Sorting-out of New Isolates Pathogenic against the Tongil Varieties of Korean Rice from a Japanese Rice Blast Fungus (Pyricularia oryzae Cavara)

Abstract

One isolate (Naga 64-8) among rice blast fungi (Pyricularia oryzae Cavara) isolated in Japan formed a very few susceptible lesions on Milyang 23 and Yushin of the Tongil variety group of Korean rice. All the reisolates from their lesions were severely pathogenic against the two Tongil varieties. On the other hand, reisolates from the lesions on Japanease rice varieties inoulated by the isolate of Naga 64-8 and those from the spores of the isolate on an oat-meal decoction agar medium contained both the pathogenic and the nonpathogenic isolates against the Tongil varieties. All their isolates showed the same reactions to the Japanease differentials as the isolate of Naga 64-8. The above results showed that the mother isolate of Naga 64-8 (033) contained two types of spores differing in pathogenicity against the Tongil varieties. Thus, we presumed that the isolate pathogenic against the Tongil varieties might sort out during successive culturing of the fungus by mutation.