table 25, Peel breakdown and decay of Marsh white grapefruit after 63 days of storage under ambient conditions is observed. The fruit were harvested 3 weeks after treatment application. Foliar K + Mg + 1% Vapor Gard and Vapor Gard 2% showed 9 times less peel breakdown than control fruit. Also, even after 63 days of storage, peel breakdown in fruits irrespective of treatment did not increase by m ore than 2% as compared to 25 days of storage. It can be possible that peel breakdown incidence is manifested till a certain period of time after harvest.

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42 Table 24 Peel breakdown and decay of Marsh white grapefruit after 25 days of storage under ambient conditions. The fruit were harvested on 19th Feb, 2010, 3 weeks after treatment application. Treatment Sound Total Decay Total breakdown Mg 80 5 bdc 13 Vapor Gard1% 87 3 dc 9 K application 85 1 d 12 Control 79 3 bdc 16 Foliar K + Mg 83 7 bac 8 Vapor Gard2% 90 7 bac 2 Foliar K + Mg+ 1% Vapor Gard 89 10 a 0 Miller cocktail 86 8 ba 5 p value 0.8347 0.015 0.223 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P Table 25 Peel breakdown and decay of Marsh white grapefruit after 63 days of storage under ambient conditions. The fruit were harvested on 19th Feb, 2010, 3 weeks after treatment application. Treatment Sound Total Decay Total breakdown Mg 51 37 16 a Vapor Gard1% 59 34 12 ba K application 56 37 13 ba Control 48 46 18 a Foliar K + Mg 46 50 12 ba Vapor Gard2% 65 33 2 b Foliar K + Mg+ 1% Vapor Gard 56 42 2 b Miller cocktail 50 40 13 ba p value 0.0801 0.1594 0.0056 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P Experiment 4 In this experiment, similar trend was followed with most of the peel breakdown being ma nifested in the first 30 days of storage in Ruby red grapefruit and not much change

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43 in the percentage of peel breakdown even after prolonged durations of storage ( t able 26 and 2 7 ) The treatment Vapor Gard 2% showed the maximum reduction in peel breakdown. The average reduc tion in peel breakdown was 86% followed by foliar K + Mg + Vapor Gard1%, whic h had an average reduction 69%. In the table 26, peel breakdown and decay of Ruby red grapefruit after 31 days of storage was observed in 1 week af ter treatment application with 2% Vapor Gard showing 6 times less reduction than control fruit In the table 27, peel breakdown and decay of Ruby red grapefruit after 59 days of storage was observed in 1 week after treatment application with 2% Vapor G ard showing 5 times less reduction than control fruit. Diplodia was the main reason for decay in the experiment. Table 26 Peel breakdown and decay of Ruby red grapefruit after 31 days of storage under ambient conditions. The fruit were harvested on 05th March, 2010, 1 week after treatment application. Treatment Sound Total Decay Total breakdown Mg 62 12 29 ba Vapor Gard1% 79 21 21 ba K application 62 21 16 bac Control 56 16 31 a Foliar K + Mg 51 27 24 ba Vapor Gard2% 79 14 5 c Foliar K + Mg+ 1% Vapor Gard 62 27 13 bc Miller cocktail 60 22 22 ba p value 0.1174 0.0906 0.0185 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P

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44 Table 27 Peel breakdown and decay of Ruby red grapefruit after 59 days of storage under ambient conditions. The fruit were harvested on 05th March, 2010, 1 week after treatment application. Treatment Sound Total Decay Total breakdown Mg 41 ba 46 d 29 ba Vapor Gard1% 37 bac 52 bdac 21 ba K application 33 bc 61 ba 16 bac Control 35 bc 48 a 31 a Foliar K + Mg 24 c 61 a 24 ba Vapor Gard2% 48 a 49 bdac 6 c Foliar K + Mg+ 1% Vapor Gard 34 bc 60 bac 13 bc Miller cocktail 39 ba 54 bdac 23 ba p value 0.0189 0.041 0.0271 Values within each column followed by different letters are significantly different by Duncans multiple range test at P Significant at P Experiment 5 In this experiment, there was 96% average reduction in peel breakdown in Sugarbelle mandarin hybrid from the treatment foliar K + Mg but the data was not significant ( d ata not shown here).

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45 CHAPTER 3 POSTHARVEST FACTORS AFFECTING PEEL BREAKDOWN OF WHITE GRAPEFRUIT Introduction Postharvest factors including humidity, storage time, and storage temperature are critical to achieve maximum quality of a fresh horticultural commodity. Other researchers have shown that peel breakdown of fresh citrus may be reduced by maintaining high relative humidity during storage and shipping (Ben Yehoshua et al., 2001; Porat et al., 2004)., Citrus fruit can develop peel pitting even after relatively brief (3 hours) exposure to low (30%) relative humidity (RH) followed by high (90%) RH after harvest ( Alferez and Burns, 2004). During the 200607 and 200708 seasons, peel breakdown was relatively severe on fresh Florida citrus fruit. The disorder did not appear to be caused by chilling injury (CI) or postharvest pitting (Petracek et al., 1995), two of t he most common causes of peel breakdown in citrus. In the winter months, especially after cool and/or windy weather, symptoms of peel pitting and areas of peel necrosis were observed that progressed into stem end rind breakdown as the season progressed int o spring with warmer temperatures and when trees were flushing/flowering. Peel breakdown of Fortune mandarin under cool and low RH conditions was previously reported (Agusti et al., 1997; Vercher et al 1994), but these reports suggested the temperature was cold enough to cause CI. As previously stated, CI was likely not the cause of the Florida peel disorder. Hence, the need to investigate the possible cause(s) and best preventative measure(s) for the Florida disorder. Anecdotal reports suggested that inclusion of thiabendazole (TBZ) or Imazalil may reduce postharvest peel breakdown of citrus. While fungicides would not be expected to affect

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46 a physiological disorder, the current experiments included treatments containing TBZ or Imazalil to evaluate any possible effects. Increased peel breakdown has also been observed after incomplete rinsing of detergent from the fruit (Petracek et al., 2006). Thus, the objective of these experiments was to evaluate the effect of exposing fruit to low (30%) and medium (60% ) RH environments and different packingline handling treatments (i.e., not rinsing detergent from the fruit or inclusion of a fungicide in with the wax coating) on the development of postharvest peel breakdown of fresh citrus fruit. Materials and Methods Fruit Two separate harvests of Marsh white grapefruit were performed in Vero Beach, Florida on 26 January and 16 February 2009. Healthy white grapefruit were randomly harvested from every part of the tree at the height of 1 to 2 meters above ground level. The trees were healthy and the grove received standard commercial care. These fruits were transported to Indian River Research and Education Center in Fort Pierce, Florida on the day of harvest for postharvest treatment. Humidity Treatments After harvesting, fruits were kept in plastic crates at different humidity conditions i.e. 30% RH, 60% RH and 95% RH for 3 days at ambient temperature of approximately 73 F. Then different packingline treatments were a dministered before storing the fruit under ambient conditions of approximately 23oC and evaluating weekly for decay and the development of peel and other physiological disorders. Unless otherwise stated, all fruit were washed with a detergent, briefly drie d, and then coated with carnauba wax (JBT FoodTech,

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47 Lakeland, fla.) before final drying. The standard packingline procedures were altered depending on the treatment. Tr eatments are listed below (table 31) A dehumidifier was used to maintain 30% RH, whereas the laboratory environment maintains approximately 60% RH. Wet rags were placed on fruit crate tops in the 95% RH environment to maintain high RH levels. Dataloggers were used to measure air temperatures and RH. A completely randomized design was used. Each treatment had four replicates of fifty fruits. Table 31. Different humidity and packingline treatment given to Marsh white grapefruit were performed in Vero Beach, Florida on 26th January and 16 February 2009. Treatment no. Initial storage RH (%) Changes to packingline handling 1 30 None 2 60 None 3 90 None 4 95 2000 ppm TBZ 5 95 2000 ppm Imazlil 6 95 Wash but no wax 7 95 No rinse or wax Decay and Peel B reakdown Decay and peel breakdown was visually evaluated on each fruit weekly and the percentage of fruit showing any decay or peel breakdown was calculated. Decayed fruits were discarded after each evaluation and evaluations were discontinued after about 50% of the fruits had decayed. Weight L oss To measure weight loss, ten fruits were weighed from each replicate at harvest, after going over packing line, and after 7, 14 and 21 days of storage. Values are expressed as percent weight lost per day.

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48 Statistical Analysis Percentage data was transformed to arcsine values and all data were analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS Institute Inc, Cary, N.C.). When differences were significant (P < 0.05), individual treatment means were separated using Duncans mul tiple range tests (P = 0.05). Results and Discussion Holding fruit for 3 days at different RH significantly affected subsequent peel breakdown during storage for 25 (Figure 31) or 45 (Fig. 32) days. Unwaxed fruits that were kept at 95% RH in prestorage developed approximately twice the peel breakdown of nonrinsed, unwaxed fruits after 25 days of storage. Fruits, kept at 30% RH in prestorage showed approximately eight times and five times more peel breakdown than fruits kept at 60% RH in prestorage after 25 and 45 days of storage respectively (Figure 3.1 and 3.2). Alferez et al., (2005) reported that Florida citrus can have peel pitting disorder due to sudden changes in relative humidity after harvest. Fruits kept at 30% RH received such sudden change in relative humidity. No significant difference was observed between waxed fruits prestored at 60% RH, prestored at 95% RH and prestored at 95% RH (with 2000 ppm TBZ + wax) (Figure 3.1 and 3.2). Fruits treated with wax and 2000 ppm Imazalil, which were kept at 95% RH in prestorage showed approximately seven times and four times less peel breakdown than fruits kept at 95% RH in prestorage after 25 and 45 days of

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49 storage respectively (Figure 3 1 and 3 2). Ben Yehoshua et al. (2001) had reported that peel breakdown incidence may be reduced by maintaining high relative humidity during storage but in our study, keeping fruits at high humidity did not reduce peel breakdown significantly compared to holding at 60% RH. Interestingly, in this first experiment, inclusion of Imazalil in the wax significantly reduced postharvest peel breakdown, whereas inclusion of a different fungicide (TBZ) did not. For the fruits harvested on 26th January, significant difference in total peel breakdown was again observed among treatment s after 24 and 52 days of storage (Figure 33 and 34). Fruits kept at 30% RH during prestorage showed about four times and three times more peel breakdown than fruits kept at 60% RH prestorage after 24 and 52 days of storage, respectively (Figure 33 and 3 4). In this experiment, neither fruits treated with 2000 ppm Imazalil nor TBZ showed any significant reduction in peel breakdown (Figure 33 and 34). Hence, Imazlil and TBZ are not effective in reducing peel breakdown consistently The fruit lost water gradually during storage, with fruit prestored at 30% RH loosing significantly more water that fruit prestored at 60%, which in tern lost water significantly faster that fruit stored at 95% RH (Table 32 ). These differences became insignificant as storage time progressed and the initial water loss became a smaller fraction of total water loss. The fact that water loss was slowest after prestorage at 95% RH concurs with previous research showing that RH should be maintained as high as possible to keep cit rus fruit fresh and

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50 turgid (Ritenour et al., 2003). There was significant effect of different treatments on decay caused in fruits harvested on 26th January by diplodia and penicillium (Table 33 and 34 ). Unwaxed fruits, which were kept at 95% RH in prest orage showed approximately three times and 1.5 times more decay than nonrinsed, unwaxed fruits kept at 95% RH in prestorage after 24 and 52 days of storage respectively (Table 33 and 34 ). Waxed fruits, which were kept at 30% RH in prestorage showed appr oximately three times more decay than fruits kept at 60% RH in prestorage after 24 and 52 days of storage (Table 33 and 34 ). Fruits prestored at 95% RH showed four times less decay than fruits kept at 60% RH in prestorage after 24 days of storage but no significant difference after 52 days of storage. Fruits treated with wax and 2000 ppm Imazalil showed three times more decay than fruits treated with 2000 ppm TBZ after 52 days. Fungi cause the most serious decay in citrus in Florida and warm, humid clima te of Florida exacerbates the incidence. The most common postharvest fungus diseases of Florida citrus are Diplodia stem end rot (Lasiodiplodia theobromae), green mold (Penicillium digitatum), sour rot (Galactomyces citri aurantii) and anthracnose (Colletotrichum gloeosporioides) (Ritenour et al., 2003). Alternaria stem end rot (black rot) (Alternaria citri) and brown rot (Phytophthora palmivora and P. nicotianae) are less frequent in the state of Florida, but may cause substantial losses in some seasons. C itrus fruit stored at low relative humidity after harvest are more likely to decay. Low RH causes stress that promotes peel breakdown and increased

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51 peel breakdown can lead to increased decay (which has been described in detail in the earlier chapter). Appl ication of a wax coating and fruit storage and rapid handling at high humidity retards desiccation and maintains fruit turgidity and freshness compared to washed but not waxed fruit, but not necessarily unwashed fruit. Hence, it helps in reducing suscepti bility to green mold and stem end rind breakdown, thereby, making the fruit less susceptible to decay. Relative humidity should be 90 to 98% for fruits held in wooden/plastic containers and 8590% in fiberboard cartons to prevent the deterioration of carto n (Ritenour et al., 2003). Thiabendazole (TBZ) is a benzimidazole fungicide and is effective against Lasiodiplodia theobromae and Penicillium digitatum. It is applied with bin drenchers and on the packinghouse line. TBZ should be applied at a concentration of 1,000 ppm (0.1%) as a water suspension or at 2,000 ppm (0.2%) in a water based wax (Ritenour et al., 2003). Imazalil is very effective against Penicillium digitatum but not much for control of Lasiodiplodia theobromae and it is ineffective against Phy tophthora palmivora and Galactomyces citri aurantii. Imazalil should be applied at 1,000 ppm (0.1%) as a water suspension or at 2,000 ppm (0.2%) in a water base wax (Ritenour et al., 2003). Significant effect of different treatments on decay was observed i n fruits harvested on 16th February by diplodia and penicillium (Table 35 and 36 ). Unwaxed fruits, which were kept at 95% RH in prestorage showed approximately two times less decay than nonrinsed, unwaxed fruits kept at 95%

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52 RH in prestorage after 24 day s of storage (Table 3 5 ). This result is different from the trend observed in the previous harvest. Waxed fruits, which were kept at 30% RH in prestorage showed approximately three times and 1.5 times more decay than fruits kept at 60% RH in prestorage af ter 24 and 52 days of storage respectively (Table 35 and 36 ). Fruits prestored at 95% RH showed 2.5 times and 1.5 times more decay than fruits kept at 60% RH in prestorage after 24 and 52 days of storage respectively. This result is different from the tr end observed in the previous harvest. Fruits treated with wax and 2000 ppm Imazalil showed 1.5 times less decay than fruits treated with 2000 ppm TBZ after 52 days (Table 3 5 and 36 ). The results showed TBZ and Imazlil reduced green mould significantly w hich concurs with the previous study done by Ritenour et al., (2003).

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53 Figure 31. Total peel breakdown (%) of white grapefruit harvested on 16February after 25 days of storage. Bars with different letters are significantly different by Duncans multiple range test at P

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54 Figure 32. Total peel breakdown (%) of white grapefruit harvested on 16 February after 45 days of storage. Bars with different letters are significantly different by Duncans multiple range test at P

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55 Figure 3 3. Total peel breakdown (%) of white grapefruit harvested on 26 January after 24 days of storage. Bars with different letters are significantly different by Duncans multiple range test at P

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56 Figure 34. Total peel breakdown (%) of white grapefr uit harvested on 26 January after 52 days of storage. Bars with different letters are significantly different by Duncans multiple range test at P Table 32 Weight loss in white grapefruit harvested on 26 January after 2, 7, 14 and 21 days of storage at respective relative humidity Different letters are significantly different by Duncans multiple range tests at P Pre Storage RH (%) 2 Days Wt. Loss % 7 Days Wt. Loss % 14 Days Wt. Loss % 21 Days Wt. Loss % 30 1.4 a 2.0 a 3.5 a 4.8 a 60 0.9 b 1.9 a 3.4 a 4.7 a 95 0.1 c 1.7a 3.0 b 4.3 b

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57 Table 33 Decay (%) of white grapefruit harvested on 26 January after 24 days of storage Different letters are significantly different by Duncans multiple range test at P Pre Storage RH(%) Packingline Treatment Healthy% Total decay% Total Breakdown (%) 30 Wax 50 b 6 a 46 a 60 Wax 85 a 2bc 12 b 95 Wax 93 a 0 c 6 b 95 2000 ppm TBZ + Wax 97 a 0 bc 1 b 95 2000 ppm IMZ + Wax 91 a 1 bc 6 b 95 No Wax 86 a 4 ab 10 b 95 No Rinse or Wax 94 a 1 bc 3 b P Value <.0001 0.0193 0.0002 Table 34 Decay (%) of white grapefruit harvested on 26 January after 52 days of storage Different letters are significantly different by Duncans multiple range test at P 0.05. Pre Storage RH(%) Packingline Treatment Healthy% Total decay% Total Breakdown (%) 30 Wax 27 c 24 a 71 a 60 Wax 67 ab 9 bc 24 b 95 Wax 68 ab 12 bc 14 b 95 2000 ppm TBZ + Wax 87 a 2 d 10 b 95 2000 ppm IMZ + Wax 64 b 7 cd 28 b 95 No Wax 59 b 14 b 27 b 95 No Rinse or Wax 68 ab 9 bc 22 b P Value 0.0004 <.0001 0.0002

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58 Table 35 Decay (%) of white grapefruit harvested on 16thFebruary after 25 days of storage Different letters are significantly different by Duncans multiple range test at P 0.05. Pre Storage RH (%) Packingline Treatment Healthy% Total decay% Total Breakdown (%) 30 Wax 51 c 9 a 43 a 60 Wax 92 a 2 c 5 c 95 Wax 89 ab 6 b 3 c 95 2000 ppm TBZ + Wax 92 a 0 c 5 c 95 2000 ppm IMZ + Wax 99 a 1 c 0 c 95 No Wax 77 b 2 c 19 b 95 No Rinse or Wax 86 ab 5 b 8 bc P Value <.0001 <.0001 <.0001 Table 36 .Decay (%) of white grapefruit harvested on 16thFebruary after 45 days of storage. Different letters are significantly different by Duncans multiple range test at P Pre Storage RH (%) Packingline Treatment Healthy% Total decay% Total Breakdown (%) 30 Wax 40 d 22 a 49 a 60 Wax 78 ab 14 bc 10 cd 95 Wax 69 bc 21 ab 10 cd 95 2000 ppm TBZ + Wax 76 abc 14 bc 9 cd 95 2000 ppm IMZ + Wax 89 a 8 c 2 d 95 No Wax 62 c 10 c 28 b 95 No Rinse or Wax 68 bc 13 bc 19 bc P Value <.0001 0.007 <.0001

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59 CHAPTER 4 EFFECT OF DIFFERENT COATINGS ON REDUCING FREEZE INJURY OF WHI TE GRAPEFRUIT Introduction While Florida is a subtropical environment with an excellent climate for growing high quality citrus, occasional cold fronts from the north can bring freezing temperatures in the winter season that may injure fruit and trees. The decade of the 1980s brought a set of severe freezes to Central Florida, killing many of the state's citrus trees and shifting the citrus growing region from north and central Florida to south Florida. Freezing temperatures affected a large portion of Florida's citrus growing areas in January 1981, January1982, D ecember 1983, January 1985, February 1989 and December 1989 (Miller, 1991).The citrus producing region of Florida experienced 8 days of subfreezing temperatures during January 513, 2010 (USDA Citrus Forecast March 2010). Symptoms of freezing injury are i nternal drying and free juice in the core. External symptoms of freeze damage on the fruit occur on the outer, sun exposed area which gets a pink pitting injury. Injury can begin with as little as 2 to 4 hours below 2.2oC. Frost injury in the grove predis poses grapefruit to alternaria stem end rot on fruit during storage (SchiffmannNadel et al., 1975). Citrus peel is less susceptible to freeze injury as compared to internal membranes and juice vesicles. Externally uninjured fruit can contain large areas of completely desiccated tissue, typically at the stem end of the fruit. As with most other blemishes, the extent of fruit damage permitted varies with local regulations (Grierson and Ting, 1978). Vapor Gard (Miller Chemical and Fertilizer,Hanover, Pa.), a n antitranspirant, is sold to retard transpiration and maintain healthy foliage. Antitranspirants are believed to act as barriers to external

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60 nucleators(Levitt, 1980). The antitranspirant film on the surface of the leaves should impede the frost that forms on the surface from providing a nucleator for water inside the plant. Earlier published results of antitranspirants use for reducing freeze injury have been variable. Dieback of coldstored sycamore (Platanusoccidentalis L.) seedlings was reduced after antitranspirant treatment whereas freeze damage to developing peach (PrunuspersicaBatsch) fruits (Matta et al., 1987; Rieger and Krewer, 1988) and young citrus trees (Burns, 1970, 1973) was not reduced by antitranspirant treatment. Carnauba wax (FMC Corporat ion, Lakeland, fla.) is a coating which is applied to citrus fruits for reducing weight loss from transpiration losses. We believed that its spray will impede frost by providing a protective layer over the fruit. The objective of this study was to evaluate the two commercially available materials (Vapor Gard and Carnauba wax) for frost and freeze protection of citrus trees under field conditions and their effect on peel breakdown of grapefruit. Materials and Methods Fruit Experiments were conducted on January 6th, 2010 at two commercial Marsh White grapefruit groves; one located west of Fort Pierce and the other in Vero Beach, Florida. Temperature was 20oC and wind speed was less than 5 meter per second from north to south on 6th January, 2010. Spraying operation was performed in the afternoon on 6th January, 2010. In the Fort Pierce block, Grapefruit trees were sprayed with either 1% or 5% Vapor Gard (Miller Chemical and Fertilizer,Hanover, Pa.) or 1:1 or 1:10 dilutions of carnauba wax(JBT Food techCorpor ation, Lakeland, fla.). Control trees were left unsprayed. The

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61 experiment was established in a randomized complete block design with each treatment having three replicates. Single tree replicates were used. Rows were oriented north and south. In the Vero block, grapefruit trees were sprayed by with either 1% or 5% carnauba wax or left unsprayed (control). In this block, each treatment had three replicates. Harvest and P ostharvest Operation: Fifty fruits were harvested per replicate on January 12, 2010 from both the experimental sites and brought to Indian River Research and Education Center at Fort Pierce, Florida on the same day. Fruit were placed in the postharvest lab floor (~23 oC, 5060% RH) for 3 days before washing and waxing with Carnauba wax. Fruits were cut in 1/12 in 1/4" slices for freeze injury detection according to the USDA procedure. Two fruits were cut open per replicate before washing and waxing and noted for any abnormalities. The remaining fruits from each replicate were washed and waxed and placed on the postharvest facility floor for evaluation. A freezing injury scale ranging from 1 (no freezing symptoms) to 9 (severe freezing symptoms), depending on the severity of freeze injury was used to visually evaluate the trees for freeze injury (figures 4 3 to 49 ). For example, tree with maximum leaves having severe freeze injury symptoms were given a rank of 9 in the scale. Wilting, leaf curl, necrosis and brown spots were used as symptoms of freeze injury in these evaluations. These four symptoms were combined together to observe the freeze injury incidence. Weight Loss Weight of 10 fruits per replicate was taken after washing and waxing and then again 15 days later.

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62 Statistical Analysis Percentage data (peel breakdown, decay) was transformed to arcsine values and all data was analyzed by analysis of variance using SAS (PROC GLM) for PC (SAS Institute Inc, Cary, N.C.). When differences were significant (P < 0.05), individual treatment means were separated using Duncans multiple range tests (P = 0.05). Results and Discussion After the freeze events, trees at the Vero block showed no signs of freeze injury (data not shown). However, freeze injury symptoms were observed at the Fort Pierce bl ock where minimum field temperatures dropped lower than in the Vero block (Figure 4 1 and 42 ). There was no significant difference between treatments with regard to freeze injury. Fruits were cut immediately after harvest with no visible internal or external injury. No freeze injury was found in fruit from the Vero block after 24 days storage (data not shown). Just a few fruit showed freeze damage from the Fort Pierce block after 24 days storage, but there were no significant difference between treatments (data not shown). Trees were evaluated for freeze scale and leaf wilting was less and the general condition of trees looked better than the first evaluat ion just after freeze (Table 41 and Table 42 ). The trees at Vero block showed no external freeze inj ury symptoms like wilted leaves (Data not shown here). External freeze injury symptoms were observed in Emerald block.

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63 Table 41.Fruit drop and tree injury of the Fort Pierce block evaluated on 14January, 2010. Tree injury rating is from 1 (no damage) t o 9 (severe damage). Treatment Fruit drop average Standard error Tree injury average Standard error Carnauba 1:1 7.3 2.4 2.3 0.3 Carnauba 1:10 7.0 0.5 4.0 0.0 Control 4.6 0.8 3.3 1.2 Vapor Gard1% 4.6 0.3 3.6 0.3 Vapor Gard5% 3.0 1.1 3.3 0.3 Table 42. Fruit drop and tree injury of the Fort Pierce block evaluated on 08February, 2010. Tree injury rating is from 1 (no damage) to 9 (severe damage). Treatment Fruit drop average Standard error Tree injury average Standard error Carnauba 1:1 12.0 2.5 3.3 0.3 Carnauba 1:10 11.3 2.1 4.0 0.0 Control 4.3 1.4 3.6 0.3 Vapor Gard1% 10.3 1.8 4.0 0.5 Vapor Gard5% 5.3 1.8 5.0 0.5

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64 Figure 41.Temperature and RH data from the data logger at Fort Pierce block in the week of harvest from 01/06/10 to 01/14/10.

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65 Figure 42. Temperature and RH data from the data logger at Vero block in the week of harvest from 01/06/10 to 01/14/10.

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66 Figure 43.Freeze injury (Number 9 on the freezing scale). Figure 44.Freeze injury (Number 8 on the freezing scale).

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67 Figure 45. Freeze injury (Number 7 on the freezing scale). Figure 46. Freeze injury (Number 5 on the freezing scale).

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68 Figure 47. Freeze injury (Number 4 on the freezing scale). Figure 48. Freeze injury (Number 3 on the freezing scale).

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69 Figure 49. Least severe freeze injury (Number 2 on the freezing scale).

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70 CHAPTER 5 CONCLUSION The research reported in this thesis has shown the effects of preharvest foliar potassium (K), magnesium (Mg), or Vapor Gard application, water deficit treatment, different postharvest humidity conditions and packingline treatments along with storage time in reducing peel breakdown of citrus. Two commercially available materials (Vapor Gard and carnauba wax) were evaluated for frost and freeze protection of citrus trees under field conditions.As a result of these studies, it was found that there was no si gnificant effect of Vapor Gard or Carnauba wax in reducing freeze injury but there was very little freeze injury to the fruit. Foliar applications of K, Mg, K + Mg and 1% Vapor Gard reduced peel breakdown in Valencia oranges compared to the control fruit in the month of May. 1% Vapor Gard showed the best results and can be recommended to growers for reducing peel breakdown in summer. There was increase in total decay with the increasing days of storage. In the first week of harvest after treatment, the peel breakdown was very less compared to other harvests. The white grapefruit harvested in December showed negligible peel breakdown even after long durations of storage. There was not much decay as well after long durations of storage of this fruit. Thi s can be possibly due to the effect of seasonal changes. Early season fruit is less susceptible to peel breakdown as compared to late season fruit. The effect of 2% Vapor Gard and the treatment foliar K + Mg + 1% Vapor Gard in reducing peel breakdown in white grapefruit was very important. In the 3rd week after harvest, an interesting trend was observed with most of the peel breakdown being

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71 manifested on the fruit after approximately 25 days of storage and even when the fruits were stored till 63 days, the total peel breakdown percentage did not increase more than 2% in all the treatments. Hence, there is a possibility that peel breakdown manifestation is dependent on particular time of storage. In red grapefruit, similar trend was followed with most of the peel breakdown being manifested in the first 30 days of storage. The treatment 2% Vapor Gard showed the maximum reduction in peel breakdown. Hence, the treatment 2% Vapor Gard can be recommended to reduce peel breakdown in red grapefruit. Significant d ifferences in postharvest treatments with respect to total peel breakdown were observed after different durations of storage. After long duration of stora ge at ambient conditions, shelf life of fruit held for 2 to 3 days at 30% RH was reduced by developed about three to eight times more than fruit held at 60% RH Hence, fruits kept at 30% RH received sudden change in relative humidi ty causing more peel breakdown. Fruits treated with wax and 2000 ppm Imazalil showed inconsistent results in reducing peel breakdown. Water loss in the fruit showed gradual losses in every treatment after every evaluation. The relative differences in weight loss reduced among fruits prestored at 30%, 60% and 95% RH for 3 days over longer storage durations. The lowest looses in water were at 95% RH. The results showed TBZ and Imazalil reduced green mould significantly. Previous results have also shown their effectiveness in reducing postharvest decay. Hence, they can be recommended to packers.

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72 LIST OF REFERENCES Achilea O., 2000. Citrus and tomato quality is improved by optimized K nutrition. In: Improved crop quality by nutrient management, (Eds.) D. Anac& P. MartinPrevel.Kluwer Academic Publishers. pp: 1922. Agusti, M., Almela V., Zaragoza S., Gazzola R., and Primo Millo E 1997.Alleviation of peel pitting of 'Fortune' mandarin by the polyterpenepinolene. J. Hort. Sci. 653658. Agusti, M. 1999. Preharvest factors affecting postharvest quality of citrus fruit, pp. 134 In Advances in Postharvest Diseases and Disorder s Control of Citrus Fruit, M. Schirra (Editor). Alan H., Effie P., David M., Tom S. and Ron M 2001. Economic impact of floridas citrus industry, 19992000.University of Florida, Institute of Food and Agricultural Sciences,Food and Resource Economics Department, Gainesville, Florida. Economic Information Report 012. July 2001 Albrigo, L., Brown G.and Fellers P .1970.Peel and internal quality of oranges as influenced by grove applications of pinolene and Benlate.Proc. Fla. St.Hort. Soc. 83:26367. Albrigo L. and Grosser, J. 1996. Methods for evaluation of spray chemical phytotoxicity to citrus. Proc. Fla. State Hort. Soc. 109, 5257. Alferez F. and Zacarias, L. 2001. Postharvest pitting in navel oranges at nonchilling temperature: influence of rel ative humidity. Acta Hort. 553, 307308. Alferez F and J. Burns. 2004. Postharvest peel pitting at nonchilling temperatures in grapefruit is promoted by changes from low to high relative humidity during storage. Postharvest Biol. Technol. 32:7887. A lferez F., Zacarias, L. and Burns, J., 2005. Low relative humidity at harvest and before storage at high humidity influence the severity of postharvest peel pitting in Citrus fruit. J. Amer. Soc. Hort. Sci. 130:225231. Allen M 2000.History of Florida Citrus, Florida Grower Magazine, August, 2000, Meister Publishing Company, Willoughby, OH. Bar Akiva A., 1975 Effect of foliar application of nutrients on creasing of 'Valencia' oranges. HortScience 10, 6970 Ben Yehoshua S., Peretz J., Moran R., LavieB.a nd Kim J. 2001. Reducing the incidence of superficial flavedo necrosis (noxan) of Shamouti oranges (Citrus sinensis, Osbeck), Postharvest Biol. Technol. 22 (2001), pp. 19 27 Berkowitz, G. and Rabin J.,1988.Antitranspirant associated abscisic acid effects on the water relations and yield of transplanted bell peppers. Plant Physiol. 86:329331.

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73 B oman, B. 1997. Effectiveness of fall potassium sprays on enhancing grape fruit size. Proc. Fla. State Hort. Soc. 110:17. Boman, B. and Hebb, J., 1998. Pos t bloom and summer foliar K effects on grapefruit size. Proc. Fla. State Hort. Soc. 111:128135.6. Brooks, C. Bratley, C. and McColloch, L. 1936. Transit and storage diseases of fruits and vegetables as affected by initial carbon dioxide treatments USDA Tech. Bull. 519. Browning, W., McGovern, R. Jackson, L., Calvert, V. and Wardowski, W 1995. Florida Citrus Diagnostic Guide Florida Science Source, Longboat Key FL Burns, R.M. 1970. Testing foliar sprays for frost protection of young citrus.P roc. Fla. State Hort.Soc. 83:9295. Burns, R. 1970. Testing foliar sprays for frost protection of young citrus.Proc. Fla. State Hort.Soc. 83:92 95. Burns, R. 1973. Chemical sprays for protection of young trees. Citrograph 59:78, 22. Bryan, O. 1950. M alnutrition symptoms of citrus with practical methods of treatment Fla.State Dept. Agr. Bull. 93. Chace, W., Harding, P., Smoot, J.and Cubbedge, R. 1966. Factors affecting the quality of grapefruit exported from Florida. USDA Marketing Res. Rept. 739 Chapman, H. 1958. Citrus quality influenced by potassium. Calif. Citrograph 43:179181. Cronje P., Barry G.and Huysamer M. 2008. The Effect of Potassium, Calcium andMagnesium Foliar Applications on Postharvest Rind Breakdown of Nules Clementine Mandarin. ISC Congress abstract. D avenport D.,H agan R. andMartin P 1969. Antitranspirants: uses and effects on plant life. Calif. Agr. 23: 14 16. Dav is, P. and Hoffman, R. 1973. Reduction of chilling injury of citrus fruits in cold storage by intermittent warming. J. Food Sci. 38, 871873. Eaks I.1964. The effect of harvesting and packing house procedures on rind staining central California 'Washington' navel oranges. Proc.Am. Soc. Hort. Sci. 85, 245256. Eaks I.1969. Rind disorders of oranges and lemons in California. Proc. Int. Soc. Citriculture 3, 13431354

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74 Elmer H Brawner O .and Ewart, W. 1973. Scarring and silvering on Central Valley navels. Calif. Citrograph 58, 335338. EI Sharkawy, M., Abou Raya M.and Nagi M .,1976. Influence of Antitranspirants on leaf water content and transpiration of sunflower.Proceedings of the Third MPP Meeting. Iz mir October, 1975. Embelton, T., Jones W. and Platt R 1975. Plant nutrition and citrus fruit crop quality and yield. HortScience 10(1):4850. Erner Y., Kaplan B., Artzi B. and HamuM.,1993. Increasing citrus fruit size using auxins and potassium. Acta Hort. 329: 112116. Freeman, B., 1976. Artificial windbreaks and the reduction of windscar of citrus. Proc. Fla. State Hort. Soc. 89, 5254. Grierson, W. and Newhall, W., 1958.Sloughing. In Florida Guide to Citrus Insects, Diseases and Nutritional Di sorders in Color. R. M. Pratt (Editor). Fla. Agr.Exp. Stn. Grierson, W., 1965.Factors affecting postharvest market quality of citrus fruits, p. 6584. In: Proc. Amer. Soc. Hort. Sci., Carrib. Reg. XIII annual meeting, Kingston, Jamaica. Grierson, W.and Ting S., 1978. Quality control of fruit and products: Quality standards for citrus fruits, juices and beverages. Proc. Int. Soc. Citriculture, 2127. Grossenbacheru,J. G. 1941. Loose skinned tangerines. Proc. Fla. State Hort. Soc. 54, 44. Gu S., Fuchigami, H., Guak, S. and Shin, C. 1996. Effects of short term water stress, hydrophilic polymer amendment, and antitranspirant on stomatal status, transpiration, water loss, and growth in better boy tomato plants. J. Amer. Soc. Hort.Sci. 121:831 837. Hatton, T., Cubbedge, R.and Grierson, W. 1975. Some effects of prestorage, Hort. Rev. 4, 247271. carbondioxide treatments and delayed storage 'Marsh' grapefruit. Proc. Fla. State Hort. Soc. Hummel, R., 1990. Water relations of container grow nwoody and herbaceous plants following antitranspirant sprays.HortScience, 25: 726821. Levitt, J., 1980. High temperature stress (2nd edition), Responses of Plants to Environmental Stresses Vol. 1, Academic Press, London, pp. 347 470. Kavanagh. A. and Wood, R., 1967. The role of wounds in the infection of oranges byPenicillium digitatum Sacc. Ann. Appl. Biol. 60, 375383

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75 Kader, A. 1999. Fruit maturity, ripening, and quality relationships.Acta Hort.,485:203208. Kader, A., 2002. Postharvest technology of horticultural crops.3rd ed. Univ. Calif. Agr. Nat. Resources, Oakland, Publ. 3311. Ketchie, D. and Ballard, A. 1968. Environments which cause heat injury to 'Valencia' oranges. Proc. Am. Soc. Hort. Sci. 93, 166172. Klotz L 1975. W ater spot of navel oranges. Calif. Citrograph 60, 439441 Kuraoka, T. 1962. Histological studies on the fruit development of the satsuma orange with special reference to peel puffing. Memoirs, Ehime Univ. (Sect. VI) 8, 106154. Ladaniy a M., 2008. Citrus Fruit, Academic Press, San Diego, CA (2008). Lafuente, M. and Sala, J ., 2002.Abscisic acid and the influence of ethylene, humidity and temperature on the incidence of postharvest rindstaining of Navelina oranges (Citrus sinensis L. Osbeck) fruits. Postharvest Biol. Technol. 25, pp. 49 57 Lafuente, M. and Zacarias, L., 2006. Postharvest physiological disorders in citrus fruit, Stewart Postharvest Rev. 1 (2006), pp. 1 9. Matta, F., Little S.and Mullenax R 1987.Effects of two chemicals on peach fruit survival following late spring frosts Miss. Agr.For.Expt. Sta. Res. Rpt. vol. 12.p.18. Marella, R., 1999. Water Withdrawals, Use, Discharge, and Trends in Florida, 1995. Water Resources Investigations Report 994002. Tallahassee, FL: USGS. 1999. McCornack, A. and Grierson, W. 1965. Practical measures for control of stem end Rind breakdown of oranges Fla. Agr. Ext. Circ. 286. McCornack, A., 1966. Blossom end clearing of grapefruit Proc. Fla. State Hort. Sci. 79, 258264 McCornack, A., 1970. Peel injury of Florida navel oranges. Proc. Fla. State Hort. Soc 83 267270. Meir, S., Philosoph Hadas, S., Lurie, S., Dro by, S., Akerman, M., Zaubermana,G., Shapiro, B., Cohen, E.and Fuchs, Y. 1996. Reduction of chilling injury in storedavocado, grapefruit, and bell pepper by methyl jasmonate. Can. J. Bot. 74, 870874. Miller, K. 1991. Response of Florida citrus growers to the freezes of the 1980s.Climate Research 1:133144.

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76 National Agricultural Stat istics Service. 2009. Citrus Fruits 2009 Summary, U.S Dept. Agr. 24 September 2009. http://www.citrusandvegetable.com/ccmsdocuments/cit92409.pdf Nel,J., Jacobs, C.and Swarts, D 1974. Cold storage of citrus: Mechanical handling of fruit and its effect on rind disorders. 19641974. Dept.Agr. Tech. Serv. (South Africa), Agr. Res. 98, 9899. Nitzsche, P. Berkowitz G. andRabin, J 1991.Development of a seedlingappl ied antitranspirant formulation to enhance water status, growth and yield of transplanted bell pepper. J. Amer. Soc.Hort. Sci. 116:405--411. No rdby, H. and McDonald, R. 1990. Method for protecting citrus fruit from chilling injury and fruit protected thereby. U.S. Patent 4,921,715 Pantastico, E. Grierson, W. and Soule, J. 1966. Peel injury and rind color of 'Persian' limes as affected by harvesting and handling methods. Proc. Fla. State Hort. Sac. 79,338343. Petracek P.,Wardowski W.and Brown G. 1995. Pitting of grapefruit that resembles chilling injury.HortScience 30:14221426. Petraeck, P., Dou H. and Pao, S. 1998. The influence of applied waxes on postharvest physiological behaviour and pitting of grapefruit. Postharv est Biol. Technol. 14, 99106. Petracek, P. and Davis, C. 2000. Ultras true ture comparison of postharvest pitting, chill ing injury, and preharvest physical damage of white grapefruit peel. Proc. Intl. Soc. Citricult. IX Congr. 1079 1083. Petracek, P., Kelsey, D. and Grierson, W., 2006. Physiological peel disorders, p. 397419. In: W.F. Wardowski, W.M. Miller, D.J. Hall, and W. Grierson (eds.). Fresh citrus fruits, 2nd ed. Florida Science Source, Inc., Longboat Key, Fla. Plaut, Z., Magril Y. and Kedem, U., 2004. A new film forming material, which reduces water vapour conductance more than CO2 fixation in several horticultural crops, J. Hort. Sci. Biotechnol. 79 (2004), pp. 528 532. Porat R., Weiss, B., Cohen L., Daus A. and Aharoni N. 2004. Reduction of postharvest rind disorders in citrus fruit by modified atmosphere packaging, Postharvest Biol. Technol. 33 (2004), pp. 35 43 Prange, R. andDeEll, J., 1997. Preharvest factors affecting postharvest quality of berry crops, HortScience 32 (5) (1997), pp. 824 830.

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77 Raber D.,Soffer, Y. and Livne M., 1997. The effect of spraying with potassium nitrate on Nova fruit size.AlonHanotea 51: 382386, (in Hebrew). Rieger, M. and G. Krewer., 1988.Cryoprotectant and antitranspirant efficacy for fros t protection of Prunus flower ovaries. Proc. Fla. State Hort.Soc. 101:251253. Riehl, L. and C arman, G., 1953. Water spot on navel oranges. Calif. Citrograph 7, 78. Ritenour, M. and Dou, H., 2000. Factors contributing to the "green ring" disorder of fresh market citrus. Proc. Fla. State Hort. Soc. 113:297299. Ritenour, M. and Dou H 2003.Stem End Rind Breakdown of Citrus Fruit.IFAS Fact Sheet HS 936. http://edis.ifas.ufl.edu/HS193 Ritenour, M., Zhang, J.,Wardowski W.and Eldon Brow G 2003. Postharvest Decay Control Recommendations for Florida Citrus Fruit. IFAS Fact Sheet CIR359A. http://edis.ifas.ufl.edu/ch081 SchiffmannNadel, E. Chalutz, J. and Dagan M 1975. Reduction of chilling injury in grapefruit by thiabendazole and benomyl during longterm storage, J. Am. Soc. Hortic. Sci. 100 (1975), pp. 270 272. Schneider, H. 1968. The Anatomy of Citrus.The Citrus Industry, Volume II.185. University of California, Berkeley. Scott,F. and Baker, K., 1947. Anatomy of 'Washington' navel orange rind in relation to water spot. Bot. Gaz. 108, 459475. Smoot, J., Houck, L. and Johnson, H., 1971. Market diseases of citrus and other subtropical fruits. USDA Agr. Handbook 398. Soule, J. and Grierson, W., 1986.Maturity and grade standards. In: Fresh Citrus Fruits. W.F. Wardowski, S. Nagy, and W. Grierson (eds) AVI Pub. Co., CT, pp. 2348. Stelinski, L., Graham, J., Muraro ,R.andMorris R 2009. 2010 Florida Citrus Pest Management Guide: Management Options for Nonbearing Groves and Fresh or Processed Fruit. IFAS Fact Sheet CPMG02. http://edis.ifas.ufl.edu/cg034 Tamim M., Goldschmidt E., Goren A. and Shachnai A., 2000. Potassium reduces the incidence of superficial rind pitting (nuxan) on Shamouti orange. AlonHanotea 54: 152157, (in Hebrew). Tucker, D., 1978. Citrus irrigation management.Inst. Food Agr. Sci. Ext. Cir. 444. Univ. Fla.

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78 Turrell, F O rlando J. and Austin, S 1964. Researchers forge a link between rindoil spot and foggy weather. West. Fruit Grow. 18:1718. USDA Economic Research Service. 2010. Fruit and Tree Nuts Outlook/FTS 341/March 26, 2010.Economic Research Service, USDA. http://www.ers.usda.gov/Publications/FTS/2010/Mar03/FTS341.pdf Vakis, N., Grierson, W. and Soule, J ., 1970. Chilling injury in tropical and subtropical fruits. 111. The role of C02 in suppressing chilling injury of grapefruit and avocados. Proc. Trop. Reg., Am. Soc. Hort. Sci. 14, 89100. Vercher, R., Tadeo, F., Almela, V Zaragoza, S., PrimoMillo, E. and Agusti, M. 1994. Rind structure, epicuticular wax morphology and water permeability of 'For tune' mandarin fruits affected by peel pitting. Ann. Bot. 74, 619625 Wardowski, W., McCornack, A. and Grierson, W. 1976. Oil spotting (oleocello sis) of citrus fruit. Fla. Coop. Ext. Serv. Circ. 410.

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79 BIOGRAPHICAL SKETCH Sambhav was born in India. In 2008, he obtained his Bachelor of Science degree in h orticulture from the College of Agriculture, Pune in India. In 2008, he s tarted his masters program in horticulture at the University of Florida and successfully completed his degree in 2010.