Cucurbitaceae 94: Evaluation and Enchancement of Cucurbit
South Padre Island, TX November 1 - 4, 1994
Poster Presentation Abstracts
#1 A Database for Cucurbita Cultivars.
Thomas C. Andres, Cornell University.
The naming, classification, and systematics of the diverse
commercial varieties of Cucurbita is in need of better
organization. Popular cultivar groups, such as the vegetable
marrows and zucchinis, have been split into so many names that
some may not represent distinct varieties. On the other hand,
the same cultivar names are sometimes applied to different
cultivars. Cultivars are sometimes misclassified to species.
To help sort through the confusion two connected databases
were set up using the software program FileMaker Pro, which
is available on both Macintosh and Windows platforms. One database
is a compilation of over 100 seed companies and their addresses,
primarily from North America, that carry Cucurbita varieties.
The other consists of information on the Cucurbita varieties
themselves compiled from the seed company catalogs. This latter
database includes over 30 fields of descriptors, uses, origins,
taxonomy, and a scanned image field. Problems arise from the
dependence on seed company descriptions, such as the exaggeration
of the desirable traits, the flesh sweetness and deep orange
color being primary examples. In the future the database should
be corrected with data from unbiased variety trials. Also,
additional fields may be added, such as diagnostic molecular
markers. These databases may be expanded for use by various
cucurbit professionals, e.g., for variety registrars to conveniently
sort through a large amount of information, or for extension
agents to look up the availability or suitability of a particular
cultivar for a particular need. Through use of the cultivar
database, breeders may find that certain advantageous combinations
of characters have or have not been bred for.
#2 Observations of Triploid Melon under Intensive Greenhouse
Management in Japanese Hydroponic Production System.
Jeffrey Adelberg, Department of Horticulture, Clemson University,
Clemson, SC 29634; Michiko Takagaki, University Farm, Faculty
of Horticulture, Chiba University, 6-2-1 Kashiwanoha, Kashiwa,
Chiba 277 Japan.
Two clones of melon (Cucumis melo L.) from the same
parental tetraploid line, 'L-14 x B', were prepared in tissue
culture for transplant. Rooted microcuttings were acclimatized
to greenhouse conditions in burnt rice hull rooting medium.
Plants were raised to approximately the same size as diploid
seedlings in hydroponic nursery culture. Plants were grown
to maturity in rock wool (RW) or using nutrient film technique
(NFT) under natural light (March to July) with 20-30
C day temperature and 15-20 C night temperature. Vines were
trained to single vertical leader and lateral branches were
removed below the tenth node. Manual pollination from the commercial
variety, Amos, grown in row was used to set fruit on nodes
11-20. Fruit was thinned to one per vine and all lateral branches
were pruned at the second node. Tops of vines were removed
above the 25th node. The triploid clone '(L-14 x B) x Mainstream'
had set fruit after five to six weeks in the production house.
This period coincided with the fruit setting period for the
diploid variety, Amos. The other triploid clone, '(L-14 x B)
x L-14', had set fruit on only about 50% of the vines within
this time period. Triploid plants from the clone '(L-14 x B)
x Mainstream' bore fruit two to three weeks earlier than Amos.
From the vines of '(L-14 x B) x L-14' which had set fruit,
ripening was about seven days earlier than Amos. Triploid fruit
were round, but were also smaller and had lower soluble solids
than Amos on either hydroponic matrix. Soluble solids within
fruit of both triploid clones was lower in flesh adjacent to
seed cavity than in the central portion of the flesh. This
distribution was unlike Amos. Seed were abundant in both triploid
clones, and embryos were formed in many of the seed. Fruit
from diploid and triploid plants grown on organic soil under
the same management practices varied little from the hydroponically-produced
fruit in size, shape, or soluble solids. Fruit cracking was
not observed in any of the triploid fruit evaluated. Flesh
color and netting of the triploid clones was not what would
have been predicted by current genetic models.
#3 Generating Tetraploid Watermelons From Tissue Culture.
Xingping Zhang and Bill B. Rhodes, Department of Horticulture;
Halina T. Skorupska, Department of Agronomy and Soils and Department
of Biological Sciences; William C. Bridges, Department of Experimental
Statistics, Clemson University, Clemson, SC 29634.
More tetraploid watermelon varieties are needed to meet the
increasing demands of hybrid triploid watermelon cultivars.
This research was conducted to develop an efficient in vitro
system for generating tetraploid watermelons. Cotyledon tissue
of five genotypes was used as the explant to regenerate plants.
Murashige and Skoog (MS) medium with 10 uM BA was used for
shoot organogenesis and shoot proliferation, and MS medium
with 10 uM IBA was used for rooting shoot. Incorporation of
colchicine in the regeneration medium during the first week
of shoot organogenesis significantly increased the frequency
of tetraploids in the regenerated population. The effects of
genotype and cotyledon age on the frequency of tetraploid were
also observed. The regenerated tetraploids are characterized
by relative wider leaf shape with over-lapping round lobes,
larger pollen grains as determined by surface area, pollen
grains with four colpi, and considerably reduced seed number
per fruit. The regenerated tetraploids were first screened
at transplant stage in the greenhouse according to leaf morphology,
and then confirmed by flower and pollen characters, and/or
the nuclear DNA content using flow cytometry. The tetraploid
lines developed from tissue culture are being increased, and
the triploids derived from the tetraploids are being evaluated.
A practical protocol for generating tetraploid watermelon using
tissue culture is described.
#4 Fluoroscopy as a Non-Invasive Method for Detect ing Hollowheart
and Seeds in Watermelon Fruit.
Fred T. McCuistion Jr.1. Gary W. Elmstrom2.
P Abbott3. B. Steinbach3. B Faile4. Norman Ackerman5. Lisa Neuwirth5. and Crispin Spencer5 1Department of Horticultural Sciences, IFAS-University of Florida, PO
Box 110693, Gainesville, FL 32611-0693; 2Central
Florida Research and Education Center, IFAS-University of Florida,
5336 University Avenue, Leesburg, FL 34748; 3Shands
Hospital, Department of Radiology, University of Florida, College
of Medicine, PO Box 100374, Gainesville, FL 32610-0374; 402052
Melanie St., Fruitland Park, FL 34731; 5Department
of Small Animal Clinical Sciences, College of Veterinary Medicine,
University of Floridas PO Box 100126, Gainesville, FL 32610-0126.
The occurrence of hollowheart (HH) in watermelons is a negative
quality factor which can cause a reduction in marketable yield.
However, the presence of HH is not readily obvious by external
examination. In addition, the presence of hard seeds in triploid
melons is undesirable. The purpose of this study was to determine
the technical feasibility of a non-invasive method of detecting
HH and hard seeds in watermelons in order to assure quality.
In this study seeded and seedless watermelons were scanned
by magnetic resonance imaging, ultrasound, xerography, fluoroscopy,
and mammography. The best technique for detecting both HH and
seeds was xerography; however, the need for developing a print
makes it impractical. Fluoroscopy was the best technique for
correctly and accurately identifying the size and occurrence
of HH in seeded and seedless fruit. Seeded melons were easily
distinguished from triploid, seedless melons. The latter contain
as many as S to 10 hard seeds. This technique failed to identify
hard seeds in 15 of 17 triploid melons which contained 1 to
3 hard seeds.
#5 A Rapid Method for Cleaning Seed from Single Watermelon
Perry E. Nugent, USDA-ARS, U. S. Vegetable Laboratory, Charleston,
Watermelon seed has traditionally been cleaned by fermenting
the mashed flesh and seed mixture. This is a time consuming,
messy, and smelly method. If the fermenting flesh is not cleaned
at the right time, dead seed can result. Our method involves
using enough water to cover the chopped flesh in a 23 liter
pail with a tight fitting lid and a cordless electric drill
with a special blade. Seed from a large 10-14 kilogram watermelon
can be cleaned and ready for drying in 5 minutes. Results of
a germination test show that seed cleaned by our method germinate
as well as or better than those cleaned by the fermentation
#6 Genes Controlling Watermelon Seed Size.
Xingping Zhang, Bill B. Rhodes and Huilin Wang Department
of Horticulture, Clemson University, Clemson, SC 29634; William
C. Bridges Department of Experimental Statistics, Clemson University,
Clemson. SC 29634.
Seed size is critical for yield and quality of edible seed
watermelons. The seed size of tetraploid and diploid parents
determines the size of the undeveloped seed coat in the triploid
hybrid. Consumers prefer small undeveloped seed in triploid "seedless" watermelons.
This research attempted to determine number of genes involved
in watermelon seed size in more divergent parents than in previous
studies. The very large "edible seed" parent has seed more
than 40 times heavier and more than 4 times longer and wider
than the very small "tomato seed" parent. These two parents
were used to develop Fl's, BCI, BC2 and
F2 populations. A significant correlation (rp=0.97572) was found between seed length and seed weight. Seed length
was consequently used as the criterion of seed size. The data
obtained from 15 individuals of each parents and Fl's;
109, 115 and 563 individuals of BCI, BC2 and
F2, respectively, showed that there were only
2 major loci controlling seed length. However, there was no
individual with seed size same as the large-seeded parent found
either in the F2 population with 563 individuals or in the BCI population
with 109 individuals, because of the affect of the modifying
genes. The genotypes for "tomato seed" watermelon and "edible
seed" watermelon are LLss and llSS, respectively. Extremely
small seed can be more easily selected than the extremely large
seed because the function of the modifying genes make seed
smaller. The data also indicated that small seed was associated
with an undesirable trait, vivipary. These results should be
very useful for in breeding cultivars with different seed sizes.
#7 Short Sequence Repeat (SSR) DNA Markers in Watermelon.
R.L. Jarretl, N. Bowenl, Z. Liul,
S. Kresovichl and P. Cregan2, 1USDA/ARS/SAA, Plant Genetic Resources Unit, 1109 Experiment Street,
Griffin, GA 30223 and 2USDA/ARS/SARL, BARC-West,
Beltsville, MD 20705.
A TaqI/ClaI genomic library of watermelon (Citrullus
lanatus) was constructed in pGEM7Z(+), cloned into E.
coli strain HB109 and screened for the occurrence and frequency
of tandemly repeated dimer and trimer repeats including;
(GT)n, (AT)n, (CT)n, (ATT)n and (CTT)n. Approximately 10,000
recombinant colonies were screened and 84 SSRs were identified
and isolated. SSR-bearing plasmids were sequenced on an automated
(ABI) DNA sequencer and primer pairs flanking the SSR loci
were selected using commercially available software. Primers
pairs are currently being tested for their efficacy in detecting
SSR polymorphisms among a range of watermelon plant introductions
#8 Inheritance of Resistance to Zucchini Yellow Mosaic Virus
in 'Egun' WatermelonControlled by a Single Dominant Gene.
George E. Boyhan, Joseph D. Norton, Oyette L. Chambliss,
James M. Dangler, and and Paul A. Backman, Department of Horticulture,
Department of Plant Pathology, and Alabama, Agricultural Experiment
Station, Auburn University, AL 36849.
The mode of inheritance of resistance to zucchini yellow
mosaic virus (ZYMV) in 'Egun', was found to be controlled by
a single dominant gene. F2 populations segregated
166 resistant to 50 susceptible based on visual ratings.A X2 value
of 0.30 indicated that this was not significant for a 3:1 ratio.Backcrosses
of the F1 to 'AU-Producer', the susceptible parent,
resulted in a ratio of 61 resistant to 51 susceptible not different
from a 1:1 ratio with a X2 value of 0.72. ELISA
testing showed a higher frequency of susceptibles in the F2 then
would be expected by a single dominant gene. There were 149
resistant and 72 susceptible individuals in the F2 population with a X2 of 6.37. The backcross to 'AU-Producer'
had 52 resistant to 37 susceptible individuals which is similar
to a 1:1 ratio (X2 of 2.20). A bioassay against
'Pavo' summer squash confirmed that a single dominant gene
controls resistance in 'Egun' to which the symbol ZYM is assigned.
It is conjectured that the ELISA test is able to detect the
coat protein even though no visual or bioassayed symptoms are
#9 Comparison of Triploid and Diploid Watermelon Cultivars
for Susceptibility to Bacterial Fruit Blotch.
D. L. Hopkins and G. W. Elmstrom, University of Florida,
Central Florida Research and Education Center, 5336 University
Avenue, Leesburg, FL 34748.
In field tests, one hill per row of each watermelon cultivar
was inoculated four weeks after planting with the fruit blotch
bacterium by misting a bacterial suspension on the foliage
until runoff. There were no obvious differences in susceptibility
of the foliage to fruit blotch. In hot, humid weather, the
symptoms spread and developed on all cultivars. In general,
fruit of diploid watermelon cultivars appeared more susceptible
than that of triploid cultivars. In 1993, Charleston 6ray and
Jubilee with 54 and 55% fruit symptoms, respectively, had significantly
more fruit blotch than any of the triploids. Incidence of symptoms
in the triploid ranged from 15% in Tri X-313 to none in Queen
of Hearts. Because of dry weather, there was much less fruit
blotch in the test in 1994, but Charleston Gray and Jubilee
with 42 and 19% fruit symptoms, respectively, again had significantly
more fruit blotch than any of the triploids. In most of the
triploids, there were no fruit symptoms. With the triploids
and the diploids, there seemed to be a relationship between
rind color and incidence of fruit blotch. The light-green,
Charleston Gray- type rind appeared most susceptible and the
dark-green, Sugar Baby-type rind the least susceptible. However,
bacterial fruit blotch symptoms can develop on all rind color
#10 Yellow Vine Disease of Watermelon and Cantaloupe in
Central Texas and Oklahoma.
B. D. Bruton*, S. D. Pair, and E. V. Wann, USDA-ARS, P. O.
Box 159, Lane, Oklahoma 74555.
Incidence of yellow vine appears to be restricted geographically
to the cross timbers region of Texas and Oklahoma and tends
be more severe in watermelon than in cantaloupe. Yellow vine
in watermelon and cantaloupe typically begins to develop 10-15
days prior to harvest. Affected plants turn from green to a
bright yellow within about a 3 day period. Over the next 7-10
days, the leaves gradually collapse giving a blighted appearance.
Root rot is not associated with yellow vine, although there
is a distinct discoloration of the phloem particularly in the
crown and root system. Crops planted in April and early May
tend to be affected most (50% or more diseased plants) whereas
those planted later normally have less than 5% yellow vine.
Evidence suggests that the disease may be caused by a bacterialike
organism vectored by an insect. Although not practical, weekly
insecticide applications slow the rate of disease development.
The only source of resistance identified to date is the tetraploids
used for seedless watermelon production.
#11 Disease Resistant Tetraploid Citrullus lanatus.
O. J. Eigsti. American Sunmelon, 1602 Winsted, Goshen, Indiana,
Two tetraploid lines show excellent growth and vigor ln plots
that have had continuous watermelon culture for forty generations.
These colchiploids were developed from diploid cultivars, Calhoun
Gray and Wilt Resistant Congo, respectively. Both tetraploids
show promise for producing disease resistant,as well as, excellent
quality triploid seedless hybrids. More detail with photos
will be given at the poster session.
#12 Screening Cucumber and Watermelon for Resistance to Anthracnose, Colletotrichum
L.A. Wasilwa, J.C. Correll, and T.E. Morelock, Depts. of
Plant Pathology and Horticulture, University of Arkansas, Fayetteville,
Colletotrichum orbiculare, the causal organism of
anthracnose on cucurbits, is composed of three genetically
distinct races which can be differentiated using virulence
and a genetic test for vegetative compatibility. Race 1 consists
of cucumber and cantaloupe isolates which belong to vegetative
compatibility group (VCG)l and VCG 3; race 2 consists of watermelon
isolates in VCG 2; and race 2B consists of watermelon and cucuzzi
gourd isolates also in VCG 2. Cucumber and watermelon cultivars
and breeding lines were evaluated for resistance to race 1,
2 and 2B. For the greenhouse tests, cotyledons and plants with
two to four true leaves were inoculated with a spore suspension
(8 x 10' spores/ml) of a composite of six geographically diverse
race 1> race ' or race 2B isolates. For the field tests
cucumber cultivars were inoculated with race 1 and watermelon
cultivars with race 2 and race 2B. A spore suspension of 5
x 10@ was used for the Field inoculation tests. In the cotyledon
tests, most cucumber and all watermelon cultivars were highly
susceptible to race 1 and race 2, respectively. Many cucumber
cultivars were moderate to highly resistant to race 2, and
most watermelon cultivars were highly resistant to race 1 and
race 2B. The watermelons that were highly resistant to race
1 were also highly resistant to race 2B. Cucumber cultivars
with high resistance to race 2 in the cotyledon tests also
had high resistance to race 1 in the true leaf and field inoculation
tests. While the watermelons with high resistance to race 1
and race 2B in the cotyledon tests were highly susceptible
to race 2 in the greenhouse true leaf inoculation tests. Field
inoculation tests to evaluate selected watermelon cultivars
for field resistance to race 2 and race 2B also have been conducted.
For cucumber cultivars. the watermelon pathogen (race 2) is
more effective for screening cucumber cultivars for resistance
at the cotyledon stage as the cucumber pathogen (race 1) is
too aggressive under greenhouse inoculation conditions. For
watermelon, the cucumber pathogen (race 1) or the cucuzzi gourd
and watermelon pathogen (race 2B) can be used to screen for
resistance to watermelon in the greenhouse cotyledon inoculation
#13 Screening the Cucumber Germplasm Collection for Nine
Todd C. Wehner, Department of Horticultural Science, North
Carolina State University
Raleigh NC 27695-7609.
The cucumber (Cucumis sativus L.) germplasm collection
was evaluated for 9 horticultural traits. Traits included fruit
yield, keeping ability, early flowering, root size, and resistance
to nematodes, gummy stem blight, anthracnose, belly rot and
chilling. These evaluations were intended to provide plant
breeders with a starting point for development of cultivars
with improved performance for the traits. The germplasm collection
consisted of approximately 800 plant introduction accessions,
common breeding lines, and new and obsolete cultivars (collectively
referred to as cultigens). Since not all cultigens produced
early pistillate flowers, yield was evaluated by crossing all
cultigens with Gy 14 to make gynoecious hybrids. Plots in each
of the 3 replications were harvested once-over when 'Calypso'
reached 10% oversized fruits. Total, marketable and early fruit
number were counted on each plot. Three fruits per replication
were also tested for keeping ability by storing at room temperature
for 3 weeks. Fruit shriveling (rated 0 to 9) was the trait
with the best stability of those measured. Days to first flower,
root length, and nematode galling (from Meloidogyne incognita and M.
arenaria) were evaluated on plants grown in 150 mm diameter
pots in the greenhouse with 3 replications of 1 plant each.
Resistance to gummy stem blight and anthracnose were evaluated
in the field under natural inoculum load. Belly rot was evaluated
using artificially inoculated fields. Chilling resistance was
measured on seedlings grown at 22/18 C and chilled at 4 C for
7 hours under full light in controlled environment chambers
in the NCSU phytotron. Data on cultigen performance will be
submitted to the USDA Germplasm Resources Information Network
database for use by researchers. Further research is needed
to verify the performance of the cultigens evaluated, and to
measure the inheritance of each trait.
#14 Optimalization of Cucumber (Cucumis sativus L.)
Haploid Production and Doubling.
Katarzyna Niemirowicz-Szczytt, Najat Mustafa Faris, Vesselina
Nikolova, Monika Rakoczy-Trojanowska, Stefan Malepszy, Department
of Genetics and Hortic. Plant Breeding, Warsaw University of
Agriculture, Nowoursynowska Str. 166; 02-766 Warsaw, Poland
Optimal conditions for cucumber haploid production were evaluated.
Cucumber haploid plants were obtained by pollination with irradiated
pollen and by in vitro culture of excised embryos. Both, donor
plant genotype ( four F1 hybrids and four inbred
lines in Experiment I and one F1 hybrid and two inbred lines
in Experiment II) and doses of gamma irradiation (0.2 and 0.3
kGy in Experiment I and 0.1, 0.2 and 0.3 kGy in Experiment
II) were tested. The number of embryos obtained varied according
to genotype of donor plant, and was generally higher among
F1 hybrids. Although embryo yield was best with
the lowest dose of irradiation, the number of mature plants
obtained was similar with all doses. In order to obtain dihaploids,
an efficient plant regeneration method via callus formation
from haploid leaf explant has been developed. Regenerated plants
were grown to maturity in the greenhouse. Out of 16 flowering
plants, 56% produced normal, viable pollen grains typical for
diploids. Chromosome analysis of these plants indicated that
all of them were diploid.
#15 RFLP Mapping of Locus acr Controlled Sex Expression
S. Matsuura and Y. Fujita, Tohoku Seed Co., Ltd., Himuro,
Utsunomiya, Tochigi 321-32 Japan.
In cucumber breeding, the sex expression is one of the important
characters and the genetic analysis of this phenotype was studied
(Kubicki, 1969). Based on his report, this phenotype is controlled
by multiple allele of the locus acr. In order to
select the gynoecious plants at nursery stage in segregating
population, we searched for RFLPs in the local region of this
locus. From the screening of 308 genomic and 258 cDNA clones
of cucumber, eight polymorphic clones were obtained between
two parental lines. From link-age analysis using a F2 generation derived from the cross between these parental lines, RFLP
clones, P-051 and C-396, were linked
with the locus acr. Recombination values were 20.5+5.8%
between P-051 and acr, and 30.8+6.6% between C-396 and acr. Almost of cucumber
cultivars in Japan are monoecious or monogynoecious and we
are going to breed the gynoecious type. There were two alleles
on the locus P-051, the distribution of the allele was investigated in some inbred
lines which did not have the gynoecious gene and in some donor
lines of the gynoecious ones. Since both alleles were observed
not only in some donor lines but also in a recipient lot, it
was clear that P 051 would be a useful marker for
the gynoecious breeding of cucumber.
#16 Effect of Explant Orientation on Cotyledon Culture
of Cucumis sativus L.
Anup K. Misra and S.P. Bhatnagar, Department of Botany, University
of Delhi, Delhi-110007, INDIA.
Cucumber (Cucumis sativus L.), a member of the family
Cucurbitaceae one of the important vegetable crops of the world,
which is originated in India. It is widely grown throughout
the tropics and sub-tropics. Therefore, the potential usefulness
of cucumber breeding program is apparent. The application of in
vitro methods in this species is especial promising for
the improvement because, here genetic variability is limited
by sexual incompatibility with other taxa of the same family.
Two halves of the cotyledon, derived from seedlings of different
ages (0,1,3,5,7,10 and 14 days) were cultured on MS medium
supplemented with different cytokinins. Amongst the tested
concentrations MS with 10 uM BAP (SIM = shoot induction medium)
proved to be best treatment for shoot differentiation from
excised cotyledon of 1-day-old seedling. For studying the effect
of explant orientation on shoot differentiation, entire cotyledons,
their halves (apical, basal and longitudinal) and pieces (upper,
middle and lower) derived from l-day-old seedling, were cultured
on SIM in different orientation. Total ten types of orientation
were studied. The shoot bud differentiation was maximum (91.6%)
when cotyledon was implanted with its basal/petiolar end embedded
in the medium. The shoot buds differentiated directly from
the petiolar end. In other orientations shoots differentiated
in low frequency. Thus, the orientation of explants on the
medium significantly affected the frequency and mode of differentiation.
Shoot buds transferred on MS basal medium for elongation. All
these shoots rooted on MS supplemented with 1 ,uM IBA. The
plantlets were transferred to plastic pots containing a mixture
of sand and garden soil (1:1). After two weeks these plants
were transferred to field with 80% survival rate. These plants
produced normal flowers and fruits.
#17 Acquired Disease Resistance Response in Pickling Cucumbers
is Influenced by Plant Development and Cultural Factors.
Irvin Widders1, Lavetta Newell1 and Ray Hammerschmidt2, Departments of 1Horticulture and 2Botany
and Plant Pathology, Michigan State University, East Lansing,
Acquired physiological resistance to angular leaf spot (Psuedomonas
syringae pv. Iachrymans) and anthracnose (Colletotrichum
lagenarium) has been demonstrated in pickling cucumbers
through foliar applications of 2,6- dichloroisonicotinic
acid (CG-41396, Ciba Geigy ). The objectives of the current
study were to investigate the effects of developmental and
cultural factors on the ability of cucumber plants to develop
acquired disease resistance. Pickling cucumbers (cv. Flurry,
Asgrow Seed Co.) were sprayed foliarly with CG-41396 (35
ppm) or CuS04 (0.9 Kg/A) at various stages of vegetative
development. At anthesis, all plants were foliarly inoculated
with Psuedomonas syringae pv. Iachrymans. A single
application of CG-41396 at the 2nd true leaf stage was found
to be equally effect in reducing the incidence of angular
leaf spot at harvest time as three applications of either
CG-41396 or CuS04 over a 3 week period. Lesion densities,
as measured on leaves 4 and 8 counting from the vine apex,
were 60 and 20% lower, respectively, than water treated controls.
In a second experiment, cucumbers were planted at two different
times so that foliar applications could be made to plants
at different stages of development (1st and 6th true leaf
stages), thus avoiding potential environmental interactions.
The highest level of acquired resistance was achieved in
plants treated with CG-41396 at the 1st true leaf stage.
Lesion densities of angular leaf spot were 45 and 77% lower
in leaves 4 and 8, respectively, than in controls. Within
row spacing and nitrogen fertilization rates were also found
to influence the induced resistance response. We postulate
that the ability of cucumber plants to respond physiologically
to CG-41396 and to develop acquired disease resistance is
influenced positively by plant vigor at the time of application.
#18 Yield of Pickling Cucumber as Influenced by Black
Plastic Mulch and Plant Population.
Jonathan R. Schultheis, Department of Horticultural Science,
North Carolina State University, Ralelgh NC 27695-7609.
The use of black plastic with fertigation has improved yields
of many vegetable crops. This study was conducted to improve
pickling cucumber yields by optimizing cultural practices on
black plastic mulch. In an April 22, 1994 planting in Clinton
SC, the effects of three plant populations (21.5, 43.0 and
86.0 thousand plants/ha) in four spatial arrangements (2 rows/bed,
1 row/bed, 2 plants/hill, l plant/hill), culture on bare ground
versus black plastic mulch, and 2 cultivars (Napoleon and Calypso)
were evaluated for yield potential. Fruits were harvested 10
times, twice per week. Differences in yield were primarily
due to main effects; cultivar, mulch (black plastic versus
bare ground), and plant population. Early marketable yields
were increased nearly l.1 Mg/ha when grown on black plastic
mulch compared with plantings not made on plastic. 'Napoleon'
yielded 56% more marketable fruit than 'Calypso ' when early
and total yields were compared . More truit from grades l and
2 were obtained in the initial two harvests from the highest
plant population compared with the lowest plant population.
Total marketable yields averaged 31.4 Mg/ha on black plastic
compared with 19.6 Mg/ha on bare ground. Growing cucumbers
on black plastic mulch with the cultivar Napoleon resulted
in the highest yields.
#19 Weed Management Studies for Processing Cumbers.
John 0'Sullivan and William J. Bouw, Horticultural Experiment
Station, Simcoe-, Ontario
Weed competition is one of the major factors limiting yield
of processing cucumbers. Currently, there are few registered
herbicides available for cucumbers and those that are available,
provide inconsistent results. The objective of this research
was to develop information on the selectivity of new herbicides
such as clomazone (Command) and bentazon (Basagran) for use
on processing cucumbers. Clomazone was applied at 0.24 (0.5
L) to 0.48 kg/ha (1.0 L/ha). The herbicide was incorporated
shallow to ensure that the herbicide was placed above the cucumber
germination zone. Bentazon was applied at 0.6 (1.25 L/ha) and
0.84 (1.75 L/ha) postemergence. Clorathal dimethyl (Dacthal),
applied shallow preplant incorporated, and naptalam (Alanap)
postemergence were also evaluated. These treatments were compared
to the standard herbicide treatments available for cucumbers,
naptalam (Alanap) preemergence and ethalfluralin (Curbit) preemergence.
Clomazone caused a slight degree of crop injury to cucumbers.
The injury increased as the rate of application increased from
0.24 to 0.48 kg/ha. Clomazone combined with Clorathal dimethyl
caused substantial crop injury. This combination, however,
provided excellent control of Pigweed which is not controlled
by clomazone applied alone. Clomazone combined with naptalam
did not result in any increased crop phytotoxicity. Bentazon
caused some crop phytotoxicity. Data on total weed biomass,
broadleaf weed ratings, grass ratings and yield were also collected.
All herbicide treatments reduced weed biomass. Clomazone reduction
of weed biomass was dependent on the rate of application with
the maximum reduction at the highest rate of application. The
addition of naptalam postemergence to clomazone resulted in
improved weed control. These results show that clomazone could
be used as a selective herbicide for broadleaf and grass control
in processing cucumbers. The lowest rate of clomazone (0.24
kg/ha) in combination with ethalfluralin (preemergence) or
naptalam (postemergence) is especially effective for broadleaf
weed control with minimal crop injury and no significant yield
#20 Calcium Content of Fruit from Four Pickling Cucumber
Genotypes with Different Fruit Firmness.
Kevin L. Cook and James R. Baggett, Department of Horticulture,
Oregon State University, Agriculture & Life Sciences 4017,
Corvallis, OR 97331; August C. Gabert, Sunseeds, Research Station,
8850 5th Ave., Brooks, OR 97305.
The natural calcium content of cucumber tissue has a large
effect on the rate of tissue softening and the influence of
calcium applications on firmness retention during processing.
The objective of this research was to investigate whether genetic
variability for fruit calcium concentration existed in four
pickling cucumber genotypes which differ greatly in fruit firmness;
Pickling cucumbers 'Clinton', 'Armstrong Early Cluster', W744,
and WI1983 were planted in a complete randomized block experimental
design with three blocks at Brooks, Oregon in 1992. Standard
cultural practices and drip irrigation were used. Fruit cross
section samples approximately two cm thick from the center
of fruit 2.7-3.8 cm in diameter were taken and included exocarp,
mesocarp, and endocarp tissues. Samples were stored at -23.3
C, dried, ashed, and calcium content determined by atomic absorption
spectrophotometry by the Central Analytical Laboratory at Oregon
State University. Ten samples per genotype per block were used.
Genotypes were not significantly different in calcium content
on a dry weight basis (mg Ca/mg dry weight), however block
was highly significant (p < 0.0001). The genotype x block
interaction was not significant. The experiment was repeated
Ethylene production rate and postharvest shelf-life of melons
with diverse ripening phenotypes.
David W. Wolff and James R. Dunlap, Texas Agricultural Experiment
Station, The Texas A&M University System, 2415 E. Highway
83, Weslaco, TX 78596
Cucumis melo varieties show a great diversity
of ripening and abscission phenotype, ethylene production,
and postharvest keeping quality. As a preliminary step in the
development of melons with improved shelf-life and modified
ripening, we surveyed 100 genotypes of melons with diverse
ripening characteristics for ethylene production rate and shelf-life.
Genotypes representing seven melon types (Western shipper cantaloupes,
Eastern cantaloupes, Long shelf life cantaloupes [LSL], Charenteis,
Galias, Honeydews, Casabas) were planted in the field in a
randomized complete block with three replications. C. melo var. reticulatus and C.
melo var. inodorus were harvested 40 and 50 days
post-anthesis, respectively, and brought in the lab for ethylene
production measurement. Fruit at horticultural maturity were
also harvested and stored at room temperature. After seven
days, a postharvest decay rating (1 = complete rot and collapse
- 5 = no softening or decay) was taken to determine relative
shelf-life of the genotypes. Average ethylene production rate
ranged from 44.44 to 0.64 nl/hr/g for Eastern cantaloupes and
Casaba melons, respectively. A negative linear relationship
was observed between ethylene production rate and postharvest
decay rating. LSL cantaloupes had the lowest ethylene production
rate of the netted, orange flesh types. The relationship between
ethylene production rate and polymorphism for ACC oxidase cDNA
probe pMEL1 is being investigated.
Evaluation of melon germplasm for resistance to Monosporascus
root rot/vine decline.
David W. Wolff, Texas Agricultural Experiment Station, The
Texas A&M University System, 2415 E. Highway 83, Weslaco,
Monosporascus root rot/vine decline has been the
most devastating pathogen affecting melons in the Lower Rio
Grande Valley the past nine years. We conducted a field screen
of 130 melon cultigens to identify potential sources of host-plant
resistance to Monosporascus cannonballus. Seed were
sown in Speedling trays with inoculated or non-inoculated media.
Plants were transplanted into a field known to be highly infested
with Monosporascus cannonballus. Non-inoculated plots
were planted in rows that were fumigated with Telone II. Cultigens
were arranged in a randomized complete block with three replications
in each treatment (fumigated, non-fumigated). A disease symptom
rating (1 = complete death to 5 = no symptoms) was taken at
78 and 90 days post-transplanting. Disease symptoms were most
severe and occurred earliest in the inoculated, non-fumigated
plots. Natural infection by Monosporascus occurred in
the fumigated plots as over 95% of root samples collected contained
perithecia. At the second rating date, 108 of the 130 cultigens
tested were classified as moderately to highly susceptible
(Rating < 2.5). The four most resistant genotypes had a
second rating equal or close to 4.0 ('Galia', 'Deltex', 'Rocky
Sweet', 'Charlynne'). A group of 14 genotypes showed moderate
resistance with a second rating of 3.0. Included in this group
were 'Morning Ice', 'Doublon', 'Israeli', 'MR-1', 'Santa Clause',
and 'Primo'. The physiological stress of a concentrated fruit
set increases severity of the vine decline symptoms.
#21 Muskmelon Cultivar and Fruit Size Affect Beta-Carotene
Gene Lester, USDA-ARS and Frank Eischen, Texas A&M, Weslaco,
Five fully abscised 'Cruiser' and 'Primo' (Cucumis melo L.
var reticulatus Naud.) fruits from each commercial size class:
9's, 18's, 23's, and 30's; grown at 2 different locations;
2 different years; were assayed for Beta-carotene. Years and
location did not affect carotene content but cultivar and fruit
size did. Fruit carotene content was lowest in 'Cruiser' and
highest in 'Primo'. Regardless of cv. carotene content was
highest in size classes 12's and 15's versus all other sizes
and had a quadratic regression with fruit size. Percent fruit
moisture content was higher in 'Cruiser' than 'Primo' fruits
and regardless of cv. was high in all fruits sizes except 12's
and 15's. Percent moisture content had a quadratic regression
with fruit size and was negatively regressed with carotene
content indicating a fruit cell dilution effect. This relatively
low environmental (year and location) influence and relatively
high cultivar variability for beta-carotene suggests possible
genetic regulation for increasing this nutritionally important,
anti-cancer compound. However, fruit size should be considered
when determining a cultivar's Beta-carotene content.
#22 Potential Use of a Wild Melon (Cucxmis melo L.
var chito) as a Source of Useful Genetic Variation.
Javier Gonzalez R. ' Department of Agronomy, Autonomus University
of Tamaulipas, 87000 Cd Yictoria, TAM Mexico.
Mesoamerica is an important center of plant domestication.
However, landraces and wild plant relatives are rapidly disappearing,
together with their natural ecosystems. In addition, modern
agroecosystems are become more vulnerable to a number of stress
factors. Therefore, the objectives of this study were: 1) to
reduce genetic erosion by collecting wild germplasm, 2) to
transfer new genetic diversity to elite commercial varieties
of melon. In the summer of 1992, a wild melon identified as
belonging to the botanical variety chito was collected from
the central region of Tamaulipas, Mexico. It was crossed as
the female parent to the cultivated melon variety 'Durango'
(C. melo L var. reticulatus). Both parents were planted
under greenhouse conditions dunng the winter season of 1992.
The wild parent proved to be monoecious, white the cultivated
parent was andromonoecious. The former trait was dominant in
the F1 generation. This trait may be important
for hybrid seed production. Circumstantial evidence indicates
that the collected wild melon may be a source of tolerance
and resistance to saline environments, insects and foliar diseases.
The overall F1 phenotype was similar to the wild
parent, except for the presence of a slight fruit netting.
A modified backcross program may allow the development of more
stable varieties of cultivated melon.
#23 Genetic Transformation of a Recalcitrant Melon (Cucumis
melo L.) Variety.
Victor Gaba (1), Ester Feldmesser (1), Amit Gal On (1), Hadar
Yeheskel Antignus (1),(1) Dept. of Virology, ARO Volcani
Center, POB 6 Bet Dagan 50250, Israel; (2) Dept. of Plant Genetics,
Weizmann Institute of Science, Rehovot, Israel.
A range of kanamycin concentrations was tested for the inhibition
of adventitious bud formation in cotyledon explants of melon
(Cucumis melo L.) cv. Galia. Whereas regeneration in
cucurbits has been shown to be inhibited by kanamycin concentrations
of 25-150 mg/L, adventitious bud formation was only slightly
inhibited by concentrations of 250 mg/L kanamycin. Transformation
is only possible by particle bombardment of explants, using
350 mg/L kanamycin. Transformed melon material grows on kanamycin
selective medium, and an introduced gene is detectable by PCR.
Transformed shoots were recovered from 1% of bombarded explants.
#24 Development of molecular markers for genome analysis
in Cucumis melo.
Irina Kovalski, Leah Silberstein, Ruguo Huang and Rafael
Department of Life Sciences, Bar-Ilan University, Ramat Gan
Our laboratory is trying to develop a molecular marker system
for melons. This is done in collaboration with M.M. Kyle and
co-workers at Cornell University. Our first goal is to identify
a large set of polymorphic DNA marker (RFLPs and RAPDs) that
will be useful in marker-assisted breeding, genome mapping
and genetic studies. It is important, for this purpose, to
assess the degree of DNA polymorphism within Cucumis melo
. We are currently surveying an initial panel of 13 varieties
that represent diverse melon types using RAPDs and repetitive
DNA probes; more accessions may be included in the future.
In addition, we are developing a mapping population based on
a cross between the well-known PI 414723 and Topmark. This
F2 population segregates for WMV, ZYMV PRV and powdery - mildew resistance
genes, and for a number of morphological characters. We detected
moderate amounts of polymorphism between these two parental
lines, using melon PstI-genomic clones as RFLP probes. Cucumber
cDNA probes are tested as well. More polymorphism can be detected
with the RAPD technique, but reliability of such markers for
F2 mapping needs to be confirmed in our system.
We are trying to look also at other pairwise combinations of
germplasm items for molecular mapping. Suggestions of Conference
Attendants regarding their favorite accessions to be included
in our analysis are most welcome!
#25 Application of RAPD and SSR Analyses to the Identification
and Mapping of Melon (Cucumis melo L.) Varieties.
Nurit Katzir1, Yael Danin-poleg1, Galil Tzuri1, Zvi Karchi1
, Uri Lavi2 and Perry B.Cregan3, 1 Department of Vegetable
Crops, Newe Ya'ar Research Center, Agricultural Research Organizatio
P.O.B. 90000, Haifa 31900, Israel., 2 Institute of Horticulture,
Agricultural Research Organization, Volcani, Centerl, P.O.B.
6, Bet-Dagan 50250, Israel., 3 USDA-ARS, BARC-West, Beltsville,
MD 20705, USA.
RAPD and SSR analyses were applied to several accessions
and varieties of melon belonging to the following groups: muskmelon
('Galia' type cultivars and Dulce cv.), casaba (Q36 cv.), pickling
melon (P15-S5), PI414723 and Freeman's cucumber. Two hundred
and twenty arbitrary 10-mer oligonucleotide primers were screened
for their ability to detect polymorphism between and within
groups. Eighty four primers demonstrated polymorphism between
groups. Within the 'Galia' type group, polymorphism was much
lower. Only 1 of the 28 primers tested showed polymorphism
between the Israeli 'Galia' and 'Arava' cultivars. In search
for SSR (microsatellite) markers, a genomic library of melon
('Noy Yizre'el') was screened with dinucleotide probes (CT,
GT, GC). Positive clones (mainly CT) were identified. A pair
of primers was subsequently synthesized for each SSR. PCR amplification
of one SSR is presented, clearly demonstrating polymorphism
between and within groups, including 'Galia' and 'Arava' cultivars.
In order to obtain a genetic linkage map of melon, an F2 segregating
population (PI414723-S5 X Dulce cv.) was established. Twenty
RAPD and SSR markers were so far analyzed, along with 20 conventional
#26 Molecular Polymorphism Between Two Cucumis melo Lines
and Linkage Groups.
Sylvie Baudracco-Arnas, Michel Pitrat., INRA, Station d'Amilioration
des Plantes Maranchhres, BP 94, 84143 Montfavet Cedex, France.
Melon inbred line PI 161375 ("Songwhan Charmi"), which possesses
monogenic disease resistances ( races 0 and 1 of fusarium wilt:
Fom-2, Melon necrotic spot virus: nsv, Aphis gossypii: Vat),
and polygenic partial resistances (Cucumber Mosaic Virus, Watermelon
Mosaic Virus 2, Papaya Ringspot Virus-watermelon type, Squash
Mosaic Virus) has been crossed with Vidrantais which is susceptible
to the above diseases and resistant to race 0 and 2 of fusarium
wilt (Fom-1). These two genotypes differ too by their carpel
numbers; trimerous for Vidrantais and pentamerous for PI 161375.
This character is controlled by one allele (p : pentamerous).
Parents, F1 and F2 progenies (220
plants) have been studied for their isozymes polymorphisms,
RAPD and RFLP. A total number of 140 arbitrary 10-mer oligonucleotide
primers were screened for their ability to detect RAPD. On
average, 4 amplified products were detected per primer. Over
598 amplified products scored, 145 were polymorphic between
the two parental lines, which represents 24.2% of polymorphism.
To date, 29 primers have been used for studying 61 polymorphic
bands segregating in the F2 progenies. Of these
61 markers, 15 showed a segregation distortion in the F2:
8 markers favored alleles of Vedrantais and 7 favored alleles
of PI 161375. Four RAPD markers presented a codominant segregation.
A research of RFLP was undertaken using a cDNA library from
melon (Balagui 1993). Restriction fragment patterns of 727
probe-enzyme combinations (6 enzymes and 131 probes) were examined.
Restriction enzymes were classified according to their efficiency
in detecting polymorphism: EcoRV> EcoRI> HindIII> XbaI> BamHI> DraI.
150 probe-enzyme combinations (with 71 probes) detected 20.6%
of polymorphism between the two parental lines. A linkage map
was developed. Thirteen linkages groups (melon has 2n=2x=24
chromosomes) contained 53 RAPD, one isozyme (PGD), four monogenic
characters (Fom-1, Fom-2, nsv, p) and 13 RFLP. Eight RAPD,
one RFLP markers and Vat were unlinked. The ordering of the
markers in linkage group is not always possible because linkage
detection in F2 populations is highly inefficient
for dominant markers in repulsion phase (Allard 1956). It is
necessary to incorporate a higher number of codominant markers
to order them within the linkage groups.
#27 Preliminary Analysis of dsRNA Length Polymorphisms
in Clonal, Root, and Field Populations of Monosporascus
B. R. Lovic, V. A. Valadez, D. J. Lofland, R. D. Martyn,
and M. E. Miller, Department of Plant Pathology and Microbiology,
Texas A&M University, College Station 77843 and TAES, Weslaco
A hierarchical sampling strategy was employed in two 15-acre
muskmelon fields to collect isolates of Monosporascus cannonballus,
causal agent of root rot/vine decline of watermelon and muskmelon.
Isolations were performed by plating sections of surface-sterilized
roots on streptomycin-amended water agar. The number of isolates
obtained from any individual root system varied from 1 to 26.
The isolates were grown in liquid medium, nucleic acids were
extracted using a standard CTAB protocol, and dsRNA length
polymorphisms were visualized following gel electrophoresis
of total nucleic acid preparations on ethidium bromide-stained
gels. The fragments were identified as dsRNA by the resistance
to RNase in high-salt buffer and by a green fluorescence following
acridine-orange staining. Of the 300 isolates collected, 65%
harbored 1 to 13 dsRNA fragments that varied in length from
1.7 to 3.7 kb relative to a DNA size marker. The dsRNA pattern
in any individual isolate (clone) appeared to be stable in
subcultures. A total of 16 different patterns were observed
among isolates within the entire field. Up to eight different
patterns were observed among the dsRNA-containing isolates
sampled from a single root system. Analysis of the spatial
distribution of polymorphic types revealed no clustering in
either of the two fields examined.
#28 Vine Decline Problems Affecting Melons in California.
T.R. Gordon, R.M. Davis and J. Valencia; Department of Plant
Pathology, U.C. Berkeley, Department of Plant Pathology, U.C.
Davis, and U.C. Cooperative Extension, Modesto, CA.
Muskmelon (Cucumis melo L.) in the San Joaquin Valley
of California is commonly affected by decline problems which
manifest themselves shortly before fruit maturity. These problems
are seen on western shipping types, Honey Dew and Crenshaw
melons, among others. The extent of the decline varies but
often results in a complete collapse of the vines and a substantial
if not complete loss of yield. Vine collapse is more commonly
observed on late planted melons, those reaching maturity in
late summer and early fall. In general, plants which have collapsed
do not show conspicuous damage on their tap or primary lateral
roots. However, roots may have a somewhat corky appearance,
and small lesions are sometimes evident. Acremonium sp.
and Pyrenochaeta Sp. have been isolated from symptomatic
roots. Both of these fungi are being tested for their ability
to cause the decline syndrome under field conditions, the possible
involvement of Monosporascus cannonballus is also being
#29 Searching for Resistances to Sphaerotheca fuliginea and
Two Yellowing Diseases in Cucumis melo and Related Cucumis Species.
G6mez-Guillam6n, M.L., Tores, J.A., Soria, C., Sese, A.I.L. "La
Mayora" Experimental Station - C.S.I.C. 29750-Algarrobo, Malaga,
Since 1989, 324 accessions of Cucumis melo (233 were
Spanish accessions) and 15 of related Cucumis species
have been tested against Sphaerotheca fuliginea races
1 or 2 and two yellowing viruses transmitted, one by Trialeurodes
vaporariorum, the other by Bemisia tabaci. Accessions
were previously tested under natural conditions of infection
in the field and the symptomless accessions were then tested
against the respective pathogens in the laboratory. Six
C. me.70 accessions showed resistance against S. fuliginea race
1, ten were race 2 resistant, and one showed resistance to
both races 1 and 2. The tested accessions of C. africanus,
C. myriocarpus, C. anguria var. Iongipes, C. dipsaceus, and
C. metuliferus were also resistant to race 2. One accession
of C. myriocarpus, C. africanus, and C. metuliferus showed
resistance to the yellowing virus transmitted by T. vaporariorum. Only
one accession of C. melo was tolerant against that virus.
The C. metuliferus accession tested and one of C. melo showed
resistance to the yellowing virus transmitted by
#30 Field and Greenhouse Screens for Gummy Stem Blight
Resistance in Cucumis melo and Cucurbita spp.
Yiping Zhang, Konstantinos Anagnostou, Tom A. Zitter, and
M.M. Kyle, Departments of Plant Breeding and Plant Pathology,
Cornell University, Ithaca, NY 14853.
Greenhouse and field evaluations for resistance to gummy
stem blight, the foliar symptoms caused from infection by the
fungus Didymella bryoniae (Auersw.), were conducted
on 798 USDA Plant Introduction accessions of Cucumis melo and
200 Cucurbita accessions. Plants were inoculated at
3-4 true leaf stage with a severe isolate of D. bryoniae collected
from Onondaga County, NY, and disease indices were calculated
based on foliar necrotic lesions. In greenhouse screens and
two years of field screens, several melon PIs showed high levels
of resistance that at least equaled and often exceeded the
level of resistance observed in the leading source of resistance
to date, PI 140471: PI 157082, 157081, 157076, 255478, 482399,
432398, 482408 and 482393. PI 482399 which was intermediate
between an agrestis and dudaim type was more productive than
the other highly resistant accessions. Data analyses revealed
that screen results for a given accession in greenhouse and
field experiments were correlated with r-values from 0.731
to 0.916. Crosses have been made to transfer resistance into
market types and to determine the inheritance and relationships
among resistance sources. An accession of C. martinezii obtained
by Henry Munger from T.H. Whitaker and used at Cornell as a
source of resistance to cucumber mosaic virus and powdery mildew
resistance is the best source of resistance to foliar symptoms
we have located to date in the Cucurbita spp.
#31 Silverleaf Whitefly on Melons in California, Florida,
South Carolina and Texas.
James D. McCreight1, Gary W. Elmstrom2,
Alvin. M. Simmons3 and David W. Wolff4, 1USDA-ARS, U.S. Agricultural
Research Station, 1636 East Alisal Street Salinas, CA 93905; 2University
of Florida, Central Florida Research and Education Center,
5336 University Ave., Leesburg, FL 34748; 3USDA-ARS,
U.S. Vegetable Laboratory, 2875 Savannah Highway, Charleston,
SC 29414; 4Texas Agricultural Experiment Station,
Texas A&M University System, 2415 East Hwy. 83, Weslaco,
Silverleaf whitefly (Bemisia argentifolii Bellows & Perring)
is a serious pest of melon (Cucumis melo L.) in the
major production areas of the continental U.S. We compared
infestation levels and feeding effects of whitefly populations
at Brawley, Calif., Leesburg, Fla., Charleston, S.C. and Weslaco,
Texas. Mainstream, Perlita, Primo and Top Mark were planted
in a field at each location during mid-August using a randomized
complete- block design with cultivars as whole plots and insecticide
treatments (control no insecticide, insecticide treated) as
subplots in four replications. Each whole plot consisted of
six hills spaced 76 cm apart (30 inch) within rows; rows were
on 203 cm (80 inch) centers. Five seeds were planted per hill;
seedlings were thinned to two per hill at the first leaf stage
of growth. Bifenthrin insecticide (Capture) at 0.36 g a.i.
ha-1 (0.08 lb a.i. acre-1) was applied
once each week and Endosulfan insecticide (Thiodan) at 45 g
a.i. ha-1 (1.0 lb a.i. acre-1) was
applied in combination with Bifenthrin one, three and five
weeks post- planting. Adult whiteflies were counted on the
third leaf from the terminal bud of the main vine each week
through eight weeks post-planting. At four and eight weeks
post-planting the following data were also recorded: main vine
length, plant condition (1 to 9 scale), number of fruit, vine
fresh and dry weights, numbers of eggs and nymphs on the third
leaf from the terminal bud of the main vine, and area of the
third leaf. Infestation levels varied
#32 Plant Population Studies Utilizing Six Plant Spacings
and Three Honeydew Melon Cultivars.
L.P. Brandenberger*, R.P. Wiedenfeld and M. Perches, Texas
Agricultural Extension Service and Experiment Station, 2401
East Hwy. 83 Weslaco TX 78596.
The study repeated in 1994 included three cultivars; 'Honeybrew',
'Morning Ice' and 'Sure 7050' combined with spacing treatments
including; single row 8", single row 10", single row 12", double
row 8", double row 12" and double row 24". All spacing-cultivar
treatments were planted in a randomized design utilizing five
replications on top of raised beds on 80" centers in a commercial
field on February 14, 1994 by direct seeding 4-5 seeds for
each spacing interval . Prior to planting, raised beds were
covered with black plastic mulch and drip irrigation installed.
After emergence, the honeydew seedlings were thinned to one
plant per spacing interval on March 8. Plots were harvested
by commercial harvesting crews on May 20, 27, 31 and June 8.
Results indicate that different plant spacings and honeydew
cultivars can influence yields of different size fruit, earliness
and returns/acre over different seasons and environments although
they acted independent of one another. The lower plant populations
i.e. single row 10", single row 12" and double row 24" spacings
resulted in the production of greater numbers of larger fruit.
The higher plant populations i.e. single row 8", double row
8" and double row 12" spacings resulted in the production of
greater numbers of smaller fruit. Sure 7050 produced significantly
more size 4 and 5 melons than either Morning Ice or Honeybrew,
while Honeybrew produced significantly more size 8, 9 and 10
melons. Morning Ice produced the most size 6 melons. In both
the 1993 and 1994 studies, the double row 24" spacing resulted
in an earlier harvest evidenced by a higher percent harvest
for the first harvest on both years. Sure 7050 was significantly
later than either Honeybrew or Morning Ice. Returns/acre were
significantly different for the spacing treatments for three
out of four harvest dates. The double row 24" spacing resulted
in the highest returns/acre and was significantly higher than
three of the other spacings on May 20. Both Morning Ice and
Sure7050 had significantly higher returns when compared to
Honeybrew even though total yields for each cultivar were not
significantly different. There was a significant difference
between spacing treatments for percent soluble solids for the
May 31 harvest, but it would be difficult to determine without
additional studies if this difference could be repeated between
seasons and locations. Sure 7050 resulted in significantly
lower percent soluble solids than Morning Ice for three of
the four harvests.
#33 Comparison of Genetic Control to Chemical Control
and Evaluation of an Integrated Program for Managing Powdery
Mildew in Summer Squash.
Margaret Tuttle McGrath, Department of Plant Pathology, Long
Island Horticultural Research Laboratory, Cornell University,
Riverhead, NY 11901-1098.
Field experiments were conducted between 1991 and 1994 to
evaluate powdery mildew resistant (PMR) summer squash (Cucurbita
pepo), IPM chemical control programs (fungicides applied
after disease detection), and programs combining integrated
use of genetic and chemical control during late summer when
powdery mildew pressure is greatest. PMR PSX 2287, HMX 1707,
and Park's Crookneck (released in 1994) were compared with
the susceptible cultivars Goldbar, Supersett, and Park's Creamy,
respectively. The fungicide chlorothalonil (7-day interval)
was applied with either triadimefon (14-day) or benomyl (14-day)
in 1991-1993 and with triadimefon (14-day) in 1994. Similar
disease suppression was obtained with an IPM program (2-5 sprays)
as with a preventive schedule (5-8 sprays). Applying fungicides
to PMR plants resulted in improved control with the experimental
lines in 1991-1993 but not with Park's Crookneck in 1994; however,
only PSX 2287 produced significantly more fruit during the
last third of the harvest period when treated with fungicides.
For example, 57 days after transplanting, average severities
on adaxial/abaxial leaf surfaces were 3%/14% and 0%/0.1% for
nontreated and fungicide-treated HMX 1707 in 1993, respectively,
and 1.8%/1.3% and 1.9%/0% for nontreated and fungicide- treated
Park's Crookneck in 1994. Powdery mildew was not suppressed
adequately with fungicides on abaxial leaf surfaces of susceptible
cultivars in 1993 and 1994, most likely because of resistance.
Average severities were 26%/52% and 0%/49% for nontreated and
fungicide-treated Supersett. All isolates tested at the end
of the epidemic in 1993 were insensitive to triadimefon and
benomyl. The fungicide-treated susceptible cultivars produced
more fruit than the nontreated PMR cultivars in all experiments;
however, genetic control was more economical than chemical
#34 The Dominant Wf (White Flesh) Allele is
Necessary for Expression of "White" Mature Fruit Color in Cucurbita
Harry S. Paris, Dept. of Vegetable Crops, A.R.0., Newe Ya'ar
Research Center, P. O. Box 90000, Haffa 31-900, Israel.
White Bush Scallop, a cultivar having "white" (very pale
yellow green) mature fruits and white fruit flesh, was crossed
with Vegetable Spaghetti, a cultivar having light yellow mature
fruits and yellow flesh, and Jack O'Lantern, a cultivar having
dark orange mature fruits and orange flesh. Filial and backcross
progenies were observed and scored for mature fruit color and
flesh color. The results suggested that the W ("white
fruit") allele is responsible for lack of green coloration
(chlorophyll pigmentation) on the fruit exterior but has less
effect on yellow and orange coloration (carotenoid pigmentation)
and little or no visible effect on the fruit flesh. The results
confirmed that the Wf allele, which confers white
fruit flesh color, is dominant to wf, which confers colored
fruit flesh. In the cross with Vegetable Spaghetti, white mature
fruits were produced only when both W and Wf were
present. Therefore, colored flesh (wf/wf)
is epistatic to white (W/-) fruit. Results from
filial and backcross generations of the cross with Jack O'Lantern
indicate that the white fruit color is recessive to orange
fruit color and hypostatic to wf: W/- wf/wf fruits
range from light yellow to intense yellow in color. Therefore,
the gene for white fruit should be symbolized by lower case w and
not upper case W. Or, as I hereby suggest, that
the gene name be changed from "white fruit" to "weak chlorophyll
pigmentation", permitting retention of the present symbol, W,
and thereby preventing possible future confusion in the literature.
Texas Subtropical Agricultural Center /
Texas A&M University / Weslaco, Tx 78596-8399 /
Last modified: Thursday June 1 1995 by MRG