GENIC ANALYSIS OF RESISTANCE TO BLAST DISEASE IN RICE

BY BIOMETRICAL GENETIC METHOD

Abstract

In view of the fact that hybrids between varieties of rice with different degrees of resistance to the blast disease often show a continuous array of intergrades in the degree of infection, biometrical methods were used for genic analysis of the resistance in this study. The F₂, F₃ families and F₃ bulk population of a cross between phylogenetically distant varieties, Pei-ku×Taichung No. 65, were planted in an experimental field at Tonhsu, Taichung Prefecture, Formosa, where blast disease prevails seriously. The degree of infection was measured on a single plant basis by a series of index-numbers. Variance components (D. H and E items) were partitioned by Mather's method, and the number of effective factors was estimated. Both K₁ and K₂ were found to approach one, indicating that the main gene segregating in this cross was one pair. Judging from the mode of frequency distribution, the gene for susceptibility appeared to be dominant over its allelomorph for resistance. It was found that the resistance gene was linked with “Gametic-Development genes” (Oka 1953 a, b, c), bringing about a change in segregation ratio. It was found further that the resistance gene was linked with the phenol-reaction gene, and the recombination value was near to 0.40.