Bacterial Fruit Blotch of Watermelon in Indiana. R. X. Latin, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. K. K. Rane, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Plant Dis. 74:331. Accepted for publication 19 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0331B.
A bacterial disease significantly reduced production of watermelon
(Citrullus lanatus (Thunb.) Malsum. & Nakai) in Indiana in the
summer of 1989. More than 500 ha of watermelons in southwestern
Indiana were affected, with nearly 100 ha sustaining losses approaching
90%. Small water-soaked lesions appeared on cotyledons and true
leaves of watermelon seedlings and continued to develop on leaves
of mature plants, although no severe blighting was observed.
Approximately 2 wk before harvest. small dark green blotches
appeared on the portion of the fruit not in contact with the soil.
These blotches expanded rapidly to cover almost the entire upper
surface within 5-7 days. The lesions initially extended less than 5 mm into the fruit. As fruit matured, the rind became brown and
cracked. followed by decay. A nonfluorescent, gram-negative, oxidase-positive
bacterium was isolated from the margins of fruit and leaf
lesions. With the exception of the hypersensitive reaction (HR) test,
the characteristics of the bacterium were consistent with those described
for Pseudomonas pseudoalcaligenes Stanier subsp. citrulli Schaad et
al (1). Our strain induced hypersensitivity in tobacco, whereas the
type strain of P. p. subsp. citrulli was reported to be HR-negative
(1). Koch's postulates were completed on both watermelon fruit and
leaves by stab-inoculation using a 108 cfu/ml suspension. This is the
first report of bacterial fruit blotch in the midwestern states.