Mode of gene action of inheritance for resistance to rice yellow mottle virus

Abstract

Rice (Oryza glaberrima) yellow mottle virus (RYMV) causes significant economic damage to rainfed and lowland irrigated rice, Oryza sativa L. in West and East Africa. This study investigated the mode of gene action of resistance to RYMV using generation mean analysis. Crosses were made between a more susceptible line (Tog 7258) and three resistant pure lines to produce the F1 , F2, backcrosses and F3 populations necessary to conduct the genetic studies. The seven populations were grown in a screen house at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria in 1992 and 1993. Severity of mottle symptom on plants was classified on a 0 - 9 scale based on the intensity of the disease on leaves under artificial virus inoculation. In general, F1 disease scores were higher than the mid-parental value. Mather’s scaling test was applied to the data generated from each cross and the results indicated that generation means depended on additive and dominance gene effects. An epistatic effect was suggested in the generation mean analysis using Hayman’s method and the primary effect was assumed to be additive and dominance and their interactions as indicated in the scaling test. Estimates of gene numbers indicated that the two parents were different by 2 to 4 genes for resistance to RYMV. Narrow sense heritability was estimated to be 44-65% and, therefore, a breeder should be able to make progress by selecting in the F2 or F3 generation.