Genetic parameters of variability, correlation and pathcoefficient studies for grain yield and other yield Attributes among rice blast disease resistant genotypes of rice (Oryza sativa L.)
Twenty one rice genotypes were selected and screened under artificially controlled conditions to identify the rice blast disease reaction. Sixteen genotypes which were already reported to have resistance genes reacted negatively to the blast disease. Four genotypes were found to be susceptible. Highly significant, lower mean disease reaction score and mean PDI (potential disease incidence) % was recorded for Moroberekan, followed by Columbia 2 and ARBN 142 (Asian rice biological network). All the 21 genotypes along with 64 hybrids were evaluated for nine traits in a randomized block design over five replications. Genetic variability, character association and path-coefficient analysis were studied. Grain yield was kept as a dependant character and the results were analyzed. Analysis of variance revealed considerable variability among the genotypes for all the characters. The phenotypic correlation coefficient (PCV) values were slightly greater than genotypic correlation coefficient (GCV), revealing negligible influence of environment in character expression. High heritability coupled with high genetic advance and high GCV were observed for number of tillers/plant followed by number of productive tillers per plant, plant height and grain yield / plant. Characters like plant height, number of tillers / plant, number of productive tillers / plant, panicle length, filled grains per panicle and test weight had significant positive association with grain yield. Results of path-coefficient analysis revealed that, test weight exhibited maximum positive direct effect on grain yield / plant followed by filled grains / panicle, plant height, panicle length, number of tillers / plant and days to 50% flowering and they contributed primarily to yield and could be relied upon for selection of genotypes to improve genetic yield potential of rice.
Key words: Oryza sativa, direct effect, heritability, genetic advance, association, Magnaporthe grisea, phenotypic correlation coefficient, genotypic correlation coefficient.