Combining ability and gene action of three components of horizontal resistance against rice blast

Abstract

Understanding the inheritance pattern of traits underlying horizontal resistance (HR) against rice blast is essential for developing breeding strategies aimed at genetically controlling the disease. Eight rice (Oryza sativa L.) genotypes, along with their F2 segregants derived from a complete diallel mating design, were exposed to the rice blast pathogen to determine combining ability and gene actions for the number and size of sporulating lesions developed on the plants, and area under the disease progress curve (AUDPC), following the fixed effects model of Griffing’s Method 1. Results showed that both additive and non-additive gene actions were involved in the inheritance of lesion number (LN), lesion size (LS), and AUDPC. However, additive effects were more important, as indicated by the high ratio of general combining ability to specific combining ability found for the traits. Graphical analysis of the covariance and variances of the traits ruled out epitasis as a contributor to the limited non-additive gene action revealed for LN, LS and AUDPC. The graphical analysis further showed that dominance gene action detected in the parents was rather partial. The overall results suggest that selection for LN, LS and AUDPC could be useful for breeding rice with higher levels of HR against rice blast, using all of the parents but P1, which appeared to be the worst combiner. High estimates of heritability and phenotypic correlation were found for all three traits, which suggested that selection for the traits under controlled environment conditions would be effective in a recurrent selection programme.