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Jennifer Tillman, Ajay Nair, Mark Gleason, and Jean Batzer

Current cucurbit production systems in the United States often rely on tillage and plastic film mulches to create favorable growing conditions of warm soils and minimal weed pressure around plants; however, there are environmental concerns about the

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Chieri Kubota, Michael A. McClure, Nancy Kokalis-Burelle, Michael G. Bausher, and Erin N. Rosskopf

alternative rootstocks available would help develop long-term strategies for pest and disease control, particularly for introduction of grafting into open-field tomato production. Grafted cucurbit seedling production and use. Several commercial trials

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Joyce G. Latimer and Reuben B. Beverly

Brushing (40 strokes per 1.5 minutes, twice daily) or moisture stress conditioning (MSC) (daily nonlethal dry-down cycles) reduced seedling growth of two cucumber (Cucumis sativus L.) cultivars in 1991 and three squash (Cucurbita pepo L.) cultivars in 1991 and 1992. In both years, watermelon [Citrullus lanatus Thunb. (Matsum. & Nakai)] cultivars varied in responsiveness to brushing; brushing reduced stem length 0% to 44% over four cultivars in 1992. MSC reduced growth of all cultivars. Brushing increased the rate of water loss from detached leaves of cucumber, squash, and watermelon, whereas MSC decreased water loss from leaves of cucumber and squash. In 1991, under well-watered posttransplant conditions, MSC increased the mean relative growth rate (RGR) of cucumber and watermelon transplants in the greenhouse. Brushing increased the RGR of watermelon transplants. In 1992, MSC increased the RGR of squash and watermelon transplants grown under posttransplant drought-stressed conditions, while brushing had no effect. Both conditioning treatments controlled plant growth in the greenhouse without diminishing subsequent plant performance.

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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted in 1993, 1994, and 1996 to determine the tolerance of several cultivars of zucchini and yellow crookneck squash (Cucurbita pepo L.) to various rates and methods of application of clomazone, ethalfluralin, and pendimethalin. Applying herbicides preplant soil incorporated (PPI), preemergence (PRE), at seedling emergence (SE), or early postemergence (EPOT) resulted in plant injury that varied from 0% to 98%. Ethalfluralin and pendimethalin (PPI) at 1.12 kg·ha–1 a.i. resulted in the greatest stand and yield reductions across all cultivars. Fruit number and weight declined for all cultivars in 1993 and 1994 as the amount of pendimethalin applied PRE was increased. Zucchini (`Senator') fruit size was significantly reduced for the first three harvests in 1993 by PRE application of pendimethalin or PPI application of ethalfluralin, at all rates. Yellow squash (`Dixie') fruit size was unaffected by herbicide treatment for any harvests during 1993 or 1996. Yellow and zucchini squash yield, fruit number, and average fruit weight were equal to, or greater than, those of the untreated control for PRE clomazone using either the emulsifiable concentrate formulation (EC) during 1993, 1994, and 1996 or the microencapsulated formulation (ME) during 1996. Foliar bleaching and stunting by clomazone was evident in early-season visual observations and ratings, but the effect was transient. Foliar bleaching by clomazone PPI (1.12 kg·ha–1 a.i.) was more evident in `Senator' zucchini, and yield was significantly reduced in 1993. These effects of clomazone PPI were not evident in 1994 for either `Elite' or `Senator' zucchini squash. Chemical names used: 2-[(2-chlorophenyl)methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone); N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl) benzenamine (ethalfluralin); N-(1-ethylopropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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James D. McCreight and Albert N. Kishaba

Squash leaf curl (SLC) is a virus disease of squash transmitted by the sweetpotato whitefly [Bernisia tabaci (Germ.)]. 'Cucurbita maxima Duch. ex Lam., C. mixta Pang, and C. pepo L. cultivars and the wild taxon. C. texana Gray exhibited severe symptoms in response to SLC in greenhouse and field tests. Symptoms on C. moschata (Duch.) Duch. ex Poir. cultivars were much more severe in greenhouse tests than in field tests. Three wild species, C. ecuadorensis Cutler and Whitaker, C. lundelliana Bailey, and C. martinezii Bailey, were virtually immune in greenhouse tests, but were infected in field tests. Cucurbita foetidissima HBK expressed moderate symptoms in a field test. Benincasa hispida (Thunb.) Cogn., C. ficifolia Bouche, Lagenaria siceraria (Mol.) Standl., Luffa acutangula (L.) Roxb., Luffs aegyptiaca Mill., and Luffs graveolens Roxb. were resistant to SLC in greenhouse and field tests.

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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted in 1993, 1994, and 1995 to determine tolerance of seeded and transplanted watermelon [Citrullus lanatus (Thunb.) Matsum and Nak.] to clomazone, ethalfluralin, and pendimethalin using method of stand establishment (directseeded vs. transplanted) and time of herbicide application [preplant soil incorporated (PPI), preplant to the surface (PP), or postplant to the surface (POP)] as variables. Yield and average fruit weight in plots with clomazone were equal to or greater than those in control plots for the 3-year study regardless of method of application. Bleaching and stunting were evident with clomazone in early-season ratings, but injury was transient and did not affect quality or yield. Of the three herbicides, ethalfluralin PPI resulted in the greatest injury, stand reduction, and yield reduction of the three herbicides. Pendimethalin (PPI, PP, or POP) reduced yield of direct-seeded but not of transplanted watermelon. Chemical names used: 2-[(-2-chlorophenyl)methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone); N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl) benzenamine (ethalfluralin); N-(1-ethylopropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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Raymond L. Clark, Mark P. Widrlechner, Kathleen R. Reitsma, and Charles C. Block

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Todd C. Wehner, Rachel P. Naegele, and Penelope Perkins-Veazie

Citrulline, arginine, and lycopene are naturally occurring compounds found in watermelon, Citrullus lanatus (Thumb) Matsum & Nakai, with beneficial effects on plant growth and human health. This study evaluated seven commercial cultivars and one breeding line for citrulline, arginine, and lycopene content in mature fruit grown at two locations in North Carolina. Correlations among these compounds and fruit quality traits (percent soluble solids and flesh pH) were evaluated. Watermelon cultigens evaluated were chosen for their fruit trait diversity. ‘Yellow Doll’ and NC-517 possessed the highest citrulline and combined concentration of citrulline and arginine of all cultigens evaluated. Lycopene content was highest in ‘Dixielee’, followed by ‘Sugar Baby’, and ‘Allsweet’, each of which have different shades of red flesh color. Location and its interaction with genotype had no significant effect on arginine or lycopene concentration. Broad-sense heritability was estimated for each trait. Arginine content (89%) and lycopene content (99%) had very high heritability. Citrulline content (41%), percent soluble solids (46%), and flesh pH (61%) had moderate heritability. Lycopene was positively correlated with flesh pH (r = 0.517) and negatively correlated with percent soluble solids (r = −0.344). Arginine content had a weak negative correlation with flesh pH (r = −0.343) and was not correlated with percent soluble solids.

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Charlie G. Summers, Jeffrey P. Mitchell*, and James J. Stapleton

Trials were conducted in 2002 and 2003 in California's San Joaquin Valley to determine the efficiency of reflective plastic and wheat straw in managing silverleaf whitefly and aphid-borne virus diseases in late planted cantaloupes. In 2002, the incidence of aphid-borne viruses was lowest in plants growing over reflective plastic followed by those growing over wheat straw and then those growing over bare soil. Wheat straw mulch was as effective as reflective plastic during the early part of the growing season in reducing the incidence of virus disease, but by mid-season, the reflective plastic was superior. The incidence of virus diseases in plants growing over wheat straw was significantly (P < 0.05) lower than that in plants growing over bare soil throughout the season. Whitefly numbers (nymphs per cm2) and aphid numbers were significantly reduced on plants growing over both reflective mulch and wheat straw mulch compared to those growing over bare soil. Yields of all sizes of melons were significantly higher in the reflective mulch plots and yield for the straw mulched and bare soil plots were not significantly different. Results in 2003 were similar to those of 2002. Both whitefly numbers and aphid numbers were significantly lower in plants growing over both mulches than in those growing over bare soil. Virus incidence was initially low but following an aphid flight in late August, the number of infected plants increased rapidly. Both the reflective plastic and straw provided equal protection form aphid-borne viruses throughout the growing season. Yields were highest in the reflective plastic plots, followed by the straw mulch and finally the bare soil. Differences were significant (P < 0.05) among all three treatments.

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Hae-Jeen Bang, Soo-Jung Hwang, Hyun-Sook Ham, and Jung-Myung Lee

Dry heat treatment has been commonly used to inactivate some seed-borne pathogens in vegetable seeds. Virtually all the gourd seeds for watermelon rootstock are being treated with dry heat to inactivate cucumber green mottle mosaic virus (CGMMV, a strain of tobamovirus) and Fusarium. Seeds of five gourd and one squash cultivars were treated with dry heat (35 °C for 24 h + 50 °C for 24 h + 75 °C for 72 h) and, immediately after the dry heat treatment, the seeds (moisture content of 1% or lower) were allowed to absorb atmospheric moisture in a moisture saturated chamber until the seed moisture contents reached 2% to 8%. After the equilibrium obtained, the seeds were sealed in air-tight bags and stored for 1 day or 30 days at 20 °C. The seeds were then sown in cell trays and the emergence and seedling characteristics were evaluated. Dry heat treatment caused significant delay in emergence in all tested cultivars, but had little or no influence on the final emergence rate. Moderate to severe injury was observed in seedlings grown from dry heat-treated seeds in three out of six cultivars tested. However, little or no dry heat phytotoxicity was observed in other cultivars, thus suggesting the marked differences in cultivar susceptibility to dry heat treatment. Rapid humidification before sealing also appeared to reduce the early emergence rate in some cultivars, but had no effect on the final emergence rate in most cultivars. Storage of dry heat-treated seeds in sealed bags for 30 days before sowing was highly effective in minimizing the phytotoxicity symptoms in seedlings as compared to the seedlings grown from the seeds sown immediately after the dry heat treatment. This suggests that the reestablishment of metabolic process required for normal seed germination requires a long period after the dry heat treatment. Other characteristics associated with DH treatment will also be presented.