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
I(L/v
if" &'O
BUNCH GRAPE FIELD DAY
UNIVERSITY OF FLORIDA
INSTITUTE FOR FOOD AND AGRICULTURAL SCIENCES
AGRICULTURAL RESEARCH AND EDUCATION CENTER, LEESBURG
Thursday, July 11, 1985
9:30 2:30
Dr. Mary C. Halbrooks, Fruit Crops Departmenlt-=-Moderator "
9:30 10:20 Registration and bunch grape ul ivar fresh fruit
and juice taste panel. (All p ople attendingg are
invited to rate varieties and reed4iri selectionss
for quality.)
10:25 11:25 A guided tour of the 17 acre r pQh.O -yx--dhridoda
will be conducted. Of special lK est-i-wll-1-b're- .
experimental seedless cultivars, a vineyard
sprayer in operation, an overhead arbor, maxi-jet
irrigation, T-budding as a top working technique
and screenhouses.
11:30 noon Travel to Leesburg Community Building, 109 E.
Dixie Ave.
Noon 12:55
12:55 1:00
1:00 1:20
1:25 2:30
Catered lunch (Fried Chicken $4.00/person).
Dr. G. W. Elmstrom, Center Director; AREC
Leesburg. Welcoming Remarks.
IFAS Centennial multi-image presentation.
Presentations by AREC faculty regarding current
research on grapes at Leesburg.
1:25 Dr. D. L. Hopkins, Plant Pathologist; AREC Leesburg.
Grape Fungicide Tests.
1:35 Dr. W. C. Adlerz, Entomologist; AREC Leesburg. Insect
Control on Florida Bunch Grapes.
1:45 Dr. R. P. Bates, Food Scientist; Department of Food
Science & Human Nutrition.
1:55 Dr. J. A. Mortensen, Geneticist; AREC Leesburg.
Breeding Grapes for Florida.
2:05 Dr. M. C. Halbrooks,.Extension Horticulturist,
Viticulture; Fruit Crops Department. Gibberellin
Applications on Experimental Seedless Bunch Grapes.
2:15 Dr. D. J. Gray, Developmental Biologist; AREC
Leesburg. Use of Tissue Culture for Production of
Grape Varieties Adapted to Florida.
2:25 Conclusion
Refreshments on tour courtesy of Abbott Lab
Leesburg AREC Research Report (LBG 85-1)
300 Copies
The Institute of Food and Agricultural Sciences is an Equal Employment Opportunity Affirmative Action Employer authorized to provide research,
educational information and.other services only to individuals and institutions that function without regard to race, color, sex, or national origin.
-2-
Grape Fungicide Tests (D. L. Hopkins)
In 1984, fungicides were evaluated for the control of grape
diseases on 'Stover' grapevines. Test plots were arranged in
randomized blocks with three vines per plot and three
replications. Treatments were first applied on March 21 and
applied every 2 weeks through the season, except DPX-H6573 and
Bayleton which were applied every 3 weeks. Approximately 150
gallons of spray per acre was applied to the plots. Anthracnose
was rated in April, May, and July and bitter rot was rated at
harvest July 17. Isariopsis leafspot was rated on August 1.
Anthracnose began to develop in the plots in March-April but dry
weather reduced disease development in May (Table 1). Benlate +
Orthocide 50, DPX-H6573, and Baycor + Agridex provided excellent
control of anthracnose. Manzate D + Orthocide 50 was also very
effective. However, XE-779L and Bayleton did not provide
adequate control.
Bitter rot and Isariopsis leafspot were controlled by all
fungicides except Bayleton (Table 2). Yields were slightly lower
in the Bayleton and unsprayed plots due to the bitter rot.
In 1985, we also have a fungicide test in progress. This test
will be observed on the vineyard tour. Preliminary results are
given in Table 3.
Table 1. Control of anthracnose with fungicides, 1984.
2
1 Anthracnose rating
Treatment and rate 4/30 5/25 7/5
Benlate + Orthocide (0.1 lb. + 2.0 lbs.) 1.0 a 0.7 ab 1.1 a
DPX-H6573 (0.25 oz. ai) 1.0 a 0.7 ab 1.2 a
Baycor + Agridex (1.0 lb. + 1.0 pt.) 1.1 a 0.1 a 1.3 ab
DPX-H6573 (0.125 oz. ai) 1.0 a 0.6 ab 1.5 b
Manzate D + Orthocide 1.5 ab 1.3 ab 1.8 c
(2.0 lbs. + 2.0 Ibs.)
XE-779L (0.1 lb.) 2.1 abc 1.3 ab 3.1 d
Bayleton (0.25 lb.) 2.5 bc 1.8 b 3.5 e
Unsprayed 3.1 c 3.2 c 4.1 f
1
Sprays were applied biweekly, except DPX-H6573 and Bayleton
which were applied at 3-week intervals. Rates were in amount of
product per acre except for DPX-H6573 which was amount of active
ingredient per acre.
Anthracnose was rated on a scale of 0-10. Mean separation in
columns by Duncan's New Multiple Range Test, 5% level.
-3-
Table 2. Fungicidal control of grape diseases, 1984.
% bitter Yield Isariopsis
Treatment and rate rot (Ibs./plot) leafspot2
DPX-H6573 (0.125 oz. ai) 2 a3 51.5 a 0.5 a
Baycor + Agridex 4 ab 56.4 a 0.1 a
(1.0 lb. + 1.0 pt.)
XE-779L (0.1 lb.) 4 ab 48.5 a 0.7 a
Manzate D + Orthocide 6 abc 44.5 a 0.3 a
(2.0 lbs. + 2.0 lbs.)
Benlate + Orthocide 7 abc 40.0 a 0.3 a
(1.0 lb. + 2.0 lbs.)
DPX-H6573 (0.25 oz. ai) 9 abc 47.0 a 0.4 a
Bayleton (0.25 lb.) 35 bc 33.2 a 3.4 b
Unsprayed 38 c 30.4 a 4.4 b
1
Sprays were applied biweekly, except DPX-H6573 and Bayleton
which were applied at 3-week intervals. Rates were in amount of
product per acre except for DPX-H6573 which was amount of active
ingredient per acre.
3Isariopsis leafspot was rated on a scale of 0-10.
Mean separation in columns by Duncan's New Multiple Range Test,
5% level.
Table 3. Grape fungicide test, 1985.
Treatment
2
Anthracnose rating
4/26 7/2
(G) DPX-H6573 (0.5 oz. ai) 1.0 1.0 a
(C) RH-3866 + Dithane M-A5 + Triton B-1956 1.0 1.0 a
(2 oz. ai + 3.0 lbs. + 2 oz.)
(F) Benlate + Captan 50 (1.5 lbs. + 3.0 lbs) 1.0 1.0 a
(D) RH-3866 + Triton B-1956 (4 oz. ai + 2 oz.) 1.0 1.0 a
(E) Captan 50W + XE-779L 1.0 1.0 a
(3.0 lbs. + .075 lb. ai)
(A) KWG-0519 (2 oz. ai) 1.2 2.4 b
(B) Bayleton (2 oz. ai) 1.5 3.3 c
(H) Untreated 2.3 3.5 c
Rate product per acre is given unless designated as active
ingredient (ai) per acre. Sprays are applied every 2 weeks.
Anthracnose was rated on a scale of 0-10. Mean separation in
columns by Duncan's New Multiple Range Test, 5% level.
II
-4-
Pierce's Disease of Grapevine. (D. L. Hopkins)
Pierce's disease (PD) is caused by a small, xylem-limited
bacteria. The symptoms include decline of vigor, marginal
necrosis of leaves, and often death of the plant. This disease
limits grape production in Florida. Both European type (Vitis
vinifera) and American type (V. labrusca) bunch grapes succumb to
PD.
Presently, the only effective control for PD is resistance. To
be productive in Florida, grapes must be resistant to PD. Most
varieties of muscadine grape have a high level of resistance, but
some are susceptible. 'Pride', 'Carlos', 'Lucida', and
'Scuppernong' are examples of muscadine varieties that are
susceptible to PD in Florida. Among bunch grapes, only varieties
developed at the AREC, Leesburg have enough resistance to PD to
be productive in Florida. These include 'Stover', 'Lake
Emerald', 'Blue Lake', 'Suwannee', 'Daytona', and 'Conquistador'.
Insect Control on Florida Bunch Grapes. (W. C. Adlerz)
Many insects can be found on bunch grapes in Florida. Some can
be severely damaging and control may be necessary. To keep
spraying to a minimum, growers may wish to become acquainted with
insects having the greatest damage potential, inspect vines
frequently, and spray only when necessary. This is a good
strategy, since preventive spraying will not be necessary in most
cases. Exceptions occur when growers experience annual problems
with grape seed chalcid, or if the grower adopts spraying to
control newly emerged root borer larvae in the fall as part of
the grape root borer control program.
Among the most persistent and damaging insects are the grape flea
beetle, grape leafhopper, and grape root borer.
These are discussed briefly.
Grape Flea Beetle
Grapevines are damaged by adult and by larval grape flea beetles.
Adult beetles are dark bluish-black and about 3/16 inch long.
They are usually the first insects of the growing season to
damage grapevines. Adult beetles feed on primary buds which then
cannot develop into primary canes, so crop yield is reduced.
Grape flea beetles breed in the vineyard, and females lay eggs on
various parts of the vine. Larvae are brown, spotted with black,
and about 1/4 inch long. They feed on the upper surface of
leaves and on developing flowers and buds, reducing yields.
Since both adults and larvae are easily seen vineyards should be
carefully monitored in the early season, paying special attention
first to cane and then to flower buds. Insecticides should be
applied when necessary.
Grape Leafhopper
Grape leafhoppers can be expected to infest vines each year.
Adult and immature insects feed on the undersides of leaves
causing pale feeding spots visible from above and even general
discoloration. Vine growth and sugar content of the grapes may
be reduced and seriously affected vines will be weakened.
Excreta from these insects may collect on the fruit which will
then be spotted and possibly covered with sooty mold.
Grape leafhopper adults are light colored, about 1/8 inch long
and very active. Immatures are very small, often difficult to
see, usually immobile, but can be provoked to activity by
touching.
An application of insecticides made prior to flowering and a
second 2-4 weeks after flowering will result in good leafhopper
control if one elects preventive spraying.
Grape Root Borer
Grape root borer may be the most serious threat to grapes in
Florida, having the potential to kill both bunch and muscadine
vines. Larvae tunnel in the roots, reducing root diameters and
girdling even large roots. Large larvae often make their way
into the crown of the plant. Marked reductions in vine vigor and
yield is cause to suspect root borer activity. Detection is by
exposing part of the root system to inspect for larvae or damaged
roots.
Larvae remain in the soil for about 22 months before coming to
the surface to pupate. In Florida, the adult moths are active
and can be seen in the vineyard in daytime, mainly in October.
Adults are brown, wasplike moths with yellow markings. Females
lay eggs on a variety of plant materials or on the ground. Newly
hatched larvae tunnel through the soil to the roots.
The only available chemical control method is spraying the ground
to kill newly hatched larvae in late September and October. The
chemical barrier keeps the larvae from penetrating to the
grapevine roots. Larval; control with this method has been found
effective in Florida. Use Lorsban according to label directions.
Do not apply less than the 2 quarts of dilute spray per vine
called for on the label. A concentration of 2 pints of Lorsban
4E/100 gallons of finished spray is effective. Since the label
limits application to one per season it would be best to make the
application the second or third week in October.
Root borers have been found in most varieties of grapevines in
Florida, (Table 4).
Other Insects or Damage Commonly Seen
Grape leaf folders, grape leaf skeletonizers, grape leaf miners,
grape phylloxera, grapevine aphids, and anomala beetles are
commonly seen in the vineyards.
All are considered minor pests that may not require control
efforts. Grape leaf folders and skeletonizers may be especially
abundant in the late summer and fall. Skeletonizers (brightly
colored yellow and black striped larvae feeding in groups) should
not be allowed to denude vines, so they should be sprayed if
necessary. If foliage disappears, remaining foliage is smeared
with black frass, and no insects are seen, look for anomala
beetles under vines, or look for insects eating foliage at night.
Table 4. Occurrence of grape root borers on various grapes in
the laboratory research planting and a commercial
vineyard: cast pupal skins at the soil surface.
Pupal skins per vine
Laboratory 1 Commercial2
1979 1980 1981 1980 1981
Liberty (Lake Emerald) 0.2 0.5
Stover (Lake Emerald) 0.4 1.0
Blue Lake 0.4 1.7
Lake Emerald 0.8 0.4
Norris (Lake Emerald) 1.2 1.0
L4-33 (Dogridge) 2.3
Southland 0.0 0.5 0.4 0.6 0.4
Magnolia 0.0 0.2 0.0 0.6 0.5
Thomas 0.2 0.3 0.6
Redgate 0.2 0.8 1.0
Chief 0.2 0.0 0.5 0.3
Regale 0.3 0.0 0.0
Magoon 0.5 0.2 0.3
Tarheel 0.7 0.3 0.6 1.4 0.4
Welder 0.8 0.0 0.6 2.6 0.6
Watergate 0.8 0.0 0.0
Fry 0.8 0.3 0.5 2.6 1.2
Creek 0.8 0.0 0.3
Dixie 1.2 0.3 0.8 0.4 2.2
Dearing 1.2 0.3 0.0
Jumbo 1.3 0.0 1.3 4.0 3.6
US42-12B 2.2 0.2 0.5
Cowart 2.2 0.0 0.6
Noble 2.3 0.3 0.8
Hunt 2.3 0.6 1.4 3.4 1.2
Sugargate 3.3 0.3 2.6
Carlos 3.6 0.2 0.0 2.5 1.7
Higgins 4.0 0.0 0.7 2.7 2.3
2Average from 6 single-plant replications.
Average from 5 to 15 plants of each variety.
-7-
Insecticides for Bunch Grapes
When to spray
Insecticide
Bud break to flowering
(or later for beetle)
Pre-bloom and
2-4 weeks after bloom
Late April through
May, weekly
Post harvest
As needed
For mid September
to early November
control of new larvae
Malathion or
Methoxychlor or
Carbaryl (Sevin)
Methoxychlor or
Carbaryl (Sevin)
Malathion
(as above)
Malathion
Methoxychlor
or
Carbaryl (Sevin)
Lorsban
Flea beetle
Leafhopper
Leafhopper
Seed
Chalcid
Leafhopper
Aphids
Leafhoppers 2
Caterpillars
Fruit beetles
Root borer
Malathion
Carbaryl
Methoxychlor
Lorsban
1.5 pints 57% emulsifiable concentrate/100 gal.
water
1.5 teaspoons/gallon
Days before harvest 3
2 pounds 50% carbaryl wettable powder/100 gal.
water
2 tablespoons/gallon
Days before harvest 0
2 pounds 50% methoxychlor wettable powder/100 gal.
water
2 tablespoons/gallon
Days before harvest 14
Specific recommendation on label
When this insect is a problem preventive spraying will be
needed.
Grape leaf folder, leaf skeletonizer, hornworms, berry moths.
In central Florida the earliest observed flight of root borer
moths has been September 9. and the latest has been November 3.
Peak flight was the first week in October in 3 of 5
observations. Apply Lorsban the second to third week in October
to kill new larvae.
Pest
~
~
~
-4-
Pierce's Disease of Grapevine. (D. L. Hopkins)
Pierce's disease (PD) is caused by a small, xylem-limited
bacteria. The symptoms include decline of vigor, marginal
necrosis of leaves, and often death of the plant. This disease
limits grape production in Florida. Both European type (Vitis
vinifera) and American type (V. labrusca) bunch grapes succumb to
PD.
Presently, the only effective control for PD is resistance. To
be productive in Florida, grapes must be resistant to PD. Most
varieties of muscadine grape have a high level of resistance, but
some are susceptible. 'Pride', 'Carlos', 'Lucida', and
'Scuppernong' are examples of muscadine varieties that are
susceptible to PD in Florida. Among bunch grapes, only varieties
developed at the AREC, Leesburg have enough resistance to PD to
be productive in Florida. These include 'Stover', 'Lake
Emerald', 'Blue Lake', 'Suwannee', 'Daytona', and 'Conquistador'.
Insect Control on Florida Bunch Grapes. (W. C. Adlerz)
Many insects can be found on bunch grapes in Florida. Some can
be severely damaging and control may be necessary. To keep
spraying to a minimum, growers may wish to become acquainted with
insects having the greatest damage potential, inspect vines
frequently, and spray only when necessary. This is a good
strategy, since preventive spraying will not be necessary in most
cases. Exceptions occur when growers experience annual problems
with grape seed chalcid, or if the grower adopts spraying to
control newly emerged root borer larvae in the fall as part of
the grape root borer control program.
Among the most persistent and damaging insects are the grape flea
beetle, grape leafhopper, and grape root borer.
These are discussed briefly.
Grape Flea Beetle
Grapevines are damaged by adult and by larval grape flea beetles.
Adult beetles are dark bluish-black and about 3/16 inch long.
They are usually the first insects of the growing season to
damage grapevines. Adult beetles feed on primary buds which then
cannot develop into primary canes, so crop yield is reduced.
Grape flea beetles breed in the vineyard, and females lay eggs on
various parts of the vine. Larvae are brown, spotted with black,
and about 1/4 inch long. They feed on the upper surface of
leaves and on developing flowers and buds, reducing yields.
Since both adults and larvae are easily seen vineyards should be
carefully monitored in the early season, paying special attention
first to cane and then to flower buds. Insecticides should be
applied when necessary.
Breeding Grapes for Florida (J. A. Mortensen)
1985 is our fortieth anniversary for the bunch grape breeding
program here at Leesburg. During this 40 years we have released
Lake Emerald (1954), Blue Lake (1960), Norris (1966), Stover (1968),
Liberty (1976), Daytona (1983), Conquistador (1983), and Suwannee
(1983). These bunch grapes are all resistant to Pierce's disease
and long-lived in Florida. All are seeded, though seedlessness has
been a breeding objective since 1961. One seedless test selection,
Florida BD8-77, is being reviewed today by the University Advisory
Committee for possible release to growers. BD8-77 originated from a
cross made in 1973 between Florida D4-176 (Norris x Schuyler) and
Florida F9-68 (Florida A4-23 x Perlette). Florida BD8-77 is
resistant to Pierce's disease, has larger clusters and better yields
than Stover, and has an acceptable level of seedlessness when
treated with gibberellic acid shortly after bloom.
The most promising seeded bunch grapes for potential release are
listed in the table below.
Date
Selection no. Parentage Color Sex Use Ripe
E18-63 W1521 x Aurelia It. gr. S.F. fresh, wine 7/12
H17-22 Norris x Schuyler purple S.F. red wine 7/17
H18-37 D6-148 x Cardinal It. gr. S.F. white wine 6/29
L9-10 21C-31 x F5-8 It. gr. S.F. white wine 7/22
BD12-49 E9-48 x Ark. 1105 It. gr. S.F. fresh 7/12
Very promising selections have been made from the vineyard based on
their first year of fruiting as seedlings:
Date
Selection no. Parentage Color Sex Seedless Ripe
BN7-18 DC1-39 x Lakemont golden Fem. yes 6/4
BN8-25 E18-63 x Lakemont golden S.F. yes 6/10
BN9-99 E18-63 x Lakemont It. gr. ? yes 6/19
BD7-93 E18-63 x Lakemont It. gr. ? no 6/17
BN9-60 E18-63 x Lakemont golden S.F. no 6/19
BN2-25 B3-83 x Lakemont golden ? no 6/18
All selections ripened in June and half were seedless. These are
being propagated for testing for resistance to Pierce's disease.
Other phases of our grape breeding include muscadine grapes (crosses
began in 1973), interspecific hybrids, and rootstock types. Tampa
was released in 1982 as a superior rootstock for bunch grapes in
Florida.
-9-
Gibberellin Applications on Experimental Seedless Bunch Grapes.
(M. C. Halbrooks)
The use of gibberellic acid (GA) and other plant growth
regulators to enhance the quality of seedless table grapes is
widespread and well documented in the literature. No research of
this type has been conducted, however, on the experimental
seedless cultivars for Florida. Specifically research is needed
on the effects of gibberellin on berry size, seed trace
development, cluster loosening, soluble solids and maturation.
In 1984, a preliminary study of the effects of gibberellin
applications on the experimental seedless table grape cultivar,
BD8-77, was conducted. One concentration of GA3, 75 ppm, was
applied at 4 stages of bloom development. Parameters measured
were:
1. number of large vs. small berries per bunch,
2. berry weight,
3. seed number per berry,
4. seed weight per berry,
5. seed number per cluster.
Significant findings of this study are shown in Table 5. Berry
size was greatest in clusters which received GA3 applications at
capfall plus 14 days (Table 5). Seed weight, however, was lowest
in clusters which received GA applications at 75% capfall, 100%
capfall or 100% capfall plus days. These results suggested
that GA applications made at early stages of bloom development
effectively diminished seed weight; while later applications
produced enlarged berries.
Research conducted in other table grape producing regions
indicates successive applications during bloom development and
varying concentrations of GA in solution were important factors
in achieving the combined effect of a loosened cluster with large
berry size and reduced seed traces. An additional factor to be
considered is girdling, removal of a thin section of bark around
the trunk of the vine, which is a common practice in table grape
producing regions of California to enhance berry size and soluble
solids.
In 1985, a factorial experiment utilizing two experimental
seedless bunch grapes, BD8-77 and F9-68, was conducted to
evaluate the effect of varying concentrations of GA3 made at 4
stages of bloom development.
The treatments were:
A. 4 concentrations of GA -
1. 38 ppm
2. 75
3. 150
4. 300
-10-
and
B. 4 stages of bloom development -
1. 100% capfall
2. capfall + 7 days
3. capfall + 14 days
4. capfall + 21 days,
made with all treatment combinations. Parameters to be measured
were:
1. berry weight
2. seed weight
3. cluster length
4. cluster looseness
5. soluble solids
6. incidence of berry cracking
7. indicence of shot berry
The grapes were harvested June 23 and data is currently being
recorded.
Table 5. Effect of gibberellin applications on berry weight and
seed weight.
I
Stage of bloom Berry weight "(g) Seed weight/berry (mg)
development
Control 1.1 + 0.1 14 + 2.5
75% capfall 1.3 + 0.1 2 + 2.5
100% capfall 1.2 + 0.1 0.8 + 2.5
capfall + 7 days 1.5 + 0.1 5 + 2.5
capfall + 14 days 1.9 + 0.1 13 + 2.5
Use of Tissue Culture for Production of Grape Varieties Adapted
to Florida. (D. J. Gray)
Tissue culture-related research is being conducted in order to
expedite the establishment of improved grape varieties adapted to
Florida. Three distinct research projects currently underway are
discussed below.
Rapid Micropropagation of Economically Important Varieties.-
The potential of grape as an alternate crop on surplus frozen
citrus land suggests that the need for desirable planting stock
may increase rapidly. It may not be immediately possible for
nurseries to meet this need. Tissue culture micropropagation is
a method that can be used to produce plants at a rate far in
excess to what is currently possible in grape nurseries.
-11-
The micropropagation technique is relatively straight forward.
Shoot tips are introduced into culture and are induced to branch
prolifically. Each branch is either removed and rooted,
producing a single plant, or is induced to produce more branches.
Thus, a continuously branching culture is maintained and new
plants harvested as needed. We have, to date, established 28
species, hybrids and/or cultivars in this culture system. Some
respond very well, whereas others branch less often. Ongoing
research in this area will concentrate on optimizing
micropropagation methodology for our most promising cultivars.
Rescue of Progeny From Seedless x Seedless Crosses.
Conventional breeding of seedless grapes is complex and tedious
because crosses between seedless cultivars do not yield viable
seeds. To circumvent this problem, breeders now cross seeded
with seedless lines hoping to recover a seed that ultimately
produces a seedless vine. This process typically takes ten or
more years to accomplish. Using tissue culture, it is possible
to rescue the young seed from seedless x seedless crosses and
promote the development of normal plants. In this manner, tpe
seedless trait is concentrated within one breeding cycle. Plants
are produced in a few months and then field tested. Total
development time is estimated to be four years.
To date, we have cultured approximately 6,000 embryos in a
specific medium-growth regulator regime. These embryos are the
results of controlled pollinations between various seedless
lines. The culture period is still in progress and we are
waiting to determine the results of our efforts.
Selection of Pierce's Disease Resistant Mutants.
Pierce's disease (PD) is the major factor limiting the
establishment of high quality European and North American grape
varieties in the Southeast. All bunch grapes currently grown in
Florida are the product of crosses between these quality PD
susceptible grapes and low quality but resistant native grapes.
The breeding that this entails has taken a very long time because
repeated crossing and evaluation are needed to ultimately select
a vine that retains the quality of one parent with only the
resistance of the other.
Plant tissue culture offers the opportunity to completely
circumvent the conventional approach by selecting resistant
mutations directly from quality grape varieties without use of
native species. In this approach, cultures containing large
populations of spontaneously mutating cells are challenged with
PD toxin. Only those rare mutant cells resistant to toxin are
able to survive and grow. Eventually cultures composed
completely of resistant cells are produced. If a high quality
but susceptible variety is used as the culture source, an
identical, high quality but now resistant cultivar is the result.
-12-
Therefore, the best European and American cultivars could be
expeditiously introduced into Florida without conventional
breeding.
Development of this system is one of the long term research goals
of our program. Several separate requirements must be met in
order to be successful. Although grape micropropagation as
described above is routine, regeneration from single cells is
much more difficult. Methodology to standardize toxin extracts
must also be developed, although it is now known that crude
extracts inhibit cell cultures. Thus far, we have obtained
regeneration from single cells of only one species, Vitis longii.
This is a native grape from the Texas-Oklahoma region and has no
economic use in Florida. However, this species is susceptible to
PD so that we can use it in advanced experimentation on resistant
mutation selection until we develop cultures of more desirable
grapes.
^; L L
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