DIFFERENTIATION OF VIRULENCE IN RHYNCHOSPORIUM-SECALIS IN THE HOKURIKU DISTRICT AND SOURCES OF RESISTANCE TO THE PATHOGEN

Variation of virulence in Rhynchosporium secalis (Oud.) Davis distribu ted in the Hokuriku district was investigated by seedling infection te st using 14 differential barley cultivars. A total of 38 cultures were isolated from the infected leaves of Minorimugi, a leading variety in the Hokuriku area, in 1992, 1993 and 1995 from various locations. The 38 isolates showed a complex variation in the virulence pattern and c ould be classified into 36 different pathotypes according to the virul ence spectra to the differentials. Based on the cluster analysis of th e reactions of 14 differentials, a geographical dine for virulence was suggested; the isolates from the southern part of the district (Fukui , Ishikawa and Toyama) were more virulent to the differentials than th ose from the northern part (Yamagata and Niigata). This fact suggests that the virulence of the fungus is conditioned by not only race-speci fic gene (s) but also by some genes with interactions such as additive or complementary effects. Among the 14 differentials, Brier, Turk and Osiris were highly resistant to the 38 isolates. It appeared that the resistance of these 3 cultivars was controlled by different gene (s) from Rh, Rh-4, Rh5, rh6 or Rh10, since other differentials with the sa me genotype were attacked by many of the isolates. The 17 cultivars, w hich had been already selected for the resistance to the Niigata isola te, were tested by 32 of the 38 isolates above mentioned, and 3 cultiv ars, Turkey 22, Trukey 208 and Carre 26, were confirmed to be highly r esistant to all the isolates. It was concluded that these cultivars in cluding Brier, Turk and Osiris are highly suitable materials for breed ing for resistance to scald in the Hokuriku district.