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George H. Clough and Philip B. Hamm

Three transgenic yellow crookneck squash (Cucurbita pepo var. melopepo) and five transgenic cantaloupe (Cucumis melo, Reticulatus group) lines were field-tested in 1993 and 1994, respectively, for resistance to Zucchini Yellow Mosaic Virus and Watermelon Mosaic Virus II. During both years, non-transgenic plants were inoculated with virus before transplanting to provide a high virus threat to the transgenic plants. Before and after transplanting, serological (ELISA) testing was used to obtain baseline information on transformed plants and to confirm field virus infection. In both years, plant disease development was rated weekly; yield was assessed during 1993. Disease progression, yield, and end-of-season ELISA indicated a significant reduction in frequency of disease incidence in the transgenic lines. Total squash yields did not differ between the transformed and unchanged lines, but the transgenic lines yielded more marketable fruit than the non-transgenic line.

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Stephen Reiners and Dale I.M. Riggs

Field studies were conducted at two locations in 1995 to determine the effect of spacing, nitrogen application, and variety on pumpkin (Cucurbita pepo L.) marketable yield. Pumpkin yield was unaffected by three rates of applied N (67, 112, or 157 kg N·ha-1). Marketable fruit number per hectare increased with both 'Howden' and 'Wizard' pumpkins as in-row plant spacing decreased from 1.2 to 0.3 m. Average fruit size significantly decreased at the closer spacing, but the decline in mass was much greater in nonirrigated as compared to irrigated plots. This resulted in a significantly greater yield in the irrigated plots at the closer spacing, while there was no significant increase in yield without irrigation. The results demonstrate that growers may increase the number of fruit per unit area with closer spacing but optimal soil moisture may be a prerequisite for the increase.

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D.S. NeSmith

Greenhouse and field experiments were conducted to determine the influence of transplant age on growth and yield of `Dixie' and `Senator' summer squash (Cucurbita pepo L.). Dry weight and leaf area measurements indicated that 28- to 35-day-old greenhouse-grown transplants grew more slowly after transplanting than plants that were 10, 14, or 21 days old. Older transplants flowered earlier; however, earlier flowering did not result in higher early yields. Transplants of varying ages did not differ greatly in yield and yield components in the field, although all transplants had higher early yields than the directly seeded controls. Results from these experiments suggest that 21 days may be a reasonable target age for transplanting summer squash. If transplanting were delayed by adverse planting conditions, 21-day-old transplants would likely have at least a 10-day window of flexibility before yields would be reduced notably by additional aging.

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Willie O. Chance III and Harry A. Mills

Mature zucchini squash plants (Cucurbita pepo L.) were grown under four NO3:NH4 ratios (1:0, 3:1, 1:1, and 1:3) to determine effects on macronutrient nutrition. Plants were grown in solution culture under greenhouse conditions. Treatments were applied at first bloom. Highest uptake of Ca and Mg occurred in the 1:0 NO3:NH4 treatment while higher K uptake was found in the 3:1 NO3:NH4 treatment. Total nitrogen uptake was greatest in the 1:1 and 3:1 NO3:NH4 treatments. A 3:1 NO3:NH4 ratio applied at first bloom gave best overall uptake of N, K, Ca, and Mg.

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Willie O. Chance III and Harry A. Mills

Mature zucchini squash plants (Cucurbita pepo L.) were grown under four NO3:NH4 ratios (1:0, 3:1, 1:1, and 1:3) to determine effects on macronutrient nutrition. Plants were grown in solution culture under greenhouse conditions. Treatments were applied at first bloom. Highest uptake of Ca and Mg occurred in the 1:0 NO3:NH4 treatment while higher K uptake was found in the 3:1 NO3:NH4 treatment. Total nitrogen uptake was greatest in the 1:1 and 3:1 NO3:NH4 treatments. A 3:1 NO3:NH4 ratio applied at first bloom gave best overall uptake of N, K, Ca, and Mg.

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Paula P. Chee

Plant regeneration from tissue cultures of summer squash (Cucurbita pepo L. ev. YC60) has been observed. Embryogenic callus tissues were initiated when cotyledons of mature seeds were excised and cultured on Murashige and Skoog (MS) medium supplemented with either 22.7 μm 2,4-D or a combination of 4.7 μm 2,4,5-T, 4 μm BA, and 0.5 μm kinetin. Clusters of somatic embryos were found in callus tissue. Maturation of these somatic embryos was effected by transfer of embryogenic callus tissues to MS supplemented with 0.5 μm NAA and 0.25 μm kinetin. Regenerated mature plants were morphologically normal and set fruits containing seeds that germinated normally. Chemical names used: 6-benzylaminopurine (BA); 2,4-dichlorophenoxyacetic acid (2,4-D); α - napthaleneacetic acid (NAA); 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).

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Owusu A. Bandele, Marion Javius, Byron Belvitt and Oscar Udoh

Fall-planted cover crops of hairy vetch (Vicia villosa Roth), Austrian winter pea (Pisum sativum subsp. arvense L. Poir), and crimson clover (Trifolium incarnatum L.) were each followed by spring-planted 'Sundance' summer squash [Cucurbita pepo var. melopepo (L.) Alef.] and 'Dasher' cucumber (Cucumis sativus L.). Squash and cucumber crops were followed by fall 'Florida Broadleaf mustard green [Brassica juncea (L.) Czerniak] and 'Vates' collard (Brassica oleracea L. Acephala group), respectively. The same vegetable sequences were also planted without benefit of cover crop. Three nitrogen (N) rates were applied to each vegetable crop. Squash following winter pea and crimson clover produced greater yields than did squash planted without preceding cover crop. Cucumber following crimson clover produced the greatest yields. No cover crop effect was noted with mustard or collard. Elimination of N fertilizer resulted in reduced yields for all crops, but yields of crops with one-half the recommended N applied were generally comparable to those receiving the full recommended rate.

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Charles A. Powell, Peter J. Stoffella and Harry S. Paris

Zucchini squash (Cucurbita pepo L.) fruit yield and the incidence of sweetpotato whitefly (SPWF) [Bemisia tabaci (Gennadius)], squash silver leaf (SSL) disorder, and zucchini yellow mosaic virus (ZYMV) were measured during Spring and Fall 1991 in experiments containing various plant populations. In both experiments, as the within-row spacing increased from 30.5 to 76.2 cm or the number of plants per hill decreased from three to one, the number of marketable fruit per hectare decreased, and the marketable fruit per plant increased. Adult SPWF populations increased with decreased within-row spacing in the spring but not the fall experiment. The incidence of SSL or ZYMV infection was not affected by plant population in either experiment. The results indicate that increasing zucchini squash plant population can increase yield without affecting the incidence of SSL or ZYMV.

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James E. Brown, James M. Dangler, Floyd M. Woods, Ken M. Tilt, Michael D. Henshaw, Wallace A. Griffey and Mark S. West

Silver reflective plastic mulches were compared with conventional bare-ground culture of yellow crookneck summer squash (Cucurbita pepo L. var. melopepo Alef.) for reducing aphids and the following mosaic virus diseases: cucumber mosaic, watermelon mosaic I and II, zucchini yellows mosaic, and squash mosaic. Plants grown on silver plastic mulch produced higher marketable yields than those grown on bare ground. Other colors (white, yellow, and black with yellow edges) of plastic mulch were intermediate in their effects on aphid population and virus disease reduction. Silver reflective mulch alone and silver reflective mulch with insecticide were superior to other colors of plastic mulch in reducing aphid populations. Silver reflective plastic mulch, with or without insecticide, resulted in 10 to 13 days delay in the onset of the mosaic diseases noted.

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Jeffrey Anderson

Epiphytic populations of ice nucleation active (INA) bacteria responded differently to preconditioning temperature treatments depending on plant species. Ice nucleation activity of inoculated tomato (Lycopersicon esculentum Mill.), squash (Cucurbita pepo L.), and cucumber (Cucumis sativus L.) seedlings was not affected by preconditioning temperature treatments of 7, 21, or 33C for 3 hr prior to freezing assays. In contrast, preconditioning at 33C for 3 hr prior to assay decreased mean freezing temperatures of inoculated pine shoots compared with preconditioning at 5C. Preconditioning treatments of pine shoots had a greater effect on freezing temperatures when tissues were submerged in water during treatment. Cucumber seedlings responded similarly regardless of whether they were exposed to preconditioning treatments with dry surfaces or in a saturated environment. Preconditioning temperatures had a greater effect on ice nucleation activity of bacterial suspensions than on plants harboring INA bacteria.