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Developing and
enhancing the
genetics of economically-important
cucurbits

Cucurbitaceae 94: Evaluation and Enchancement of Cucurbit Germplasm

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 Fruit.

Perry E. Nugent, USDA-ARS, U. S. Vegetable Laboratory, Charleston, SC, 29414.

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 process.

#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 (PIs).

#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 present.

#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 patterns.

#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, 46526.

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 orbiculare.

L.A. Wasilwa, J.C. Correll, and T.E. Morelock, Depts. of Plant Pathology and Horticulture, University of Arkansas, Fayetteville, AR 72701.

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 tests.

#13 Screening the Cucumber Germplasm Collection for Nine Horticultural Traits.

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 in Cucumber.

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, MI 48824.

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 reductions.

#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 in 1994.

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, TX 78596

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 Content.

Gene Lester, USDA-ARS and Frank Eischen, Texas A&M, Weslaco, TX 78596.

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 Kless (2),

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 Perl-Treves

Department of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel.

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 morphological traits.

#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 cannonballus.

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 78596.

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 considered.

#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, Spain.

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 B. tabaci.

#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, TX 78596-8399

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 control.

#34 The Dominant Wf (White Flesh) Allele is Necessary for Expression of "White" Mature Fruit Color in Cucurbita pepo.

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

 

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