Japanese Journal of Phytopathology

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A new medium for the isolation of Pseudomonas syringae pv. theae was developed. This medium (PST-SM) contains 20g of proteose peptone, 10ml of glycerol, 1.5g of disodium hydrogen phosphate, 1.5g of magnesium sulfate, 250mg of cephalexin, 100mg of cycloheximide and 12g of agar in 1000ml of distilled water, and adjusted to pH 7.2. P. syringae pv. theae produced an opalescent colony, which was distinguishable from most bacteria tested (34 species in 4 genera) when incubated at 25°C from 2 to 4 days. The most characteristic sign of the colony of the wild type strain of P. syringae pv. theae was recognized as a fried-egg type colony with granular and fibril structures when it was irradiated with light in an oblique downward direction from a light microscope at 2 days after incubation. Plating efficiency of this medium to P. syringae pv. theae was the same as King's B medium. P. syringae pv. theae could be detected selectively from infected tea plant tissue with a selective limitation of more than 10² cfu per gram of tissue.

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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.

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In 17 areas of paddy field alongside the Morimoto River in Kanazawa, rice plants and the weed Leersia infected with Xanthomonas oryzae pv. oryzae were screened and assayed by PCR. Diseased rice plants were found in eight of 17 areas. Of these eight areas, diseased and PCR-positive Leersia plants were found in four areas; asymptomatic but PCR-positive Leersia were found in two areas; no Leersia was found in two areas. In the remaining nine areas, all Leersia were asymptomatic and PCR-negative. In conclusion, PCR assay could be useful for detecting the pathogen and can be used as a forecasting method for bacterial blight of rice.

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