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Group Title: Circular - University of Florida Institute of Food and Agricultural Sciences ; 394
Title: Rootstocks for citrus in Florida
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067215/00001
 Material Information
Title: Rootstocks for citrus in Florida
Series Title: Circular
Physical Description: 13 p. : ill. ; 23cm.
Language: English
Creator: Lawrence, Fred P
Bridges, Don
Publisher: University of Florida.
Institute of Food and Agricultural Sciences.
Florida Cooperative Extension Service
Place of Publication: Gainesville Fla
Publication Date: 1973 ?
 Subjects
Subject: Citrus -- Rootstocks   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Fred P. Lawrence and Don Bridges.
General Note: Cover title.
General Note: Includes summary of rootstock information as of 6/30/73.
Funding: Circular (Florida Cooperative Extension Service) ;
 Record Information
Bibliographic ID: UF00067215
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 20032835

Table of Contents
    Historic note
        Historic note
    Front Cover
        Front cover
    Main
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





Circular 394


Rootstocks for Citrus in Florida

By
Fred P. Lawrence and Don Bridges


Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville










Rootstocks for Citrus in Florida
By Fred P. Lawrence' and G. Don Bridges'

Foreword-This circular is not intended as a comprehensive
treatise on rootstocks. Rather, its threefold purpose is (1) to
provide a reference to the selective effects of important diseases
with various rootstock-scion combinations; (2) to indicate risk
areas where current knowledge and experience are limited; and
(3) to provide a basis for helping the grower answer the im-
portant and rather confusing question What Rootstock shall
I use?

Introduction

Seeds of sour and sweet oranges, lemons and limes were
introduced by the Spanish more than 400 years ago. These im-
ports strongly influenced the present pattern of rootstocks in
Florida's citrus groves. At the time Florida was acquired by
the United States, two and one-half centuries after citrus was
introduced, wild citrus trees flourished in many locations over
most of the peninsula. These wild citrus trees occurred most
frequently in rich hammocks bordering lakes and rivers, and
around sites of old Indian villages. Several wild groves contained
thousands of bearing trees and spread over large areas. Sour
and sweet oranges predominated in the north, but rough lemon
and limes grew also around Lake Okeechobee and lower coastal
areas.
Budded citrus became common in Florida after 1870; prior
to that time both commercial and home plantings consisted
mostly of sweet orange seedlings. As budding was more gen-
erally practiced, sweet orange seedlings were often used as the
rootstock, but these later lost favor because of the prevalence of
root rotting problems. On the other hand, sour orange and rough
lemon became Florida's basic rootstocks, and together presently
constitute the rootstock for about 80% of Florida's citrus trees.
The full impact of the early introductions on our present day
industry is even better appreciated by checking the list of scion
varieties selected from early Florida-grown sweet orange seed-


SProfessor, (Extension Citriculturist), Department of Fruit Crops
2Chief, Citrus Budwood Registration Bureau, Florida Department of Agriculture
and Consumer Services








lings; a list which includes such cultivars as: 'Hamlin', 'Parson
Brown', 'Pineapple', 'Enterprise', 'Homosassa', and 'Queen'.


Rootstock Effects

Rootstocks exert a vital influence on the production of citrus
and their importance must not be ignored when planting or
buying a grove. The wrong rootstock for a given soil type or
scion variety can mean the difference between success and
failure of a grove operation. Although any citrus variety can be
used as a rootstock, some are better suited to specific conditions
than are others. Among other things, rootstocks influence tree
vigor, cold hardiness, fruitfulness, fruit quality, fruit size, and
insect and disease tolerance or resistance. In Florida, citrus is
successfully grown on a wide range of soil conditions and the
different rootstocks vary considerably in their reaction to in-
dividual situations. Any grower is well advised to secure the
counsel of citrus specialists or a qualified soil scientist concern-
ing land preparation and rootstocks, especially where flooding,
waterlogging or high water tables can occur. Information deal-
ing with soil adaptation and effect of rootstocks on fruit
quality are found in the Summary Table under "Characteristics"
and "Special Requirements".
As stated, most of the 72 million citrus trees in Florida
groves are propagated on rough lemon or sour orange rootstocks.
Many useful facts have been accumulated, mostly by grower ex-
perience, about the performance of these rootstocks with various
scion combinations and under a wide range of soil and climatic
conditions. Unfortunately, many important questions remain to
be answered concerning rootstocks less thoroughly tested.

The Role of Rootstock Research

In the past, the main criteria for selecting rootstocks have
been tree size and vigor with large, vigorous trees preferred.
Presently, with higher costs of both land and labor, growers are
using closer tree spacings to increase early yields, and expect
to maintain small compact trees by topping and hedging. Re-
search has demonstrated that greater per acre yields can be
secured during the early years with increased tree density, and
with proper pruning, consistent good yields can be maintained
throughout the life of the tree. Hedging, however, is not the









ultimate solution as it adds to production costs and removes
valuable fruiting wood. Thus, a constantly changing industry
dictates a need for new and better stocks. In Florida, the unan-
swered questions confronting the rootstock research worker are
numerous. It is unrealistic to expect to find a single rootstock re-
sistant to all diseases, nematodes, cold weather, poorly-drained
soils, deep sands, droughts, and which also consistently produces
abundant crops of high quality fruit with all scion combinations
on compact trees. More than 50 scion types that vary widely in
their reactions to diseases and rootstocks are commercially pro-
duced. Ideally, each cultivar should be fitted to a particular stock
to perform best under specific but varying conditions of environ-
ment and purpose (processing, fresh fruit, ornamental, etc.).
With literally hundreds of potentially useful rootstocks from
which to choose and with a wide variety of soils and other en-
vironmental factors, it becomes a practical impossibility for re-
search to provide all answers. Research efforts must therefore
be directed to specific limited goals. Much rootstock information
will necessarily have to come from grower trial-and-error type
experience. Nevertheless, current knowledge regarding the attri-
butes and limitations of rootstocks is extensive. The next section
of this circular and the rootstock table, which indicates prob-
lem areas, should be studied carefully by every citrus grower
in order to avoid costly mistakes.

Reaction of Rootstocks to Diseases, Nematodes,
and Cold
Tristeza: Tristeza is a virus disease transmitted by certain
aphids and by vegetative propagation. It affects all citrus types
(except lemons) propagated on sour orange and other sus-
ceptible stocks. The virus is present in millions of citrus trees
throughout Florida, including many on sour orange rootstock;
however, visible damage is sporadic suggesting that a mild strain
of the virus is prevalent. Recent loss of trees growing on sour
orange rootstock in Hillsborough, Pasco, Polk, Lake, Orange, and
St. Lucie counties, however, convincingly demonstrates the dam-
aging potential of this disease. Current popular use of sour
orange as a rootstock for sweet oranges and mandarins is con-
sidered poor judgment by most research personnel. The risk is
apparently less when grapefruit varieties are used as scions.
A survey of tristeza-infected trees by the Division of Plant
Industry in 1972 disclosed a massive spread of the virus in
commercial groves located in Hardee, Highlands, Martin, Indian









River, and St. Lucie counties. A major portion of this virus
movement appears to have taken place recently, hence the ulti-
mate effect cannot be accurately judged at present. It may be
significant, however, that sizable tristeza tree losses are now
apparent in one of these areas. The adverse effects of tristeza
can be avoided by using tolerant stocks (Table 1).
Exocortis: This virus disease is prevalent in Florida, in-
fecting most old-line trees. No insect vector is known, exocortis
being transmitted by budding and mechanically by tools used for
propagation and pruning. A 10% solution of household bleach
(Clorox) is an effective sterilant for tools. Various strains of
virus differ widely in their effect on susceptible trees, but viru-
lent strains generally produce severe stunting and loss of yield.
Trees on trifoliate orange (Poncirus trifoliata) and most of its
hybrids are severely affected. Trees on sweet lime and Rangpur
lime rootstocks are also susceptible to exocortis. Exocortis dam-
age can be avoided by using tested exocortis-free bud-source
trees and proper sterilization of tools.
Xyloporosis: This bud-transmitted virus is widely distrib-
uted in Florida's older commercial trees, mostly in symptomless
form as many combinations of scions and rootstocks tolerate
the virus. This disease, however, is detrimental to trees on
C. macrophylla, Rangpur lime and 'Palestine' sweet lime. Xylo-
porosis-free trees are plentiful and are commonly produced by
reputable nurseries. Growers, however, must be extremely care-
ful when top-working symptomless but probably infected grove
trees as several scion varieties are also severely affected by
xyloporosis, regardless of rootstock. These include 'Orlando' and
'Minneola' tangelos, 'Murcott', satsuma, 'Robinson', 'Osceola',
'Lee', and probably 'Page' and 'Nova' also, as they are hybrids
of susceptible parents. Xyloporosis-infected trees should not be
topworked to the above cultivars or vice-versa. Xyloporosis-
infected trees are often stunted with flattened, unthrifty tops,
fruits are small and yields poor.
Psorosis: Psorosis is a virus which adversely affects all
commercial citrus cultivars, regardless of rootstock. Psorosis is
transmitted almost solely by budding or grafting infected bud-
wood. However, a small percentage of seed from infected 'Car-
rizo' citrange carry the virus. Damaging symptoms occur al-
most solely on mature trees, which often have distorted limbs
and areas of scaly bark which enlarge until limbs or trunks are
girdled. Psorosis, which was common 20 or more years ago,









can be avoided by purchasing trees registered free of this virus.
Florida law now prohibits the sale of psorosis infected nursery
stock.
Foot Rot: This is a fungus disease caused by one or more
species of Phytophthora which, with its associated root rots, has
probably killed more trees in the past than any other citrus
disease, except perhaps blight. Special cultural practices should
be followed in the seedbed, nursery, and grove to reduce this
disease. Hot water treatment of seed, budding further above
ground level, and soil fumigation contribute to successful use of
the stocks known to be susceptible to the disease.
Young Tree Decline: This condition was first recognized
in 1964 and was originally thought to be a problem related to
poorly-drained soils. Currently, it is being reported from other
areas, including the well-drained "Ridge" soils. Although clas-
sified as a disease, the casual agent for "Young Tree Decline"
is not known. This disease is not readily distinguished from citrus
blight, which was observed as far back as 1895 and for which
a casual agent is still not known. YTD has been reported affect-
ing trees on several rootstocks, and none may be immune; how-
ever, it is undoubtedly more common on rough lemon. Based
on limited observation, it is as common on 'Estes' as on reg-
ular rough lemon. The widespread damage of YTD to trees
propagated on rough lemon stock has resulted in the virtual dis-
continuance of use of this stock for new plantings.
Stem Pitting: This non-specific term refers to a conditoin
discovered by Florida Department of Agriculture & Consumer
Services personnel in mid-1972. Field surveys produced rather
convincing evidence that an insect vector is involved and is
widely distributed in citrus producing counties. While rather
comprehensive cooperative investigations are under way, more
time is needed to develop full information. Presently, there is
sufficient experimental evidence to establish that the pitting
observed is NOT associated with tristeza virus infection.
Stem pitting symptoms ranging from slight to severe have
been found on more than 20 commercial citrus cultivars with
'Robinson', 'Page', sweet lime, and 'Milam' displaying the most
severe manifestations yet discovered. All pitted trees discovered
to date appear healthy and vigorous and any possible future
effect cannot be predicted.
Burrowing Nematode (Radopholus similis (Cobb) Thorne):
See Circular S-151 and Table 1.









Citrus nematode (Tylenchulus semipenetrans): This wide-
spread nematode is responsible for important losses in tree vigor
and fruit production. Mature infested trees decline with symp-
toms that are similar to but generally less obvious than those of
spreading decline affected trees. Most citrus rootstocks are
susceptible. Moreover, the burrowing nematode-tolerant root-
stocks now available are not tolerant of the citrus nematode.
Research indicates that it is possible to increase tree vigor and
yield when citrus nematode infested trees are chemically treated
in place.
Freeze Damage: Trees budded to trifoliate orange, sour
orange, sweet orange, and 'Cleopatra' mandarin rootstock are
relatively cold hardy. Citrus trees on 'Carrizo' citrange seed-
lings, rough lemon, 'Milam', Rangpur lime, and sweet lime are
less tolerant to cold. Dormancy is a key factor in cold hardiness.
In warm locations where young trees grow into the winter,
they may suffer freeze damage on any rootstock. Under these
circumstances, special cultural practices such as withholding fer-
tilizer and water late in the season to encourage dormancy may
be helpful. Trees with virus infection, notably psorosis, are much
more susceptible to freeze damage.

Validated Seed Sources
Research has demonstrated that even within a single horti-
cultural variety individual trees can and do differ widely in their
reactions to disease organisms, nematodes, and quite possibly
other important characters.
This information has stimulated owners of established
nurseries to plant only seeds from validated sources that are
known to be from selections that are virus free, true-to-type,
and often with other desirable tested qualities. It is hoped that
these plantings will ultimately lead to registered seed source
trees (free of viruses, true to variety and with other proven
characters) which completely replace the untested source trees
used earlier.
It is recommended that growers be alert to take advantage
of the superior trees that are available on tested stocks. The
person who "shops" or "bargains" for "cheap" trees, and pays
no attention to the seed and bud source can be making a very
costly error in judgment. It should be obvious that trees pro-
duced on rootstocks from validated seeds and registered bud-
wood are a very good investment.










Summary
In several respects the present rootstock picture is frustrat-
ing, especially to growers who can't afford to sit and wait for
all the answers. It should be clear, however, that in the future
we can't afford the luxury of broad generalizations or hit-or-
miss methods. Instead, every citrus man must make a concerted
effort to fit the rootstock to a specific scion variety, the planting
layout of his grove, the predominant soil type, climatic and
disease environments, and carefully choose the seed and bud-
wood source which will produce the variety and quality of fruit
needed for a specific market.
Growers contemplating sizable plantings should give serious
consideration to the use of more than one rootstock until some
of the present questions are resolved.
Hopefully, the summary of rootstock information that
follows will enable one to make a wiser decision at this time.

ACKNOWLEDGMENTS
We are deeply grateful to those of the University of Florida's
Agricultural Research and Education Center at Lake Alfred, and the
USDA Horticultural Field Station at Orlando, whose research findings
were of great value in the preparation of this circular. We especially
thank Dr. S. M. Garnsey, Dr. A. H. Krezdorn and Dr. H. J. Reitz for
reviewing and editing the several preliminary drafts and helping us with
this publication.










TABLE 1.
SUMMARY OF ROOTSTOCK INFORMATION AS OF 6/30/73
Specific clones within a variety may vary widely in their reactions to nematodes and disease organisms. Horticultural factors also
differ. Where special characteristics are known, specific information is noted. (Example: The burrowing nematode resistance of 'Ridge
Pineapple' sweet orange.)


Performs well on a wide range of soils,
especially deep sands. Produces large
trees and fruits. Yields are excellent.
Lowers fruit quality.


'Estes' Lemon Appears similar to rough lemon based
(C. jamhiri var.) on limited trials. Tolerant to burrowing
nematode (Radopholus sinilis).









'Milam' Appears generally similar to rough
(possible hybrid lemon based on limited trials, EXCEPT:
C. jamhiri Lush.) has resistance to burrowing nematode,
better fruit quality. Is severely pitted by
the "new" stem pitting disease. Pitted
trees appear otherwise normal at
present.


Rootstock Variety Characteristics


Major Risk Factors

It is currently the
rootstock most wide-
ly affected by Y.T.D.
.and freeze damage.


Limited grower ex-
perience.
Apparently suscep-
tible to Y.T.D. and
freeze damage.


Special Requirements

Warm location.
Scions with high quality
characters.
Precautions against foot
rot.
Timely removal of root-
sprouts. Adequate room to
grow.

Apparently the same as
rough lemon.










Apparently the same as
rough lemon, except a pos-
sible wider selection of
scion varieties.


Indicated Usefulness

Questionable u n t i
more is known
.about Y.T.D. and/or
S.H.D.


Questionable u n t i
more is known about
Y.T.D. and S.H.D.
Restrict to warm lo-
cations near bur-
rowing nematode in-
festations. With 'Va-
lencia', 'Pineapple',
'Queen', 'Marsh', or
'D a n c y' tangerine
scions.

Other than 'Ridge
Pineapple' and 'Car-
rizo 'Milam' is the
only rootstock rec-
ommended for use
in or adjacent to the
w a r m e r locations
pushed and treated
for spreading de-
cline.


Limited grower ex-
perience.
Reaction to Y.T.D.
not established.
Freeze damage. The
ultimate effect of
stem pitting on
'Milam' rootstock is
not known pres-
ently.


Rough Lemon
(Citrus jambhiri)










Rootstock Variety Characteristics Special Requirements Major Risk Factors Indicated Usefulness

Rangpur Lime Based on limited experimental and cor- Warm locations. Limited grower ex- Worthy of trial use
(C. reticulata mercial use, Rangpur, with virus-free Xyloporosis and exocortis- perience. Reaction to (limited acreage)
Blanco var. budwood, apparently grows well and pro- free budwood. Y.T.D. and "stem under high quality
austera Swing.) duces large vigorous trees on a variety Adequate room to grow. pitting" not estab- round oranges and
of soil types including deep sands. Yields lished. Susceptible to grapefruit in warm
and fruit size are excellent. Fruit quality cold damage and locations, especially
is only fair but better than rough lemon. foot rot. East Coast.
Tristeza tolerance and drought resist-
ance are good.


Based on very limited use, sweet lime
with virus free budwood produces
large, fast growing, superior yielding
trees on deep sand. Fruits are large,
with quality similar to rough lemon. On
young trees fruit may be riceyy" espe-
cially if left on the tree past peak
maturity.


Does well on heavy soil and on sands
with clay sub-soil. Average fruit size is
below rough lemon but quality is good
and fruits hold well on the tree. Young
trees may grow somewhat slower and
produce less than some other stocks but
both differences are less apparent in
mature trees. Has no major disease prob-
lem when a good cultural program is
followed.


Warm locations.
Scions with high quality
characters.
Precautions against foot
rot. Adequate growing
room. Exocortis and xylo-
porosis-free budwood.


Good drainage and precau-
tions against foot rot are
beneficial.


Almost no grower
experience.
Reaction to Y.T.D.
and "'stem pitting"
not established.
Freeze damage.
Reaction to Florida
tristeza strains not
firmly established.
It is not significant-
ly foot rot resistant.


Small fruit sizes in
most locations, espe-
cially with "Valen-
cia' scions. This may
be partially over-
come with proper
cultural methods.


Very high yields in-
dicate this stock is
worthy of limited
trial in warmer lo-
cations with nucel-
lar scions of 'Valen-
cia', 'Marsh' and red
grapefruit, and
'D a n c y' tangerine.
Tangerine sizes are
very good.


"Cleo" is a good
rootstock for hy-
brid varieties and
grapefruit for the
late market. May be
one of our best root-
stocks where tris-
teza and/or Y.T.D.
are threats.


Sweet Lime
(C. limettioides
Tan.)


Cleopatra
Mandarin
(C. reshni Hort.
ex Tan.)











Rootstock Variety Characteristics
Poncirus tri- Does best on heavy soils using exocortis-
foliata (Linn. free budwood. Once dormant it contrib-
(Raf.) utes the most cold hardiness of any root-
stock presently in use. Fruit quality is
excellent and fruits hold well on the tree
except for 'Pineapple'. Almost immune
to foot rot.


Grows well with virus-free budwood on
most citrus soils, except the lightest
sands and calcareous soils. Is tolerant
to burrowing nematodes. Fruit quality
is good and fruit size adequate. Yields
are good based on limited comparative
data.


Special Requirements
Good soil, exocortis free
budwood.
Plentiful supplies of mois-
ture and plant nutrients are
beneficial but special re-
gimes are not critical.
Avoid calcareous soils.


Exocortis-free budwood.


Major Risk Factors Indicated Usefulness


Limited commercial
experience with
most varieties (sat-
suma excepted). Re-
action to Y.T.D. not
established. Will not
tolerate calcareous
soils.


Y.T.D. reaction not
established. The ap-
parent tristeza tol-
erance of 'Carrizo'
could be questioned
on the basis of re-
cent California ex-
perience with 'Troy-
er' and 'Carrizo's'
closeness to that
stock. Somewhat
limited commercial
experience if a 1
scion varieties are
considered. (We 11
over a million of our
commercial g r o v e
trees are on 'Car-
rizo', but most are
rather young.)


At present, trifoli-
ate is considered a
special situation
rootstock. Use with
nucellar scions in
cold locations on
heavy noncalcareous
soils. Worthy of lim-
ited acreage trials
on good soils with
'Minneloa' tangelo,
navel orange and
'Duncan' grapefruit.

The wide range of
soils and scions to
which 'Carri z o'
seems well adapted;
its freedom from di-
sease problems that
cannot be effectively
controlled; and its
advantages for use
around spreading
decline areas all in-
dicate that 'Carrizo'
may become a ma-
jor rootstock unless
problems develop
with Y.T.D. and/or
tristeza.


'Carrizo' Citrange
(C. sinensis x
o P. trifoliata)








Rootstock Variety Characteristics Special Requirements Major Risk Factors Indicated Usefulness
'Rusk' Citrange Produces trees that are noticeably Must use exorcortis- free Limited cultural in- This stock budded
(C. sinensis x P. smaller and rounded in shape when non- budwood. formation under to old-line 'Valen-
trifoliata) virus free scion wood is used. Even so, commercial gro ve cias' may prove very
it produces good crops (for tree size) conditions, desirable for high
of excellent size and quality fruit, density plantings. It
should not be used
extensively u n t i
more information is
available.
'Trover' Citrange Apparently similar to 'Carrizo' except Exocortis-free budwood. Very limited grow- Not presently rec-


it is NOT tolerant to burrowing nema-
tode. Not as widely planted as 'Carrizo',
therefore, experience is very limited.






Produces extremely large, fast growing
trees with virus-free budwood. Fruit
quality is poor. Very tender to cold.
Highly tolerant to phytophthora.





Has a shallow lateral root system. Pro-
duces vigorous growing tree with large
fruit of acceptable quality.


Warm location.
Tristeza and xyloporosis-
free budwood. Tristeza-free
environment except under
lemon scions. Adequate
growing room.


Heavier more fertile soils.


erexperience. Y.T.D.
reaction not estab-
lished. Recent ex-
perience in Califor-
nia indicates 'Troy-
er' is damaged by
tristeza in some
areas but not in
others.


ommended because
of the lack of prac-
tical or experimen-
tal information and
its similarity to
'Carrizo' which has
the advantage of
burrowing nematode
tolerance.


No grower experi- Not recommended
ence. Tristeza. for commercial use
Freeze damage. except limited acre-
Y.T.D. reaction not age trial under xylo-
known. porosis and tristeza-
free lemon scions in
our warmest loca-
tions.
Stocks have not Not presently rec-
been used extensive- ommended, however,
ly in recent years, it may have a place
in flatwoods plant-
ings on the heavier
soils.


(C. sinensis x
P. trifoliata)


Citrus macro-
phylla


'Duncan' grape-
fruit (C. paradise
Macf.)











Rootstock Variety Characteristics Special Requirements Major Risk Factors

Sour orange Produces standard size, cold hardy trees Not well suited to deep in- Tristeza.


(C. aurantium L.)


on our heavier soils. Box yields and
average fruit size are less than rough
lemon but excellent fruit quality is ad-
vantageous for both the fresh fruit and
concentrate markets. Can be used with
a wide range of scion varieties and fruit
holds well on the tree after maturity.


fertile sands. Tristeza-free
budwood.
Tristeza free environment
(see discussions of tristeza
disease).


Indicated Usefulness
Based on field ob-
servations sour is
among the root-
stocks least affected
by Y.T.D. Consid-
er e d satisfactory
only for lemons;
however, based on
experience, the use
of sour under grape-
fruit is less risky
than with oranges,
mandarins, etc. The
recent massive and
widespread build-up
of tristeza infection
in groves and the
increasing loss of
sour root trees in
"hot" tristeza areas
around the state
could forecast a
much more serious
tristeza problem
than Florida-has yet
experienced.


Sweet orange Produces large, fast growing, cold Good drainage and all Foot rot and asso- Based on field ob-
(C. sinensis) hardy trees. Fruit size, quality and known precautions against ciated root rots. servation, it appears
yields are all good but it tends to ac- foot rot. to be among the
centuate alternate cropping. Trees wilt Irrigation. rootstocks least af-
quickly and suffer during dry weather. Adequate room to grow. fected by Y.T.D. Its
Has no major disease problem except inability to with-
susceptibility to phytophthora root rot- stand drought, cou-
ting fungi. Suitable for use with a wide pled with spotty foot
range of scion varieties. (Continued on Pg. 7)








Rootstock Variety Characteristics


Sweet orange
(Con't.)












'Ridge Pineapple'
(C. sinensis)
co


Special Requirements


Same as sweet orange except RESIST-
ANT to burrowing nematodes.


Same as sweet orange
based on limited experience.


Major Risk Factors Indicated Usefulness

rot experience con-
tribute to the gen-
eral unpopularity of
this rootstock with
growers. Presently
not generally recom-
mended; however, if
clones with higher
phytophthora toler-
ance are found,
sweet orange would
be useful where
Y.T.D. and/or tris-
teza are problems.


Same as sweet or-
ange based on limit-
ed experience.


Same as sweet
orange EXCEPT
'Ridge' is the only
rootstock now avail-
able suitable for use
in or adjacent to
COLD areas pushed
and treated for bur-
rowing nematodes.


MISCELLANEOUS STOCKS: In addition to the 15 rootstocks listed, all of which are available or can be made available by Florida
nurseries, there are many hundreds of other selections that appear to have rootstock potential. A surprisingly large number (several
hundred) are now included in experimental rootstock plantings. Others, such as the 'Bittersweet' orange (C. aurantium L.) have been
used commercially on a very minor scale but are rarely, if ever, used today. None are of sufficient importance or stage of research
development to justify discussion here.

















































COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
Joe N. Busby, Dean










4-20M-74

This public document was promulgated at an
annual cost of $972.22, or 5 cents per copy to
inform citrus growers about rootstocks.




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