Fusarium oxysporum f. sp. adzukicola, causal agent of adzuki bean wilt, and detection of three races of the fungus.

Abstract

We confirmed that a wilt of adzuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) in Hokkaido is caused by a new forma specialis of Fusarium oxysporum reported by Kitazawa and Yanagita as Fusarium oxysporum f. sp. adzukicola. We also suggested “Adzuki icho-byo” as the Japanese name of adzuki bean wilt caused by Fusarium oxysporum f. sp. adzukicola. The susceptibility of adzuki bean cultivars and lines to adzuki bean wilt was determined in greenhouse and field tests. For greenhouse tests, the roots of 7- to 10-day-old seedlings grown in sterilized vermiculite were dipped for about 1hr in a suspension of spores of Fusarium oxysporum f. sp. adzukicola (106 microconidia/ml) and the seedlings were then transplanted into pots filled with sterilized soil. Plants for these tests were grown at temperatures between 18∼33C. Initial symptoms on susceptible plants appeared about 10∼14 days after inoculation. The typical symptoms observed in the greenhouse test were similar to those observed on plants grown in fields. The response of 22 cultivars and lines to eight isolates of F. o. f. sp. adzukicola resulted in the identification of three races of the fungus. The reaction of cultivars in field tests were similar to those for race 3 in greenhouse tests. It was concluded that screening of adzuki bean germ plasm in greenhouse tests is effective in selecting for resistance.