First Report of Bacterial Fruit Blotch of Watermelon in Oklahoma. J. L. Jacobs, Department of Plant Pathology, Oklahoma State University, Stillwater 74078-9947. J. P. Damicone, and B. D. McCraw. Department of Plant Pathology, and Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater 74078-9947. Plant Dis. 76:1185. Accepted for publication 28 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1185D.
Mature watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai
'Jubilee') from a field in Carter County, Oklahoma, in 1991 had large,
irregular, olive green, water-soaked areas on the upper side of the
fruit. Estimated yield losses in marketable fruit ranged from 10 to
15% in this field. Bacterial streaming was observed from rind sections
cut from the blotch margins. A gram-negative, nonfluorescent, oxidasepositive,
rod-shaped bacterium was isolated from diseased fruit tissues.
The bacterium grew at 41 C and did not utilize glucose or sucrose
as a sole carbon source. The characteristics of the bacterium were
consistent with those described for the fruit blotch pathogen by Somodi
et al (1). Pathogenicity of the bacterium on watermelon was verified
after spray and stab inoculations of 2-wk-old watermelon seedlings
(cv. Jubilee II) with a suspension of 1011 cfu/ml in 0.85% NaCI (saline).
Inoculated seedlings were incubated in plastic bags. Water-soaked
lesions developed on cotyledons, true leaves, and stems within 2 days.
No lesions developed on control seedlings sprayed or stabbed with
sterile saline. Koch's postulates were completed by reisolating the
bacterium from inoculated plants.