Sustainable crop production in a changing climate is necessary to feed the world's expanding population. As a cool-season crop, wheat has an excessive sensitivity to temperature crossed the optimum. More challenging, above 40% of wheat growing regions are currently experiencing an increased temperature beyond the optimum. Therefore, breeding to improve wheat for heat stress tolerance is necessary. Crop breeders are usually utilizing genetic variation to enhance crops against environmental stresses. However, most wheat cultivars have relatively narrow genetic diversity associated with selection on yield per se, seriously restricting its selection for heat stress tolerance breeding. Hence, a practical solution is to expand their genetic base using the adaptive capacity resources of wild progenitors. One of such resources is the wild emmer wheat (Triticum turgidum ssp. dicoccoides), a direct progenitor of domesticated durum wheat (T. durum), and the A and B genomes of bread wheat (T. aestivum). Interestingly, the natural variation of wild emmer wheat possesses important agronomic, physiological, and yield-related traits associated with heat stress tolerance. Thus, this diversity in wild emmer wheat is needed to sustain and improve wheat tolerance against heat stress.

Here, a diverse set of Multiple Derivative Lines (MDLs) was developed by crossing and backcrossing nine wild emmer wheat (Triticum turgidum L. ssp. dicoccoides) with durum wheat cultivar (T. durum). These materials and their recurrent parent were evaluated under four environments; two optimum environments in Japan, Tottori, and Sudan, Dongola, one heat stress, and one severe heat stress at Wad Medani, Sudan. This study aims to identify germplasm and QTL associated with heat stress tolerance and to evaluate the valuable diversity of the wild emmer wheat for heat stress resilience.

Using genome-wide association analysis, we identified strong marker-trait associations (MTAs) for chlorophyll content at maturity on chromosomes 1A and 5B, which explained 28.8 and 26.8% of the variation, respectively. A region on chromosome 3A (473.7-638.4 Mbp) contains MTAs controlling grain yield under optimum and severe heat stress. Under severe heat stress, we identified regions on chromosomes 3A (590.4-713.3 Mbp) controlling grain yield, biomass, days to maturity and thousand kernel weight, and on 3B (744.0-795.2 Mbp) common to the grain yield and biomass. Heat tolerant efficiency (HTE) was controlled by three MTAs, one each on chromosomes 2A, 2B, and 5A under heat stress, whereas under severe heat stress, one MTA is associated with HTE on chromosome 3A. Some of the MTAs found here were previously reported, and the new ones were originated from the wild emmer wheat genomes. We identified three alleles from the wild emmer wheat genome that increased biomass, chlorophyll content at maturity, and thousand kernel weight under severe heat stress. Interestingly, these alleles were not presented in the elite durum wheat lines being bred for heat stress tolerance. This study provides potential genetic materials, alleles, MTAs, and QTLs for enhancing wheat adaptation to heat stress. Furthermore, the MDL lines with favorable wild emmer wheat alleles identified in this study can be used as an excellent source to improve the A and B genomes of durum and bread wheat to adapt to heat stress.