Genomic dissection of terminal heat tolerance in synthetic hexaploid derived nested introgression libraries of wheat (Triticum aestivum L.).

The terminal heat stress during grain filling period is major threat to wheat productivity. Heat tolerant QTLs were harnessed from synthetic hexaploid lines (SHWs) derived from heat tolerant Ae. tauschii accessions in present study. SHWs were crossed with two heat susceptible advanced breeding lines to develop nested introgression libraries (S-NILibs). The S-NILibs were evaluated for phenotypic traits and heat tolerance index (HTI) over three years under optimum environment (OE) with sowing at normal date in mid-November and heat stressed environment (HSE) under sown late during mid-December. The panel of 354 S-NILibs was genotyped using the 35 K Axiom® Wheat Breeder's Array. Genome-wide association study (GWAS) identified a total of 61 marker-trait associations (MTAs) across environments (OE and HSE), associated with different traits using multiple models. Of these, two MTAs AX_94985380 for plant height (PH), spikelet number (SN) and AX_94469933 for plant height (PH), thousand grain weight (TGW) were observed for more than one trait across environments and models. Another MTA for HTI (AX-94461626) mapped on 4B chromosome was observed in all four environments and three models. This MTA originated from genes for Ubiquitin carboxyl-terminal hydrolases which is known for maintenance of the circadian clock at high temperature. A subset of MTAs was validated using KASP markers suggested strong association with traits of PH, SN, flag leaf length (FL) and number of productive tillers (pTN). The S-NILib generated, and QTLs identified in this study are potential pre-breeding resource for heat stress tolerance.