Detection of Two Races of Phialophora gregata f. sp. adzukicola, the Causal Agent of Adzuki Bean Brown Stem Rot

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Abstract
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.