Assessment of Genetic Diversity in Bread Wheat Genotypes Based on Heat Tolerance and SSR Markers

Ten bread wheat genotypes (Triticum aestivum L.) were evaluated for heat tolerance under normal and late sowing dates during 2014/2015 and 2015/2016 seasons. Four agronomic traits, i.e. grain yield per plant (GYP), 1000-kernel weight (TKW), Spike length (SL) and plant height (PH) were evaluated. The genetic diversity was assessed among genotypes based on phenotypic data and thirteen simple sequence repeats (SSR) markers, representatives of nine wheat chromosomes. Heat stress under the late sowing date was quite strong resulting in 30.4, 14.6, 14.7 and 28.8% average reduction for GYP, TKW, SL and PH, respectively. GYP showed a negative and significant correlation (r= -0.66, P<0.05) with heat susceptibility index (HSI) under heat stress. By using 13 SSR markers, a total of 125 DNA fragments were generated, with an average of 9.6 bands per marker. The level of polymorphism (%P) ranged from 25% for the marker Xgwm497-1A to 85.7% for Xwmc273-7A, with an average of 60.8%. The highest polymorphism information content (PIC) value (0.36) was also recorded for Xwmc273-7A, while the lowest PIC (0.11) was found with Xwmc398-6A, with an average of 0.23. A highly significant correlation (r= 0.872, P<0.01) was found between %P and PIC values. Cluster analysis based on phenotypic data classified the ten genotypes into two groups, of which the group-1 genotypes (Line-1, Line-2 and Line-3) showed high tolerance to heat stress by exhibiting lowest HSI values. However, cluster analysis based on SSR markers generated two clusters, where cluster-I contained five genotypes (Line-1, Line-2, Line-3, Debeira and EL-Nilein) tolerant to heat stress, indicating the efficiency of SSR markers in discriminating wheat genotypes. Moreover, four SSRs generated some unique bands or specific for some tolerant genotypes, that could be used as markers associated with heat tolerance in wheat. However, additional markers analysis is still required to validate their usefulness in breading programs.