Variable Resistance to Gummy Stem Blight in Watermelon PI 271778

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  • 1 Department of Horticulture and Department of Plant Pathology, The University of Georgia Coastal Plain Experiment Station, College of Agricultural and Environmental Sciences, Tifton Campus, Tifton, GA 31793-0748

Seeds from 19 selfed plants of watermelon PI 271778 were field-planted with seven cultivars in July 1997. Two weeks after planting, one seedling per plot was inoculated on 15 July by spraying to runoff (24 × 104 conidia/mL in water) a mixture of indigenous isolates of Didymella bryoniae. Plants were inoculated again on 31 July. On 7 Aug., plants with at least one stem lesion ranged from 0% to 96% (mean = 22%) for selections from PI 271778, while cultivars ranged from 3% to 71% (mean = 24%). On 19 Aug., plants with at least one stem lesion ranged from 12% to 100% (mean = 74%) for selections and 94% to 100% (mean = 97%) for cultivars. These differences were further reflected in average dead canopy of 25% for selections and 80% for cultivars on 3 Sept. By 17 Sept., dead canopy averaged 47% for selections and 100% for cultivars. Fruit harvested per plant averaged 2.5 for selections and 0.8 for cultivars. By harvest, vines were totally collapsed on all cultivars and on some selections, while stems of most selections were still vigorous but leaves exhibited significant necrosis.

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