Aphanomyces species parasitic on cruciferous crops were isolated from 20 vegetable field soils of 6 prefectures, Nagano, Saitama, Tottori, Gunma, Kanagawa, and Iwate in Japan proper. Cultural properties, host ranges and morphology were investigated with 4 isolates (N, S, T, and G from Nagano, Saitama, Tottori and Gunma, respectively) of these Aphanomyces isolates.
Of 7 families of crops tested, only cruciferous crops were attacked by the 4 isolates.
Growth of isolates was good on potato-dextrose agar and radish agar, and except isolate T, methionine agar also gave considerable growth. These isolates grow between 5-35°C, with the optimum temperatures at 23-28°C.
Inhibitory effect of streptomycin sulphate on growth was hardly observed at 50 and 100ppm in potato-dextrose agar. Streptomycin can be used in isolation media.
From measurements of oogonia and oospores of these isolates, isolate N and S correspond to Aphanomyces raphani of Drechsler and isolate T and G correspond to A. raphani of Tsuchiya, et al. Behaviour of antheridia on oogonia agrees with the Drechsler's descriptions. Judging from the morphological characteristics and pathogenesis, these 4 isolates were identified as A. raphani Kendrick.