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Wilfredo Seda-Martínez, Linda Wessel-Beaver, Angela Linares-Ramírez, and Jose Carlos V. Rodrigues

showed 69% of all samples infected by ZYMV and 59% of samples infected with PRSV ( Paz-Carrasco and Wessel-Beaver, 2002 ). Infection with PRSV and ZYMV appeared to lower yields, especially in summer squash ( Cucurbita pepo L.) and tropical pumpkin

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Camille E. Esmel, Bielinski M. Santos, and James P. Gilreath

Nitrogen (N) is the most growth-limiting for vegetable production in sandy soils. In Florida, current recommendations for preplanting N applications (100 lb/acre of N) in `Crookneck' summer squash (Cucurbita pepo) differ from those used by the growers (>200 lb/acre). Therefore, two field studies were conducted in Ruskin and Balm, Fla., to examine the effect of 50, 100, 150, 200, 250, and 300 lb/acre of N on summer squash growth and yield. Variables collected during this study were plant vigor (0–10 scale, where 0 = dead plant) at 3 and 7 weeks after planting (WAP), petiole sap nitrate-nitrogen (NO3-N) at 4 and 8 WAS, and marketable yield starting on 4 WAS (13 and 10 harvests in Ruskin and Balm, respectively). In Ruskin, plant vigor increased linearly with N rates, whereas there was no significant N effect in Balm. No differences in petiole sap NO3-N were observed in either location. In Ruskin, there was a rapid marketable yield increase (§25%) between 50 and 100 lb/acre of N, followed by no change afterwards. In contrast, there was no yield response in Balm. In the latter location, no crop had been established in the previous 3 years, enabling the soil to maximize its organic N accumulation (>40 lb/acre organic-N), whereas in Ruskin the experimental location had been continuously planted during the last three seasons (§25 lb/acre organic-N). The data demonstrated that organic N is an important source of the nutrient to complement preplant applications in summer squash.

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James W. Shrefler, Warren Roberts, Charles Webber, Jonathan Edelson, and Merritt Taylor

Commercial organic vegetable production requires using soil improvement practices and effective weed control measures. Rye (Secale cereale) cover crops are known to suppress annual weeds. Research was begun in 2004 to measure crop yield, annual weed infestation, and weed control requirements for vegetable planting systems that begin with a rye cover crop. Poultry litter was used to supply nutrients and was applied based on a soil test and commercial vegetable recommendations. Rye `Elbon' was seeded 21 Oct. 2004 on beds with 1.8-m centers. Zucchini squash (Cucurbita pepo) `Revenue' was planted the following year using three crop establishment dates, such that transplanting occurred on 6 May, 3 June, and 29 June. Planting system treatments included: conventional tillage (CT), CT and plastic mulch (P), CT with stale seedbed, mow, mow and burn-down, mow and shallow till (ST), ST and burn-down. Following field preparation, squash was transplanted in a single row at the bed center with 0.77-m plant spacing. Drip irrigation was used in all plantings. Emerging weeds were removed by hoeing. Squash was harvested from each planting over approximately 3 weeks and total marketable fruit counts were determined. Marketable yields with P were approximately double those of the CT and ST treatments in the 6 May transplanting. Yields were comparable for CT and ST in the 3 June transplanting, but were significantly lower for the P treatment. There were no significant differences among the treatments that received tillage in the 29 June planting. However, the non-tilled treatments had significantly lower yields compared to tilled treatments.

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Dermot P. Coyne, James M. Reiser, Durward Smith, Lisa Sutton, Aly M. Ibrahim, and Dale Lindgren

Published as Paper No. 12638, Journal Series, Nebraska Agricultural Research Division. Research was conducted under former Project 20-14. The photograph of `Butterbowl' squash (Fig. 1) was provided by the W. Atlee Burpee and Co., 300 Park

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

`Striato d'Italia' (cocozelle group) and `Clarita' (vegetable marrow group) summer squash were grown in the greenhouse and field in the presence of sweetpotato whiteflies (Bemisia tabaci Germ.) and their susceptibility to leaf silvering was compared. Silvering was less severe in `Striato d'Italia' in the greenhouse and field.

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Rebecca Nelson Brown and James R. Myers

Marker-based selection for resistance to zucchini yellow mosaic virus in squash (Cucurbita spp.) would allow breeders to screen individual plants for resistance to multiple viruses. The C. moschata landrace Nigerian Local is widely used as a source of resistance in C. pepo breeding programs. We used RAPDs and bulk-segregant analysis to screen two BC1 populations for a marker linked to the dominant major gene for resistance from Nigerian Local. The initial cross was Waltham Butternut × Nigerian Local; the test populations were created from reciprocal backcrosses to Waltham Butternut. Both populations segregated 1:1 for resistance when hand-inoculated with ZYMV. RAPD primers were screened on a resistant bulk and a susceptible bulk from each population, and Waltham Butternut and Nigerian Local. Primers that gave bands linked to resistance were further screened using DNA from individual plants in each population. The potential markers will be tested on several populations derived from crosses between summer squash (C. pepo) and Nigerian Local to determine if they would be useful for selection in a C. pepo background.

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D. Scott NeSmith

Research over a two year period assessed the influence of planting date and location on time to flowering and number of flowers produced for five summer squash (Cucurbita pepo L.) cultivars. Heat units (HU) were calculated using a single equation to determine if this approach could account for a significant portion of the variability in time to onset of flowering over the range of environments. Depending on cultivar and flower sex, the number of days to flowering varied as much as 20 days. There were significant cultivar differences in HU required for the onset of both staminate and pistillate flowers. The use of HU instead of days reduced the variability of time to flowering as indicated by regression analyses and mean absolute differences between predicted and observed days to flowering. The total number of staminate flowers produced was more variable than that of pistillate flowers. The ratio of pistillate-to-staminate flowers was stable for two of the five cultivars; however, pistillate flower production for those two cultivars was severely restricted during hot weather. Thus environment has a considerable influence on both the onset of flowering and the number of flowers produced for summer squash.

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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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James E. Ells, E. Gordon Kruse, and Ann E. McSay

Roots of acorn squash were washed from soil cores, dried and weighed. The cores were taken in a pattern about individual plants to reflect the roots present in each selected zone at different periods during the season. A different plant was sampled at each period so that there would be no effect from previous sampling. The root weights were multiplied by factors commensurate with the volume of soil represented by each core sample. Two years data have indicated that irrigation level effects the size of the root system but not its distribution. Density of roots was always greatest in the top 15 cm of soil and this zone of the greatest density progressively moved out from the center of the plant with time. Pattern of root distribution was not effected by plastic mulch, bare ground, trickle or furrow irrigation treatments. Root distribution was the same on all sides of the plant.

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Sergio Garza Ortega and Andres Tacho Amaya

The Gray Zucchini cultivar of summer squash is widely consumed as a fresh market vegetable in Northwest Mexico but is highly suceptible to viral diseases. Gray Zucchini type lines were developed by interspecific hybridization using a local landrace of Cucurbita moschata, which has shown high levels of viral resistance, as male parent and suceptible C. pepo cv. classic as female. The lines were obtained after 4 backcrossing and 3-5 selfing generations. In 1993 average commercial yield of first generation hybrids between lines was 28,155 kg/ha followed by line × Gray Zucchini hybrids, lines, commercial hybrids (Classic. Corsair, Onyx, Raven), and open pollinated cultivars (Gray Zucchini, Black Zucchini) with 26,594, 21,062, 18,862 and 10,172 kg/ha respectively. Yield was inversely related to symptoms of viral infection.