Abstract
To investigate the occurrence of strains of the tea gray blight fungus Pestalotia longiseta and P. theae resistant to benzimidazole fungisides (Topsin M, Benlate), tea leaves affected by the disease were collected from 14 major tea-producing prefectures in Japan. An isolate from each diseased leaf was examined on PDA media containing thiophanate-methyl (Topsin M) of the concentrations of 0, 1, 100 ppm. The medium inhibitory concentration (MIC) for several isolates and the geographical distribution of the tea gray blight fungi Pestalotia spp., i. e. P. longiseta, P. theae were also analyzed. In 68 tea fields out of the 119 tested resistant strains (1ppm inhibition) were detected, although highly-resistant ones (100ppm inhibition) were obtained from 54 fields. The ratio of detection of the resistant strains in Shizuoka, Mie, Saga, Miyazaki and Kagoshima Prefectures was high, whereas in Tokushima and Kochi Prefectures resistant strains were not detected. Regarding the geographical distribution of the Pestalotia spp., most of the P. longiseta species were isolated in Shizuoka, Aichi, Mie, Shiga, and Nara Prefectures. While in Saitama, Tokushima, and Kumamoto Prefectures, the P. theae species were isolated more frequently than the P. longiseta ones.
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