COMBINING ABILITY AND HETEROSIS IN UNITED-STATES SOUTHERN LONG-GRAIN RICE

Combining ability and heterosis estimates are excellent statistics to help discern breeding program goals and direction. Currently, combining ability and heterosis estimates for U.S. southern long-grain rice (Oryza sativa L.) are lacking, and, thus, our objectives were to estimate these parameters for rice yield, plant height, panicle number, panicle length, panicle weight, and primary branch number. In 1989, two 4 x 4 crossing factorials were completed, and the 32 F1 hybrids and their 16 parents were evaluated in 1990 at two Arkansas locations: the Rice Research and Extension Center near Stuttgart and the Cotton Branch Experiment Station near Marianna. The 16 parents constituted a representative sample of elite U.S. southern long-grain rice germplasm available to rice breeders. Hill plots consisting of single plants were planted 61 cm apart in a square grid pattern. General combining ability (GCA) was more important than specific combining ability (SCA), accounting for 70% of the variation for yield, 89% for plant height, 84% for panicle number, 60% for panicle length, 69% for panicle weight, and 85% for primary branches. Specific combining ability was significant for all traits except panicle number, indicating that nonadditive gene action was important as well. When crossing combinations are being decided, the sole use of midparent means would not adequately predict progeny mean performance. High parent heterosis for yield ranged from -16 to 68%. Heterosis for yield was due primarily to heterosis for panicle weight rather than panicle number. U.S. southern long-grain rice yields could be improved through the use of hybrid rice varieties.