Recognition the effective traits on grain yield of bread wheat genotypes under heat stress and non-stress conditions

To determine the traits affecting grain yield, 10 bread wheat genotypes including Morvarid and Kohdasht cultivars and Lines of N-87-4, N-87-9, N-86-6, N-86-8, N-80-19, N-86-5, N-85-5 and Line 17 were planted in two separate experiments including environmental conditions without heat stress in 15 December, and heat stress conditions of 10 February in Gonbad Kavous Agricultural Research Station during 2011-2012. Genotypes were compared in a randomized complete block design with three replications andwith combined analysis. Interaction of heat stress and genotypes were significant for grain yield, spike length, number of fertile spike. Genotypes and heat stress effect in all recorded traits were significant. In both conditions, grain yield had a positive and significant correlation with number of fertile spikes. Stepwise regression showed that the number of fertile spikes in normal conditions 99.8% and in heat stress 97.1% of grain yield changes were explained. The path analysis showed that the number of fertile spike had the most direct effect on grain yield in both conditions. The cluster analysis categorized genotypes into two group in normal conditions and three groups in heat stress conditions. Therefore, the number of fertile spikes can be used indirectly in the selection of genotypes with high yield in both heat and normal conditions.