ASSESSING THE EARLY-SEASON VIGOR OF A DIVERSE RICE POPULATION BY USING MORPHOPHYSIOLOGICAL TRAITS

Early-season vigor is an important morphological determinant of a crop's growth rate and duration. It results from metric parameters, such as light interception and dry matter production, loss, and partitioning. Formulating screening tools to assess early-season vigor by using root and shoot characteristics will be useful for identifying genotypes with superior performance during the juvenile growth stages. A 2-year study was conducted by using a sunlit pot culture set-up to assess genetic variation among 100 rice genotypes for shoot and root traits and several physiological parameters at the seedling growth stage (25-30 days after sowing). Given the absence of a significant year or experimental period x genotype interaction for the traits measured, the 2-year data were combined for each genotype. Individual (IVRI) and cumulative response indexes (CVRI) were estimated for each trait for all genotypes. Genotypes were classified into different categories by using CVRI values and standard errors. The majority of the genotypes exhibited low vigor (43%), followed by genotypes with moderate (33%) and very low (16%) vigor. However, five and three genotypes showed high- and very-high vigor, respectively. The CVRI values varied from a low value of 21.36 for RU1404196 to 36.17 for N-22, the most vigorous genotype. The high-vigor genotypes can be valuable genetic resources for developing new varieties with high early-season vigor as well as for physiological studies on canopy development for optimum light interception and weed competitiveness. The information and methods generated by this study can also be useful in identifying promising rice lines with potentially high vigor in rice breeding programs.