DETECTION OF 2 RACES OF PHIALOPHORA-GREGATA F SP. ADZUKICOLA, THE CAUSAL AGENT OF ADZUKI BEAN BROWN STEM ROT

Adzuki bean brown stem rot (BSR) is endemic on Hokkaido Island and has been controlled since 1985 by using resistant cultivars. BSR was repo rted on the resistant cultivar Kita-no-otome in a field near Memuro-ch o, and this study was undertaken to determine if pathogenic races were present. The existence of avirulent and virulent isolates of the path ogen to cultivar Kita-no-otome was shown by comparing the virulence am ong six isolates (T96-1, T96-2, T96-3, T96-4, T96-5, and S95-1) obtain ed from diseased plants or naturally infested field soils. Three out o f six isolates caused no disease on Kita-no-otome (DSI = 0), whereas t he other three isolates were virulent on this cultivar (DSI = 1.2 to 2 .6). In additional experiments, another three lines, Toiku No. 125, To iku No. 132, and Toiku No. 140, derived from various gene sources, als o revealed the same response to two representative isolates (T96-1 and T96-5) tested as with Kita-no-otome. Consequently, two races of Phial ophora gregata f. sp, adzukicola, race 1 and race 2, can be distinguis hed by avirulence or virulence to Kita-no-otome, respectively.