INHERITANCE OF RESISTANCE IN RICE TO RACES IB-49 AND IC-17 OF PYRICULARIA-GRISEA RICE BLAST

Rice blast [Pyricularia grisea (Cooke) Sacc.] is an internationally devastating rice (Oryza sativa L.) disease. This study was conducted to determine the inheritance of rice blast resistance to the blast fungus races IB-49 and IC-17. Nine parents were crossed in all possible combinations. Parents, F1, F2, and selected F2-derived lines in the F3 were tested for their reactions to blast fungus races IB49 and IC-17 separately in the greenhouse during 1986 and 1987. The parents 'Starbonnet', 'Newbonnet', and 'M-201' were susceptible to both races; 'Raminad Strain 3', 'Pi No. 4', and 'Katy' were resistant to both races; 'Mars' and 'Zenith' were susceptible to race IB-49 and resistant to race IC-17; and 'NP 125' was susceptible to race IC-17 and resistant to race IB-49. Inheritance of resistance to race IC-17 was dominant and monogenic in crosses involving resistant parents. Inheritance to race IB-49 was dominant and monogenic in crosses with the parents Raminad Strain 3, Pi No. 4, and Katy, but was controlled by two dominant complementary genes in crosses involving NP 125. Allelic relationships among the resistant parents indicate that one locus controlled the resistance to race IB-49 and three loci controlled the resistance to race IC-17. Resistance to both races was conferred by one gene or group of tightly linked genes in Katy. Diverse sources of resistance are necessary to avoid genetic vulnerability. Resistance to race IC-17 and IB-49 is simply inherited and should be relatively easy to incorporate into rice cultivars.