Nature of gene action and combining ability for yield and its related traits in hybrid rice
ABSTRACT A study was undertaken with a fixed effect model i.e. line x tester mating design involving 3 CMS line and 20 elite genotypes of rice to identify heterotic combinations expressing high hybrid vigour. On the basis of overall performance the male lines, IR 35454-18-1-1-2R followed by IET 201108 and IR 52256-9-2-2-1R were identified as most promising parents having good general combining ability for grain yield and major components. Out of 60 crosses, about 30% crosses showed significant and desirable sca effects for grain yield along with its three important traits, viz., number of fertile spikelets, number of spikelets per panicle and biological yield. The crosses NMS 4A x IR 633-76-1R, IR 58025A x IR 19058-107-1R, IR 58025A x IR32419-28-3-1-3-3R, NMS 4A x IR35454-18-1-1-2R and NMS 4A x IR 5226-9-2-2-1R exhibited high estimates for parents and good sca effects, hence, they may be considered for hybrid breeding programme. The higher magnitude of sca than gca variance, greater values of average degree of dominance and lower predictability ratio was observed in all the characters studied. This suggested significant role of non-additive gene action which resulted from dominance, over dominance, epistatic and various other interaction effects. Results on gene action and combining ability indicated that both general and specific combining ability effects are important but predominance of non-additive genetic variance indicated the presence of heterozygosity in the population.