HERITABILITY AND GENOTYPE X ENVIRONMENT INTERACTIONS FOR STRAIGHTHEAD IN RICE

Straighthead is a physiological disorder of rice (Oryza sativa L.), which is manifested by floret sterility resulting in yield loss. The objectives of this study were to estimate the narrow-sense heritability (h(2)) and the relative importance of genotype x environment interactions for straighthead and to suggest an optimum experimental design for straighthead screening. Ten commercial cultivars and 22 randomly chosen experimental lines representing southern USA rice germplasm were tested from 1991 to 1993 at three Arkansas locations: Stuttgart [Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf)], Marianna (Loring silt loam [fine-silty, mixed, thermic Typic Fragiudalf)], and Colt [Calloway silt loam (fine-silty, mixed, thermic Glossaquic Fragiudalf)]. Straighthead was induced by monosodium methane arsenate [4.48 kg a.i. ha(-1)] incorporated into the soil before planting combined with a permanent flood established at the five-leaf stage and maintained at each location. The genotype x year and the genotype x location interaction variance components were near zero. The three-way interaction was significant, but its variance component was one-fourth the magnitude of the genetic variance. The nature of the genotype x environment interaction was explored by determining the number of significant crossover (rank change) interactions. There were 798 significant crossover interactions or 4.5% of the possible 17 856 quadruples. Thus, genotype x environment interactions were minor and due primarily to changes in magnitude rather than to changes in rank. Heritability (single plot basis) was 61%, indicating that selection for resistance to straighthead should be relatively easy in southern U.S. rice germplasm. Two locations with four replications per location should be adequate for screening southern U.S. rice germplasm for reaction to straighthead.