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Disease Note. First Report of Watermelon Fruit Blotch in Delaware. T. A. Evans, Department of Plant and Soil Sciences, University of Delaware, Newark 19717-1303. R. P. Mulrooney, Department of Plant and Soil Sciences, University of Delaware, Newark 19717-1303. Plant Dis. 75:1074. Accepted for publication 8 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1074C. Watermelon fruit blotch, characterized by dark green, greasy, watersoaked
spots that rapidly expand on the upper side of mature watermelon
fruit, occurred in two fields in Sussex County in 1989. The
causal bacterium, which was easily isolated on nutrient broth-yeast
extract agar from the inner rind directly below and at the margins
of the fruit spot, was determined to have a fatty acid profile similar
to that of Pseudomonas pseudoalcaligenes subsp. citrulli Schaad et
al. Pathogenicity was confirmed when stems of cucumber (Cucumis
salivus L. 'National Pickling') and watermelon (Citrullus lanatus
(Thunb.) Matsum. & Nakai 'Charleston Grey,) were inoculated at
the first-true-Ieaf stage with 0.1 ml of suspensions containing either
106 or 108 cfu per milliliter and incubated in a moist chamber overnight. Water-soaked lesions appeared on the stems within 3 days, extended
to cotyledons and true leaves, and often led to collapse of the whole
stem within 5 days. Control seedlings injected with sterile saline
remained healthy. A bacterium with the same fatty acid profile was
reisolated from diseased plants. |