The Use of Genotypic Path Coefficients to Make Optimum and Base Selection Indices in Rice

Grain yield and most of the traits that have economic importance in plants and animals, are inherited quantitatively and using direct selection methods don,t result in larger gains. One of the effective indirect selections methods for improving grain yield and its components is the selection index. In this study, 109 F2 plants that was produced from a cross between Hashemy and Kadous rice varieties were evaluated to determine suitable selection indices. Studied traits were number of days to maturity, plant height, panicle length, flag leaf length, flag leaf width, panicle per plant, grains per panicle, spikelets per panicle, 100-grain weight, grain yield per plant, biomass, harvest index, grain length and grain width. Results revealed that biomass and flag leaf width had highest and lowest, broad sense heritability, respectively. Grain yield had significant positive genetic correlations with grains per panicle, biomass, harvest index, spikelets per panicle, panicle per plant, flag leaf length, panicle length and grain width. Result of path analysis revealed that biomass, harvest index, spikelets per panicle and flag leaf width had positive direct effects on the grain yield while number of days to maturity showed negative direct effect on grain yield. Ten different selection indices based on optimum and base indices were investigated for improving grain yield and yield components. The direct genetic effects (genetic path coefficients) of biomass and harvest index were high. Therefore, an index based on these characters using their genetic path coefficients as economic values, will be useful to select for grain yield. Also for the traits that have higher heritability than grain yield, the use their genetic correlation coefficients with the grain yield as economic values would be a better index for the population improvement. Furthermore, the genetic gain from optimum and base indices were almost similar. However, the base index is recommended due to the easiness of computations and interpretation of results.