Genetic diversity in wheat genotypes under early heat stress in Bangladesh

Twenty-four wheat genotypes were evaluated in alpha lattice design with three replications at the Regional Wheat Research Centre (RWRC), Bangladesh Agricultural Research Institute (BARI), Rajshahi during Rabi season of 2014-15. The main objective of this study was to identify the extent of genetic diversity for traits related to early heat tolerance mechanism. Genotypes were grouped into five different clusters. Cluster Ⅰ and Ⅴ had same number of genotypes i.e. three and they were the smallest cluster. Maximum eight entries were grouped into the cluster Ⅲ followed by six in cluster Ⅳ, and four in cluster Ⅱ. The inter-cluster distances ranged from 3.4496 to 6.8221 and principal component analysis scores also indicated a high degree of genetic diversity among the genotypes. The maximum inter-cluster distance was observed between the clusters Ⅳ and Ⅴ (6.8221) followed by the distance between cluster Ⅰ and Ⅳ (5.8935) and between clusters Ⅲ and Ⅴ (5.2913). The maximum value of inter-cluster distance indicated that the genotypes belonging to cluster Ⅳ were far diverged from those of cluster Ⅴ. Similarly, the higher inter-cluster values between cluster Ⅰ and Ⅳ, clusters Ⅲ and Ⅳ indicated that the genotypes belonging to each pair of clusters were far diverged. The minimum inter-cluster diversity was observed between cluster Ⅲ and Ⅳ (3.4018), cluster Ⅰ and Ⅴ (3.4496), cluster Ⅰ and Ⅱ (3.6163) and cluster Ⅱ and Ⅳ (4.1373) indicating that the genotypes of these clusters were genetically closed. However, the highest spike length, spikelets spike-1 and grain yield were found in cluster Ⅰ may exhibit high heterosis for yield. Again, considering short growing duration, dwarf stature and bold grain were aggregated in cluster Ⅳ may exhibit higher heterosis for earliness and dwarf stature. Canonical variety analysis (CVA) revealed that spike length and 1000-grain weight had positive values in both vectors which indicated that these two traits had the highest contribution towards the divergence. Based on these results, the genotypes under cluster Ⅰ, cluster Ⅴ and cluster Ⅳ might be selected for future early heat tolerance wheat breeding program.