Evaluating the relationships between grain yield and important agronomic traits in cultivars and promising lines of grain sorghum under non-stress and drought stress irrigation regimes

To evaluate the relationships between grain yield and some important agronomic traits in grain sorghum cultivars and promising lines, an experiment was conducted as a split plots arrangement based on randomized complete block design with three replications in Seed and Plant Improvement Research Institute, Karaj, Iran, during two growing seasons 2013-2014. Irrigation treatments as the main factor at three levels (normal irrigation or non-stress, mild water stress and severe water stress) and genotypes as sub-factor at five levels (Kimya, Sepideh, KGS15, KGS23, and KGS32) were considered. The results of combined analysis of variance for morphologic and yield traits showed that there was the significant differences at 1% probability level among the genotypes for all studied traits. Evaluation of the stress tolerance index (STI) and geometric mean productivity (GMP) showed that the genotypes Kimiya and KGS23 with grain yield of 9162.5 and 8521.9 kg.ha-1, respectively under non-stress and 6644.0 and 6578.0 kg.ha-1, respectively under severe stress conditions, were determined as tolerant genotypes in this research. The results of genetic correlation coefficients among traits under normal and stress conditions indicated that there was a significant positive correlation between grain yield and panicle length, stem diameter, panicle weight, fresh forage yield, biologic yield, number of grain per panicle and 1000-grain weight. The result of path analysis for grain yield showed that panicle weight and 1000-grain weight had a considerable positive direct effect on grain yield under both non-stress and drought stress conditions, but biologic yield had a little negative direct effect under non-stress and a high positive direct effect under drought stress. Therefore, indirect selection using panicle weight and 1000-grain weight is recommended for improving grain yield of sorghum.