Heterosis and inbreeding depression in upland rice crosses

F1 heterosis over midparent (MP) and better parent (BP) and F2 inbreeding depression (ID) were studied in 8 crosses of rice for grain yield/plant and its four other component traits, i.e., plant height, effective tillers/plant, No. of filled grains/panicle and 1000-grain weight. Highly significant and positive MP and BP heterosis for grain yield was expressed byfour hybrids and ID in each case invariably accompanied in F2. Such high heterosis for yield was due to additive heterotic effect of one or more component traits. In all the cases, heterosis for effective tillering was found to be the major contributor and number of filled grains/panicle contributed less to grain yield heterosis. High heterosis accompanied by high ID for effective tillers/plant and number of filled grains/panicle indicated the presence of non additive gene effects governing the inheritance of these traits. Since growth vigour was not of retentive nature as indicated by high ID in F2 for grain yield, it should be exploited in F1 itself.