Abstract
A fungus was isolated from rotten, dark-brown to black roots of wax gourd stock (Benincasa cerifera Savi) of watermelon plants in Nagano and Kanagawa Prefectures. The fungus was identified as the charcoal rot fungus Macrophomina phaseolina (Tassi) Goid., an omnivorous soilborne pathogen, on the basis of its morphological characteristics, thermophilic nature and inoculation experiments. This is the first report of watermelon charcoal rot caused by M. phaseolina in Japan. The pathogenicity of the fungus on several plants was clarified. Crop rotation to avoid increasing inoculum density of the pathogen is discussed.
