• TABLE OF CONTENTS
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 Front Cover
 Title Page
 Table of Contents
 Introduction
 Materials and methods
 Results and observations
 Discussion
 Summary
 Literature cited














Title: effect of maturity, time of harvest, weather and storage conditions on the quality and deterioration of soybean seed by fungi in Florida
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Title: effect of maturity, time of harvest, weather and storage conditions on the quality and deterioration of soybean seed by fungi in Florida
Physical Description: Book
Creator: Alexander, L. J.
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1978
Copyright Date: 1978
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Volume ID: VID00001
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Table of Contents
    Front Cover
        Front Cover
    Title Page
        Title Page
    Table of Contents
        Table of Contents 1
        Table of Contents 2
    Introduction
        Page 1
        Page 2
    Materials and methods
        Page 3
    Results and observations
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
    Discussion
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Summary
        Page 18
        Page 19
    Literature cited
        Page 20
        Page 21
Full Text


DECEMBER 1978 BULLETIN 804 (TECHNICAL)





The Effect of Maturity, Time of Harvest,
Weather and Storage Conditions on the
Quality and Deterioration of Soybean
Seed By Fungi in Florida


Leonard J. Alexander, Phares Decker, and Kuell Hinson





















AGRICULTURAL EXPERIMENT STATIONS
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
UNIVERSITY OF FLORIDA, GAINESVILLE
E A. WOOD, DEAN FOR RESEARCH













THE EFFECT OF MATURITY TIME OF HARVEST, WEATHER AND
STORAGE CONDITIONS ON THE QUALITY AND DETERIORATION
OF SOYBEAN SEED BY FUNGI IN FLORIDA
BY
LEONARD J. ALEXANDER, PHARES DECKER, AND KUELL HINSON
Drs. Alexander and Decker, Visiting Professor and Professor, re-
spectively, Department of Plant Pathology; Dr. Hinson, 'Research
Agronomist, U.S. Dept. ofAgriculture, Agricultural Research Service,
Florida area, and Professor of Agronomy, Institute of Food and Ag-
ricultural Sciences, Gainesville, Florida.





















This public document was promulgated at an annual cost of
$1458.98 or a cost of 584 per copy to provide information to assist
in the production of high-quality soybean seed in Florida.















TABLE OF CONTENTS


Introduction ........................................... 1
Materials and Methods ..................................... 3
Results and Observations ................................. 4
Fungus infection and germination of seed ................... 4
Rainfall frequency in relation to soybean seed maturity and
harvest ............ .................... ................ 9
Evaluation of seed from commercial seed producers .......... 13
Discussion ........................................... 13
Summary ............................................... 18
Literature Cited ......................................... 20










THE EFFECT OF MATURITY TIME OF HARVEST, WEATHER AND
STORAGE CONDITIONS ON THE QUALITY AND DETERIORATION
OF SOYBEAN SEED BY FUNGI IN FLORIDA
BY
LEONARD J. ALEXANDER, PHARES DECKER, AND KUELL HINSON

Some researchers consider soybeans to be a difficult grain crop to
store without deterioration and loss of viability. However, Christensen
and associates (4, 5, 6, 9), who have done the most work on soybean
seed storage, did not support such a thesis. Their work showed that
soybeans which were properly harvested and dried did not deteriorate
and lose viability under Minnesota conditions.
Perhaps the reason that soybeans are considered difficult to store is
because several of the disease producing organisms are seed-borne (1,
2,8, 11, 13, 14, 15, 16, 18, 19,20,21,26,27,28,31,32). Lehman and Wolf
started their work on leaf, stem, and seed diseases of soybeans in the
United States about 50 years ago in North Carolina (18, 19,20,21,31,
32). Since the initial work of Lehman and Wolf there has been a long
series of papers on soybean diseases. Only those papers referring to
diseases incited by fungi, which are seed-borne or which affect ger-
mination, are referred to in this bulletin.
The time and method of infection of soybean seeds has not been elu-
cidated entirely for some of the more common and serious seed-borne
fungus diseases. This is especially true forDiaporthephaseolorum, in-
citant of pod and stem blight. Some workers (13,14,16) suspected, from
cultural studies of immature pod and beans, that the fungus is sys-
temic and invades the pod through the peduncle. From the data pre-
sented by these workers it appeared that systemic development
accounts for only a small percentage of seed infections. This low in-
cidence of infection is in contrast to the high incidence of seed infection
that occurred following delayed harvest (1, 2,10,18,27,30). Most severe
seed infection by fungi undoubtedly occurred from pod invasion.
The time of infection of plant parts by several organisms is uncer-
tain. Lehman (18) found evidence to support the view that Diaporthe
spp. of soybeans produced what he termed incipient lesions which ap-
peared to be dormant. Kmetz et al. (16) reported that they consistently
isolated Phomopsis spp., the imperfect stage of Diaporthe spp., from
immature stems of 31 cultivars and blends of field-grown soybeans.
Pathogens such as Colletotrichum infect hosts previous to maturity,
then remain dormant until the host approaches maturity. This has
been clearly shown for the pathogen Colletotrichum phomoides, the
incitant of anthracnose of tomato fruit. Such a situation can become
serious because healthy appearing fruits may be shipped to a fresh
market or a processing plant and be diseased a day or two later. Tiffany

1








(26) found that the pathogen Colletotrichum truncatum, which causes
anthracnose of soybeans, could be isolated from symptomless, appar-
ently healthy trifoliate leaves. Freehand sections demonstrated that
the mycelium was confined to epidermal cells. Such dormant types of
infection probably do not occur for all fungi pathogenic to soybeans but
they do occur for the two pathogens, Diaporthe spp. and Colletotrichum
truncatum, which cause severe diseases.
Crane and Crittenden (7) found a close relationship between the
length of the flowering period and infection by the fungus, Cercospora
kikuchii, which causes the purple stain disease of seed. In general, they
found that early maturing cultivars had longer blooming period than
did late-maturing cultivars. Also Kilpatrick and Hartwig (15) found
that planting seed of the cultivar Ogden late, July 15 and August 1,
tended to reduce the percentage of seed with purple stain. Late plant-
ing also greatly reduced the incidence of pod and stem blight caused
by Diaporthe spp.
Christensen (4) divided seed decaying fungi into two groups, (a) stor-
age fungi and (b) field fungi. The storage fungi are primarily species
of Aspergillus and Penicillium. These fungi have one characteristic in
common, that is, they can grow without free water, parasitizing seed
at low moisture content. These fungi are ubiquitous, but usually cause
the greatest damage when the seed is stored.
In contrast, the field fungi are usually species ofAlternaria, Clados-
porium, husarium, Helminthosporium, and in the case of soybeans, ad-
ditionally Diaporthe, Colletotrichum, and Cercospora. Others exist, but
they are thought to be of lesser importance. In general, to cause seed
decay, field fungi need a higher moisture content than storage fungi.
Unfortunately, moisture content of seeds essential for growth ofDia-
porthe, Colletotrichum, and Cercospora has not been studied
critically.
The fact that both storage fungi and field fungi cause soybean seed
deterioration in Florida makes it important to provide storage condi-
tions that will greatly minimize the growth and development of all
seed-deteriorating fungi. Because other workers (4, 5, 6, 9, 11, 22, 23,
25) have described in detail the storage conditions necessary to pre-
vent growth and development of storage fungi in soybean seed and
grain, no effort has been expended in this investigation on storage
fungi. Physical limitations prevented work with bacteria. Also it was
impossible to identify the many species of fungi cultured from in-
fected seed. Thus the data are presented as number or percent of seed
infected by fungi.
The purpose of the experiments reported here has been to assess the
environmental conditions that affect infection of soybean seed by field
fungi. The primary work included meteorological data during matu-


2








rity and harvest, time of harvest in relation to maturity, moisture con-
tent of beans at harvest and in storage, and pure cultures of beans to
determine internal seed infection by fungi.

MATERIALS AND METHODS
The data reported here were gathered duringthe years 1972 through
1975 inclusive. The conditions of storage of soybean seed by seed pro-
ducers were investigated during the winter of 1974-1975. Seed har-
vested from the Florida State Variety Tests was used to determine
effects of delayed harvest on fungal infection and seed germination.
Plots of each cultivar consisted of 4 rows, 19 feet (5.8 m) long and 36
inches (91.5 cm) apart. A border was cut and discarded from the ends
of the rows so that only 16 feet (4.9 m) of row was harvested. Rows 2
and 3 were used for yield tests. Rows 1 and 4 were harvested periodi-
cally for seed evaluation, culture, and germination studies.
Planting dates were June 27,1972; June 11, 1973; May 29,1974; and
May 29,1975. All plantings were made on Agronomy Farms, at Gaines-
ville, Florida. Usually 12 or more cultivars were included in the test,
but because of physical limitations, only selected cultivars were used
in this study. Examination of the seed in the laboratory for purple stain
symptoms was done under a 2X magnifier-illuminator. Culture and
germination tests were made within a few days after harvest. Cultures
were made on lima bean agar and incubated at room temperature, 60-
750 F (15.5-240 C). Five seeds were placed in 100 mm petri dishes. The
seed was surface sterilized in a 10 percent Chlorox solution (sodium
hypochlorite, 5.25%) for 3 minutes and placed directly on agar in petri
dishes. The concentration of the diluted sodium hypochlorite steriliz-
ing solution was 0.525 percent. Twenty seeds were cultured from each
replicate for each cultivar, using five seeds per petri plate. Readings
of the cultures were made after 5-7 days incubation. The total number
of seeds infected by fungi, number infected with the purple stain fun-
gus, number germinated healthy, and number germinated diseased
were recorded.
The moisture content of soybean seed was determined by vacuum
oven drying, at ca 520 C for 72 hours. Germination determinations
were made by placing 50 seeds on filter paper in 150x25 mm plastic
petri dishes. Sterile water was added as needed, but usually 8-10 ml
of water was added initially. Seed free of fungi, or nearly so, germi-
nated rapidly. Germination readings were made after 5-7 days.
When samples were collected from seedsmen, they were placed in
jars with rubber gaskets. Moisture determinations, and culture and
germination tests, as described above, were made as soon as possible
after sampling. Soybeans were judged to be mature when 95 percent
of the pods appeared yellow and dry.

3








Climatological data were secured from the Institute of Food and
Agricultural Sciences weather station, Agronomy Farm, and from
Climatological Data, Florida, published by U.S. Dept. of Commerce.
The distance plots were located from the weather station at Gaines-
ville varied from year to year but did not exceed 600 yards (548.4 m).

RESULTS AND OBSERVATIONS
The results of these observations are presented under the headings,
(a) fungus infection and germination of seed, (b) rainfall frequency in
relation to soybean seed maturity and harvest, and (c) evaluation of
seed from commercial seed producers.
FUNGUS INFECTION AND GERMINATION OF SEED
The data obtained for 1972 and 1974 are presented in Figures 1 and
2 and Table 1. The data for 1973 and 1975 are not presented because
they are similar to those of 1972 and 1974. In 1972, five harvests of
seed were made from two relatively early cultivars, one medium ma-
turity cultivar, and one late cultivar. Seed of the late maturing culti-
var, Jupiter, maturity group IX, was not sufficiently mature for harvest
until November 15. Seed infection by fungi increased rapidly after
maturity (Figure 1A). In fact, the greatest increase in fungal infection
took place between October 30 and November 8. During this period
rainfall occurred on October 28, and November 4, 6, and 7 (Table 1).
During the harvest period November 8-15, rainfall occurred on two
days, November 14 and 15. Since this rainfall was on the day of harvest
and the preceding day, it probably was unlikely that this rainfall af-
fected infection.
For the harvest period November 15-22, there was little rainfall and
little infection occurred. During the harvest period November 22-29,
rainfall occurred on three days and infection increased noticeably.
Observations indicate that rainfall during periods of cloudy weather
cause the most rapid seed deterioration.
The data secured for fungus seed infection and germination of seed
of four cultivars from the 1974 plots are shown in Figure 2. Except for
the cultivar Forrest, seed infection was relatively low and germination
was high. The cultivar Forrest matured September 24 and was first
sampled October 10. Rainfall was heavy in mid-September, before For-
rest matured. The other three cultivars matured on October 10 or later
during periods of low rainfall. Thus little fungus seed infection oc-
curred and germination was relatively high until November 15. The
last of November and first of December some rainfall occurred, and
seed infection increased and germination decreased. Very little seed
deterioration occurred with the three cultivars which matured after
October 1 (Table 1 and Figure 2). During the months of October and

4











TABLE 1. RAINFALL IN INCHES.
Total rainfall
Days Milli-
Month 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Inches meters

1972

September .01 .16 .02 .17 .16 .60 1.12 28.4
October T .06.19 .07 .04 .63 .99 25.1
November .16 1.84.37 T 1.07 .01 T .55.12 1.67.26 .37.85 7.27 184.7
December .12 .02.02 .23 .77.02 .971.80.01 .19 T 4.15 105.4

1974
September .15 T 1.56 .55.21.16.31.06 1.35 .43.02.63 1.07.42 .03 .32 T 7.27 184.7
October T .11 .80 T .91 23.1
November .11 .09 T .13 T .16 .54 1.03 26.2
December .47 T T .11.56 .09.57 1.79 .44 T T T T 4.03 102.4








A
100 .- .-- --'- -

SMATURITY
80 CULTIVAR DATE
t / JUPITER -............... 11/5
6 // COBB ----- 10/30
i y /HOOD -.- 10/1,
L 40 FORREST 10/8
W/
S/ 1 ...
i I
20 /



10/30 ,1/8 11/15 11122 11/29
HARVEST DATES
PERCENT FUNGUS INFECTED SEED


B
100t **...........................

S". MATURITY
80 .CULTIVAR DATE
"*. JUPITER .... ............... 11/5
| 60 O ./ '\ COBB ------- 10/30
L HOOD ------.... 10/11
Z 40 "\\ FORREST 10/8

L \\
0-
20 \



10/30 11/8 11/15 1122 11/29
HARVEST DATES
PERCENT SEED GERMINATION

Figure 1. Effect of delayed harvest on soybean seed deterioration,
Gainesville, 1972.


November 1974, there was 0.91 and 1.03 inches (23 and 26 mm), re-
spectively, of rainfall.
It could be inferred from Figures 1 and 2 that the early maturing
cultivars were more susceptible to infection of pod and seed rotting
fungi than were the late maturing cultivars. Other workers (7,24,30)
have made this suggestion. However, if seed deterioration of the two
cultivars, Cobb, a medium to late cultivar, maturity group VIII, and
Forrest, an early cultivar, maturity group V (Figures 1 and 2), is cor-


6









A
100.

.. "MATURITY
80g .' CULTIVAR DATE
z / COBB .................

S60 /' HAMPTON 266A ----- 10/25
z BRAGG 10/20

z 40 FORREST ... 9/24

2o ..... "
.... ..... ,"


10/10 10/25 11/25 12/4
HARVEST DATES
PERCENT FUNGUS INFECTED SEED


B
100

"^ "'. ""MATURITY
80 \ CULTIVAR DATE

S \ COBB ................. 10/31
S60 \ HAMPTON 266A ------ 10/25

S \ BRAGG 10/20
S40 FORREST --.-. 9/24
L\

20 "'"..


"0.
10/10 10/25 11/25 12/4
HARVEST DATES
PERCENT SEED GERMINATION

Figure 2. Effect of delayed harvest on soybean seed deterioration,
Gainesville, 1974.

related with the rainfall for the years 1972 and 1974 (Table 1), it be-
comes apparent that rainfall has a more pronounced influence on
fungal seed infection than does cultivar. In 1972 seeds of the cultivar
Forrest, maturity date October 8, were 40 percent infected with fungi
on the harvest date of October 30, but did not become 97 percent in-
fected until November 29, 55 days after maturity. In contrast, seeds of
the cultivar Cobb were 100 percent infected November 29,30 days after
maturity. Little rainfall occurred from October 6 to October 28 (Table


7











TABLE 2.--RAINFALL, BY MONTHS, FOR THE SOYBEAN GROWING SEASONS 1972-75 INCLUSIVE, GAINESVILLE.
Months
June July August September October November
Milli- Milli- Milli- Milli- Milli- Milli-
Years Inches meters Inches meters Inches meters Inches meters Inches meters Inches meters
1972 11.24 285.5 1.49 37.8 3.76 95.5 11.42 290.1 1.12 28.4 4.63 117.6
1973 7.33 186.2 4.51 114.6 4.13 104.9 4.09 103.9 1.12 28.4 0.71 18.0
1974 10.05 255.3 7.38 187.5 7.50 190.5 7.54 191.5 0.11 2.8 1.29 32.8
1975 4.83 122.7 6.53 165.9 4.21 106.9 9.68 245.9 5.69 144.5 1.78 45.2



TABLE 3. -COMPARATIVE PERCENTAGE INFECTION OF PURPLE STAIN IN SEED OF FIVE SELECTED CULTIVARS OF SOYBEANS AS
DETERMINED BY VISUAL INSPECTION AND BY PURE CULTURE STUDIES. GAINESVILLE, 19751.
Harvest dates
Cultivars Maturity 10/16 10/27 11/14 12/1
Group
Group Visual Culture Visual Culture Visual Culture Visual Culture
Tracy VI 2.7 6.7 2.3 5.0 1.3 3.3 2.7 5.0
Centennial VI 1.0 15.0 3.7 21.7 3.7 13.3 5.0 1.7
Bragg VII 3.0 25.0 2.7 21.7 3.0 10.0 3.3 3.3
Hardee VIII 2.3 5.0 0.0 5.0 0.0 5.0 0.0 10.0
Cobb2 VIII 1.0 5.0 0.3 5.0 1.0 11.7 1.0 5.0
'One hundred seeds were used for each visual determination and 20 seeds were used for each pure culture determination.
2The variety Cobb was not completely mature at first harvest







1), whereas a rainy period began November 4, during which the cul-
tivar Cobb matured.
Likewise, in 1974, the seed ofForrest, which matured September 24,
reached a high level of fungus infection, whereas the seed of Cobb,
which matured October 31, did not. In the fall of 1974 rainfall was
relatively heavy (Table 1) until September 20, then declined sharply,
followed by low rainfall during October and November. Thus, the cul-
tivar Forrest matured shortly after a relatively high rainfall period,
whereas the cultivar Cobb matured in a dry period.
Additional evidence that there is little, if any, relationship between
susceptibility to fungal infection of soybean seed and date of maturity
is found in graphs (Figure 3) for fungal infection and the rainfall data
(Table 1). In the years 1972 and 1975, fungal infection was similar for
all cultivars. In those years (Table 2), rainfall was heavy during Sep-
tember and less in October. In the years 1973 and 1974, infections of
the early cultivar Forrest were much greater than the other four cul-
tivars; however, the maturity dates for Forrest were September 29 and
September 24, respectively, during or shortly after periods of frequent
rainfall. The other cultivars matured in October during periods of rel-
atively low rainfall.
Pure culture studies of seed have confirmed that it is impossible to
determine visually the amount of infection by fungi. This is illustrated
by the data obtained from five cultivars grown in the 1975 State Va-
riety Trials (Table 3). Visual counts for purple stain infection caused
by the fungus Cercospora kikuchii were made with a 2X magnifier-
illuminator. One hundred seeds were examined for each determina-
tion. Cultural determinations for purple stain infection were made as
described in methods and materials for other fungi. From the data in
Table 3, the actual amount of seed infection was found to be several
times the amount that can be detected by visual inspection. In fact,
cultures revealed infection 15 times greater than the amount deter-
mined by the visual method, with the October harvest of the cultivar
Centennial.

RAINFALL FREQUENCY IN RELATION TO SOYBEAN SEED MATURITY
AND HARVEST
A study was made to determine what chances exist for the produc-
tion in Florida of soybean seed without occurrence of rainfall between
harvest and maturity. The average monthly rainfall at four selected
locations, for the 40-year period of 1935-1974, is plotted in Figure 4.
The greatest amount of rainfall occurred during June, July, and Au-
gust, and the least rainfall occurred during the months of October and
November. The least rainfall at Gainesville and Avon Park occurred
during the month of November.

9











100 --*

90 ''*
I 1972
80 *
S7' MATURITY
o 70- CULTIVAR DATE

U 60- FORREST *************** 10

z50 \ HOOD 10/11
S40 / HARDEE ------- 10/27

0a. I
W 30. COBB 10/3IO
20-

I0-
O0
-10 0 10 20 30 40 50 60 70
DAYS AFTER MATURITY





100

90 1973
80 .* MATURITY
CULTIVAR DATE
z 70
o- ." FORREST ............* 9/29
u 60
"LL BRAGG 10/14
z 50 .
4 HARDEE ------- 10/22
z 40
U COBB 10/25
i 30-
a-
20-

10

-10 0 10 20 30 40 50 60 70
DAYS AFTER MATURITY

Figure 3. Percent infection of several cultivars of soybean seed by fungi
at varying numbers of days between harvest and maturity.


10










100
90 .......* .***.....
."** 1974
80 .'
so
MATURITY
z 70 CULTIVAR DATE

S 60 FORREST .................. 9/24

50 BRAGG ...-10/20

z 40 / HAMPTON 266A ----- 10/24

S30 / COBB --10/30
a-
20

0

"-10 0 10 20 30 40 50 60 70
DAYS AFTER MATURITY





100

90
.-.-.-.
80 *.. '..**"'* 1975

70 // MATURITY
S* CULTIVAR DATE
m60
0- / TRACY ................... 10/14
-50 /
- // CENTENNIAL -----*-* 10/10
2 40 /
S BRAGG ------ io/18
w 30
a. COBB 10/26
20.

10
0

-10 0 10 20 30 40 50 60 70
DAYS AFTER MATURITY


Figure 3. Continued


11








BREWTON,ALA ---" "
QUINCY
GAINESVILLE --- --
9.00 AVON PARK -

8.00 -
-j
S7.00 \

6.00

5.00- --- N






2.00 -

1.00-

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

MONTHS
Figure 4. Monthly average rainfall in inches, based on the 40-year period 1935-1974.







From the data of Butson and Prine (3), the percent chance of re-
ceiving rainfall by weeks for the 40-year period, 1926-1965, was cal-
culated. This was done for two of the same locations, Quincy and
Gainesville. The results were plotted for four different amounts of
rainfall for the soybean growing season (Figure 5). The data for Brew-
ton, Alabama, and Avon Park were not plotted. There was zero chance
of receiving no rainfall for Quincy and Gainesville. The zero chance
of no rainfall at Avon Park lasted the greatest number of weeks. There
was however, a small chance, 5-10 percent, of receiving 0.01-0.49
inches of rainfall for the months of June, July, and first half of August
at Brewton, Alabama. In contrast, the chances of receiving no rain-
fall for the weeks of October 4, 11, 18, and 25 were very great at all
locations.
Thus, seed matured and harvested during the latter part of October
and early November is likely to escape rainfall.
EVALUATION OF SEED FROM COMMERCIAL SEED PRODUCERS
A survey to determine the quality of seed produced by Florida seeds-
men was made in 1974 and 1975. Seedsmen in west and central Florida
were visited and samples of seed secured. Determinations were made
for fungus infection and viability.
Evaluating seed produced by commercial growers proved to be un-
satisfactory from the standpoint of determining whether the seed was
of good or poor quality. Frequently, the seedsman did not know the
maturity date, the harvest date, the length of time between dates of
maturity and harvest, or whether rains fell in the interim. Also, even
though the moisture content of the seed was determined at time of
harvest, the moisture content during storage was unknown. These fac-
tors are all essential for the production of good quality seed and for its
evaluation.
The seed produced in 1974 was generally of poor quality (Tables 4
and 5). The reason for improved quality of seed from western Florida
in 1975 (Table 4) is unclear. One possibility is that following the pub-
lication of the preliminary report on seed deterioration in the Sun-
shine State Agricultural Research Report for September and October,
by Alexander and Hinson (1), and the continued emphasis by the Ex-
tension Staff, growers are paying more attention to prerequisites for
good seed.

DISCUSSION
Soybeans are grown in Florida for processing and for seed. To obtain
the highest grade and thereby greatest income from processing soy-
beans, it is probably sufficient to produce healthy appearing plump
grain. The effect of applying sprays on soybeans will be dealt with in

13















TABLE 4-PERCENT MOISTURE CONTENT, GERMINATION AND CULTURED HEALTHY SEED FROM WESTERN FLORIDA, 1974 AND 1975.
Cultivar and Maturity Harvest Moisture Percent germination Healthy
seed source date date percent Total Healthy (culture
percent)
Santa Rosa County (1974)
Forrest, Jay 9/27 9.92 44.7 42.7 24.0
Forrest, Alabama 10.5 76.3 75.3 36.7
Ransom, Carolina 10.0 66.0 62.7 35.3
Davis, Cert. Ala. 9.8 56.7 52.7 37.3
"Bragg, Jay 10/10 9.6 60.0 48.0 32.0
Hutton, Jay 10/25 9.5 44.0 34.3 36.7
Santa Rosa County (1975)
Forrest, Jay 9/30 11.5 86.0 68.0 -
Davis, Arkansas 11.1 97.0 87.0 -
Bragg, Jay 10/15 11.4 99.0 80.0 -
Bragg, Jay 10/3 10.5 94.0 82.0 -
Centennial, Jay 10/10 11.8 98.0 88.0 -
Hutton, Jay 9.7 98.0 86.0 -
Cobb, Jay 11/10 11.5 89.0 65.0 -












50


40 Quincy, FL /



,- \/ / .

2o" V.,N.... *,, "'..*C -
20- .'- __ \ '. .. -



0
\ a- ..... ....






.C 7 14 21 28 5 12 19 26 2 9 16 23 30 6 13 20 27 4 II 18 25 1 8 15 22 29 6
"" JUNE JULY AUG. SEPT. OCT. NOV. DEC.
4-

0 RAINFALL
SNONE 0.50-0,99in.
12.70- 25.15 mm.
X-. 0.01-0.49in. - 1.0-1.44in. .........
S0.25-12.45mm. 25.4 -50.55 mm.

4)
4,50"
a-
I \ \
40 Gainesville, FL I

A.
30"**"' '"/



S --~ *". i..



0-



7 14 21 28 5 12 19 26 2 9 16 23 30 6 13 20 27 4 1 18 25 '1 15 22 29 6
JUNE JULY AUG. SEPT. OCT. NOV. DEC.



Figure 5. Average percent chance of receiving specific amounts of
rainfall by weeks during the soybean growing season, June 7 to December 6,
at two locations, based on the 40-year period 1926-1965.

15







TABLE 5. -PERCENT MOISTURE CONTENT, GERMINATION, AND CULTURED HEALTHY
SOYBEAN SEED FROM THREE SEED PRODUCERS IN NORTHERN AND
CENTRAL FLORIDA.
Seed produced 1974.
Cultivarand Harvest Percent Percent germination Healthy
seed source date moisture Total Healthy (cultured
percent)
Grower 1
Coker 10.7 27.3 18.7 21.7
Bragg 10.6 60.0 50.0 43.3
Hutton 10.7 74.0 58.7 70.0
Cobb 10.8 88.7 84.0 18.3
Grower 2
Bragg
(1973 seed) 10/29 10.1 90.7 90.0 77.3
Hutton
Foundation 10/21 13.4 64.0 56.0 67.5
Hutton
Foundation 10/22 11.4 85.0 82.0 82.5
Hutton
Certified 10/29 10.6 88.7 87.7 55.0
Cobb
Foundation 10/31 11.8 92.0 89.0 80.0
Cobb
Certified 10/31 9.3 84.7 80.7 80.0
Grower 3
Hardee 12.0 73.0 66.0 64.0
Hardee, bagged 8.5 72.0 68.0 55.0
Hutton 10.8 89.0 87.0 87.5
Cobb, bagged 8.6 83.0 81.0 82.5


a later paper. However, it is demonstrated in this work that harvest
immediately following maturity has a marked influence on the quality
of the grain. Thus, the producers of soybeans for grain should harvest
as soon as seed is mature to secure a high grade and by doing so increase
their income.
Three questions frequently arise concerning the production of dis-
ease-free soybean seed with high viability. 1. Will the extra costs of
production of disease-free seed return sufficient additional dollars to
soybean growers, seed producers, and seedsmen to make it worth
while? 2. What conditions must be met in order to produce disease-
free high viable seed? 3. Can good seed be produced in Florida? The
data presented in this publication shed light on the latter two ques-
tions.
The answer to question 1, regarding the economics of production
and sale of disease-free seed, still must be determined from a com-
mercial standpoint. However, if the economy of using disease-free soy-


16








bean seed can be compared to the economy of using disease-free green
bean seed, disease-free sweet corn seed, and disease-free cabbage seed,
just to mention a few crops, the answer must be yes.
Data are presented which pertain directly to question 2. The data
in Figures 1 and 2 clearly point to the fact that soybean seed harvested
as soon as mature had much less fungal infection and that germina-
tion was high. In order to have the greatest chance of harvesting seed
between maturity and harvest without rainfall, seed should mature
in late October and early November (Figures 4 and 5). In order to ac-
complish this, normal planting dates may need to be changed, espe-
cially with regard to early cultivars and, in many cases, to mid-season
cultivars. The data clearly show that soybeans harvested without rain-
fall, after maturity, are of high quality. Because soybeans planted at
later than the normal planting date tend to yield less, some cultivars,
especially the early-maturing ones, should be planted more thickly.
Generally speaking, thicker planting, in part, compensates for later
planting.
The question, "Can good seed be produced in Florida?", should be
answered in a problematic way; that is, will seed producers use the
necessary measures needed to produce good seed? Surely, good seed
can be produced if growers and seedsmen follow all necessary requi-
sites. Harvest immediately after maturity is a must. Data from other
workers (4, 5,6, 9) show that maintaining a low moisture content dur-
ing storage is necessary. Preliminary information not reported here
indicates that seed properly harvested, dried, and stored at Gaines-
ville germinates excellently and is relatively free of fungal infection.
In order to reduce combine damage, seed may be harvested that con-
tains considerably more than 12 percent moisture. If this occurs, it is
necessary to immediately artificially dry the beans.
These findings substantiate the preliminary report by Alexander
and Hinson (1), 1973, and are in agreement with those published by
Wilcox et al. (30). Ellis et al. (11) published results which show that
soybean seed from southern states has a greater degree of infection
than northern grown seed. The data presented here do not substan-
tiate those of Ellis et al., in part because the degree of seed infections
can vary greatly from year to year depending on rainfall in the differ-
ent areas. Also,to evaluate quality of soybean seed with any degree of
reliability, the seed must be harvested immediately after maturity. If
this is not done, it is difficult, if not impossible, to compare seed quality
from one area with that from another area.
It has been demonstrated by several workers that some internal seed
infection occurs: Crane and Crittenden (7), Ilyas et al. (12), Kilpatrick
(13), Kilpatrick and Hartwig (14, 15), Lehman (20), Lehman and Wolf
(21), Nicholson and Sinclair (24), Wallen and Seaman (28), and Wilcox

17







and Abney (29). Seed infection by Cercospora kikuchii is probably not
influenced greatly by delayed harvest, because it has been shown that
infection occurs during the bloom period: Crane and Crittenden (7)
and Laviolette and Athow (17). If this is the case, properly timed
sprays should reduce infection by this fungus. Spray data obtained at
Gainesville, Florida, by the authors (data to be presented in a separate
paper) indicate that, to some extent, this does happen.
Two additional problems appear to confront seed growers. These are
seed drying and storage. From the observations made on growers' seed,
it would appear that growers are drying their seed at harvest to ap-
proximately 12 percent moisture, a critical point for soybean seed stor-
age. Thus, to be safe, it would appear that when seed is stored, it should
be 10 percent moisture or less. The work of Christensen and associates
supports this viewpoint.
It may be that individual seed growers are not equipped to maintain
dry seed storage; thus, perhaps this should be done by seedsmen who
are equipped to store soybean seed as well as other seed.
If the soybean seed producers of Florida take the necessary precau-
tions to produce good seed, the quality of Florida-grown seed should
equal, or exceed, the quality of seed produced in other southeastern
states.
Environmental conditions some years may cause the production of
poor quality seed, but unfavorable environmental conditions can be at
least partly offset, by having the seed mature during the period, late
October and early November, when the percentage chance of rainfall
is least (Figure 5). Further, because of this favorable period for seed
maturity and harvest, Florida-produced seed usually could very well
exceed the quality of seed produced in other southeastern states.

SUMMARY
A study involving fungal seed infection and germination of soybeans
as affected by delayed harvest and effect of rainfall on seed quality was
conducted, using material from the State Variety Trials at Gainesville,
Florida, for the years 1972-1975, inclusive. In addition, rainfall pat-
terns for Florida were studied and the probability of receiving low
rainfall during specific weeks of harvest was calculated.
It was found that unharvested seed deteriorated rapidly after reach-
ing maturity. Only deterioration caused by fungal infection was stud-
ied. Fungal infection resulted in lowered seed germination.
Rains occurring after maturity caused an accelerated rate of fungal
infection and reduced viability.
Early maturing cultivars do not appear to be more susceptible to
fungal seed infection than late maturing cultivars. However, under
average cultural conditions, early maturing cultivars usually mature


18







during periods of greater rainfall, and unless harvested immediately
after maturity, they tend to be heavily infected with fungi and have
poor viability. Intermediate and late maturing cultivars, especially
the latter, generally mature during periods of infrequent rainfall, and
usually are harvested with less interval between maturity and har-
vest; thus they tend to be of higher quality.
Using the purple stain fungus Cercospora kikuchii as a model, stud-
ies of seed infection by fungi indicate that the degree of seed infection
can be accurately determined only by pure culture technique. In the
case of purple stain, at one harvest approximately 15 times the obser-
vational infection was found by pure culture technique.
The period of least rainfall was found to occur during the last two
weeks of October and the first three weeks of November. For highest
quality seed, soybean maturity should be scheduled for these dryer
weeks and harvest should be accomplished immediately after maturity.
The published work of other investigators has shown that soybean
seed must be stored with moisture content at less than 12 percent.
The research findings presented in this paper indicate that high
quality soybean seed can be produced in Florida if seed producers use
proper growing and harvesting techniques.


























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LITERATURE CITED
1. Alexander, Leonard J., and Kuell Hinson. 1973. Time of harvest is related
to fungal seed infection and germination of Florida grown soybeans. Sun-
shine State Agricultural Research Report, September-October 1973:pp.
12-13.
2. Athow, Kirk L., and Ralph Caldwell. 1954. A comparative study of Dia-
porthe stem canker and pod and stem blight of soybean. Phytopathology
44:319-325.
3. Butson, K. D., and G. M. Prine. 1968. Weekly rainfall frequencies in Flor-
ida. Fla. Ag. Exp. Sta., Inst of Food and Agr. Sci., Circ. S-187, 1-41.
4. Christensen, C. M. 1973. Loss of viability in storage: Microflora. Seed Sci.
and Technol.1:547-562.
5. Christensen, C. M., and C. E. Dorworth. 1966. Influence of moisture con-
tent, temperature, and time of invasion of soybeans by storage fungi. Phy-
topathology 56:412-418.
6. Christensen, C. M., and H. H. Kaufmann. 1972. Biological processes in
stored soybeans. Soybeans: Chemistry and Technology. Chapter 8:278-
293. The AVI. Publishing Co. Inc., Westport, Conn.
7. Crane, J. L., and H. W Crittenden. 1966. The relation of soybean seed
infection by Cercospora kikuchii to the duration of certain plant devel-
opmental stages. Plant Dis. Reptr. 50:464-468.
8. Crittenden, H. W, H. E. Bloss, and E Y. Yelen. 1967. Pod and stem blight
of the soybean in Delaware. Del. Agr. Exp. Sta. Circ. 4, 5pp.
9. Dorworth, C. E., and C. M. Christensen. 1968. Influence of moisture con-
tent, temperature, and storage time upon changes in fungus flora, ger-
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1459.
10. Dunleavy, John. 1969. Consequences of intensive cultural practices on
soybean diseases in the corn belt. Iowa State Univ. Ext. Spec. Rept. 64:35-40.
11. Ellis, M. A., M. B. Ilyas, and J. B. Sinclair. 1974. Effect of cultivar and
growing region on internally seedborne fungi and Aspergillus melleus
pathogenicity in soybean. Plant Dis. Reptr. 58:332-334.
12. Ilyas, M. B., O. D. Dhingra, M. A. Ellis, and J. B. Sinclair. 1975. Location
ofmycelium ofDiaporthe phaseolorum var. sojae and Cercospora kikuchii
in infected soybean seeds. Plant Dis. Reptr. 59:17-19.
13. Kilpatrick, R. A. 1957. RFngi associated with the flowers, pods, and seeds
of soybeans. Phytopathology 47:131-135.
14. Kilpatrick, R. A., and E. E. Hartwig. 1955. Fungus infection of soybean
seed as influenced by stink bug injury. Plant Dis. Reptr. 39:177-180.
15. Kilpatrick, R. A., and E. E. Hartwig. 1955. Effect of planting date on in-
cidence of fungus infection of Ogden soybean seeds grown at Walnut Hill,
Florida. Plant Dis. Reptr. 39:174-176.
16. Kmetz, Konrad, A. E Schmitthenner and C. W. Ellett. 1973. Systemic in-
fection of soybean by seed-rotting Diaporthe and Phomopsis spp. Second
Int. Cong. Plant Path. Minneapolis, Minn. Abstr. No. 0449.
17. Laviolette, F A., and K. L. Athow. 1972. Cercospora kikuchii infection of
soybean as affected by stage of plant development. Phytopathology Abstr.
62:771.


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18. Lehman, Samuel G. 1923. Pod and stem blight of soybean. Ann. Missouri
Bot. Garden 10:111-179.
19. Lehman, Samuel G. 1928. Frog-eye leaf spot of soybean caused by Cer-
cospora diazu Miura. J. Agr. Res. 36:811-833.
20. Lehman, Samuel G. 1934. Frog-eye, Cercospora diazu Miura, on stems,
pods, seeds of soybean and the relation of these infections to recurrence
of the disease. J. Agr. Res. 48:131-147.
21. Lehman, S. G., and Frederick A. Wolf. 1926. Soybean anthracnose. J. Agr.
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22. Milner, M., and W. Geddes. 1945. Grain storage studies II. The effect of
aeration, temperature and time on the respiration of soybeans containing
excessive moisture. Cereal Chem. 22:484-501.
23. Milner, M., and W. Geddes. 1946. Grain storage studies III. The relation
between moisture content, mold growth, and respiration of soybeans. Ce-
real Chem. 23:225-247.
24. Nicholson, J. E, and J. B. Sinclair. 1973. Effect of planting date, storage
conditions and seedborne fungi on soybean seed quality. Plant Dis. Reptr.
57:770-774.
25. Ramstad, P. E., and W. E Geddes. 1943. The respiration and storage be-
havior of soybeans. Minn. Agr. Exp. Sta. Tech. Bull. 156:23-42.
26. Tiffany, Lois H. 1951. Delayed sporulation of Colletotrichum on soybean.
Phytopathology 41:975-985.
27. Wallen, V R. 1960. A high incidence ofDiaporthe phaseolorum occurring
in the seed of soybeans from Southwestern Ontario. Plant Dis. Reptr.
44:596.
28. Wallen, V R., and W. L. Seaman. 1963. Seed infection of soybean by Dia-
porthe phaseolorum and its influence on host development. Can. J. Bot
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29. Wilcox, J. R., and T. S. Abney. 1973. Effects of Cercospora kikuchii on
soybeans. Phytopathology 63:796-797.
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58:130-133.
31. Wolf, Frederick A., and S. G. Lehman. 1926. Brown-spot disease of soy-
bean. J. Agr. Res. 33:365-374.
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