Ecologic and taxomic studies on Pythium as pathogenic soil fungi

Strawberry root-rot is caused by several species of Pythium. Considerable number of works has been published concerning the disease but the identification of the causal fungi was entirely neglected or over-looked. This work, therefore, seeks to know the identities of the causal organisms.Taxonomic studies revealed that there are 3 species aside from an undescribed species of Pythium that are pathogenic to strawberry. The 3 known species are Pythium oedochilum Drech., P. debaryanum Hesse, and P. mamillatum Meurs. A new species, Pythium fragariae was described as follows: Hyphae are coenocytic, irregularly branched, 6-8μ in width, sparingly septate with age. Sporangia are abundant on corn-meal agar, terminal and intercalary, spherical to oval, 9.9-35.5μ in diameter, average 21.4μ; germinate directly or by formation of vesicle with a short tube; 10-15 zoospores are in a vesicle. Oogonia are abundant but fewer and smaller than sporangia, terminal and intercalary, spherical to sub-spherical, smooth, very rarely with a single spine, 8.9-23.7μ in diameter, average 19.7μ. Oospores are spherical and smooth, completely filling the oogonia though very few are not, 7.5-22.5μ in diameter, average 17.0μ, thick-walled when mature. Antheridia are stalked or intercalary, rarely diclinous, hypogynal, commonly one and very seldom 2-3 to an oogonium.Pythium oedochilum and P. debaryanum were isolated from diseased roots of strawberry collected from Ikeda City, Osaka prefecture in June, 1960, and P. fragariae was isolated in May, 1960, in Yao City of the same prefecture. Pythium mamillatum was isolated in April, 1962 at Shizuoka Agricultural Experiment Station and also identified as the cause of strawberry root decay in Kunouzan, Shizuoka prefecture.