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Disease Note.

Outbreak of Watermelon Fruit Blotch in the Mariana Islands. G. C. Wall, College of Agriculture and Life Sciences, University of Guam, Mangilao 96923. V. M. Santos, F. J. Cruz, D. A. Nelson, and I. Cabrera. College of Agriculture and Life Sciences, University of Guam, Mangilao 96923, and Northern Marianas College, P.O. Box 1250, Saipan 96950. Plant Dis. 74:80. Accepted for publication 20 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0080D.

In 1987, entire fields of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) on Guam and Tinian were lost to a new disease characterized by water-soaked blotches in the rind of the fruit. A nonfluorescent pseudomonad was isolated from lesions and found to be the causal agent by Koch's postulates. In determinative tests, the organism appeared similar to Pseudomonas pseudoalcaligenes subsp. citrulli Schaad et al (1), causal agent of watermelon fruit blotch. Symptoms on the rind began as small (less than 1 cm in diameter) water-soaked lesions that expanded quickly, sometimes over the entire fruit. Secondary infections soon followed, and diseased fruit rotted. We found that the pathogen can be seed borne, confirming previous reports. Diseased fruit were intercepted by quarantine personnel inspecting watermelon shipments from Tinian. Outbreaks occurring since 1987 have been mostly linked with rainy and windy weather periods.

Reference: (1) N. W. Schaad et al. Int..I. Syst. Bacteriol. 28:117, 1978.