ESTIMATION OF FUNCTIONAL VALUES OF FIELD-RESISTANCE GENES TO BLAST DISEASE IN SOME RICE VARIETIES

F3 lines of the hybrids of some varieties and Japanese susceptible var ieties were tested with two Japanese blast fungus strains, Ken 54-20 ( race number, 003.0) and Ao 14-20 (337.3), to learn the mode of inherit ance of blast resistance. Varieties used were as follows : Chinese var ieties (Sifeng 43, Quan-wei-ai and Nan Jing 11), Korean varieties (Mil yang 23, Raekyeong, Ir 338), IRRI's varieties (IR 24, IR 36 and IR 206 1), Indian varieties (RP 9-3 and CR 44), and Hokuriku 129 (Habataki). Analyses after tests were carried out by cumulative frequency distribu tion curve method by Kiyosawa. In this study, plants were divided into three groups, r, m and s, based on the degree of resistance, and resi stance genes were divided into two. One was the major gene which had a functional value of 1 and the other was the minor gene which had a fu nctional value lower than 1 in a segregation of r : (m + s). The funct ional value of 1 means that plants which had its genotype show resista nt reaction in 100 % of plants. The resistance of these varieties was explained by assuming some major genes and minor genes. Sifeng 43 has one major gene and one minor gene. Quan-wei-ai and Nan Jing 11 have tw o minor genes with their additive (or complementary) effect. It was su ggested that there are minor genes controlling resistance in intermedi ate type (m) in Milyang 23, Raekyeong, Iri 338, IR 24 and IR 36. IR 20 61 has two or more major genes and some minor genes. Resistance of Hok uriku 129 was explained by two major genes. At the least, Milyang 23, Raekyeong, Iri 338, IR 24, IR 36 and CR 44 were suggested to have Pi-b .