F1 heterosis over midparent (MP) and better parent (BP) and F2 inbreeding depression (10) were studied in 8 crosses of rice for grain yield/plant and its four component traits, i.e., plant height, effective tillers/plant, filled grains/panicle and 1000-grain weight. Highly significant and positive heterosis for grain yield over MP and BP was expressed by four hybrids and, invariably followed by 10 in F2. Such high grain yield heterosis was due to additive heterotic effect of one or more component traits. In all the cases, heterosis for number of effective tillers was observed to be the major contributor and number of filled grains/panicle to a lesser extent, to grain yield heterosis. High heterosis accompanied by high 10 for effective tillets/plant and filled grains/panicle indicate that nonadditive gene effects govern the inheritance of these traits. Since the hybrid vigour was not of retentive nature, as indicated by high 10 in F2 for grain yield, it can be exploited only in F1.
Heterosis, inbreeding depression, Orym sativa L
