Detection of Two 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 reported on the resistant cultivar Kita-no-otome in a field near Memuro-cho, and this study was undertaken to determine if pathogenic races were present. The existence of avirulent and virulent isolates of the pathogen to cultivar Kita-no-otome was shown by comparing the virulence among six isolates (T96-1, T96-2, T96-3, T96-4, T96-5, and S95-1) obtained from diseased plants or naturally infested field soils. Three out of six isolates caused no disease on Kita-no-otome (DSI = 0), whereas the other three isolates were virulent on this cultivar (DSI = 1.2 to 2.6). In additional experiments, another three lines, Toiku No. 125, Toiku No. 132, and Toiku No. 140, derived from various gene sources, also revealed the same response to two representative isolates (T96-1 and T96-5) tested as with Kita-no-otome. Consequently, two races of Phialophora gregata f. sp. adzukicola, race 1 and race 2, can be distinguished by avirulence or virulence to Kita-no-otome, respectively.