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Pythium Species Associated with Strawberry Roots in Japan, and Their Role in the Strawberry Stunt Disease. Tsuneo Watanabe, Department of Plant Pathology and Entomology, National Institute of Agricultural Sciences, Nishigahara, Kita-ku, Tokyo, Japan; Koji Hashimoto(2), and Masanao Sato(3). (2)Plant Pathology Laboratory, Saitama Horticulture Experiment Station, Kuki, Saitama, Japan; (3)Department of Plant Protection, Shizuoka Agriculture Experiment Station, Kitaando, Shizuoka, Japan. Phytopathology 67:1324-1332. Accepted for publication 15 April 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1324.

Of 58 fungus genera identified among 2,011 fungus isolates from roots of “stunted” and healthy strawberry plants collected in May 1973 to December 1974 in Japan, 60% were species of Fusarium, Pythium, and Rhizoctonia. Fourteen species were identified among the 291 isolates of Pythium spp. the most dominant of which were P. sylvaticum complex (138 isolates), P. ultimum (46 isolates), P. spinosum (42 isolates), and P. oedochilum (40 isolates). For eight of the species (P. afertile, P. angustatum, P. apleroticum, P. echinulatum, P. inflatum, P. myriotylum, P. paroecandrum, and P. torulosum this appears to be the first record of isolations from strawberry plants throughout the world. Isolations from the rhizosphere of the strawberry yielded ten species of Pythium, the most dominant of which were P. carolinianum (49 isolates), P. aphanidermatum (14 isolates), P. spinosum (11 isolates), and P. sylvaticum complex (nine isolates). Pythium aphanidermatum, P. carolinianum, and P. intermedium were isolated only from the rhizosphere soil in this study. Pythium ultimum was found to be a primary pathogen of the stunt disease of strawberry among several Pythium spp. tested at temperatures below 20 C. Pythium echinulatum, and other Pythium species also were pathogenic on strawberry roots at 26 C. Implication of P. ultimum and Pythium spp. in the occurrence of the stunt disease of strawberry in Japan is discussed in this study.