GENETIC-RELATIONSHIPS AMONG AND SELECTION FOR RICE YIELD AND YIELD COMPONENTS

Genetic correlations provide useful information to plant breeders for developing selection schemes. Genetic correlations among yield and yie ld components (panicle number, panicle weight, panicle length, primary branches, and plant height) for U.S. southern long-grain rice (Oryza sativa L.) have not been reported. The objectives of this work were to estimate and use genetic correlations in developing selection methodo logies in rice breeding programs. In 1989, two 4 x 4 crossing factoria ls (Design II) were completed, and the 32 F1 hybrids and the 16 parent s were evaluated in 1990 at two Arkansas locations (Stuttgart and Mari anna). Additive genetic and broad-sense genetic correlations were esti mated. At both the additive and broad-sense genetic levels, yield was positively correlated with panicle weight. Yield was negatively correl ated with panicle number, but the effect was diminished at the broad-s ense genetic level. Panicle weight was negatively correlated with pani cle number. Path analysis, however, revealed positive direct effects f or both panicle number and panicle weight on rice yield at both the ad ditive genetic and broad-sense genetic levels, with panicle weight exh ibiting larger direct effects on yield than panicle number. Selection indices were developed from the additive genetic and phenotypic varian ces and covariances. The selection indices indicated that selecting fo r increased yield via selection for either panicle weight or panicle n umber alone would be ineffective. A selection index that included sele ction for both increased panicle weight and panicle number to increase yield was estimated to be 91% as effective as selecting for yield dir ectly.