Heat-Tolerant QTLs Associated with Grain Yield and Its Components in Spring Bread Wheat under Heat-Stressed Environments of Sudan and Egypt

Heat stress decreases photosynthesis, pollen viability, grain number and weight, and hence lowers yield and quality of wheat by variable amounts among different cultivars and genotypes. The present study was carried out to determine genetic variability of spring bread wheat genotypes for yield and other agronomic traits under heat stressed (Wad Medani, Sudan) and high yielding (Sids, Egypyt) environments, and identify linked SNP markers through association mapping. A heat association panel (HAP) of 197 spring wheat genotypes from the International Center for Agricultural Research in the Dry Areas (ICARDA) was evaluated for yield and agronomic traits at Wad Medani and Sids stations for two years (2014-2015). Out of the total 15K SNPs used for genotyping, 10577 SNPs were found to be polymorphic and used for the analysis. Significant grain
yield variation (p < 0.001) was detected among genotypes with nearly two- to four-fold variation among estimated means at the Sids and Wad Medani stations, respectively. A total of 111 significant marker-trait associations (MTA) were detected. The wsnp_Ex_c12812_20324622 marker on chromosome 4A was significantly correlated with yield at both locations. At Wad Medani, wsnp_Ex_c2526_4715978 on chromosome 5A was significantly correlated with grain yield. Wheat genotypes carrying the cytosine base at the wsnp_Ex_c12812_20324622 and wsnp_Ex_c2526_4715978 markers out-yielded the ones carrying the alternative bases by 15% while genotypes carrying the cytosine base at only one of the two markers increased their yield by 7.9-10%, suggesting the importance of using these markers for MAS in breeding programs to increase yield under heat stress. The top 20 high yielding and heat tolerant genotypes identified in this study have been distributed to the national research systems in the CWANA (Central and West Asia and North Africa) and SSA(Sub Sahara Africa) regions through our international nursery system for potential direct release and/or use as parents after local adaptation trials.