Genome-wide association mapping in bread wheat subjected to independent and combined high temperature and drought stress

Abstract

Most investigations to date aiming to identify the genetic basis of the stress response of wheat (Triticum aestivum L.) have focused on the response to single stress agents such as high temperature or drought, even though in the natural situation, these stresses tend often to occur together. Here, a panel of 108 spring type bread wheat cultivars was phenotyped for 15 yield and yield related traits for two years (2014/15 and 2015/16) under non-stressed conditions, under high temperature stress, under drought and under a combined high temperature and drought regime. The mean loss in grain yield caused by all stress regimes was 51.33%. Analysis of variance (ANOVA) of yield trait showed significant differences among genotypes environments and their interactions (G×E). All the studied traits had higher heritability values which ranged from 0.35–0.94 under [C], 0.58–0.95 under [D], 0.62–0.93 under [H] and 0.60–0.95 under [HD]. GWAS was performed by using 9,646 informative SNP markers and based on these polymorphic SNPs population structure analysis divided whole germplasm into five major sub-populations. Mixed model association analysis detected 503 marker-trait associations (MTAs) at P ≤0.001 while 329 MTAs crossed FDR ≤ 0.05 for all traits with phenotypic variances (R2) ranged from 24.83% to 12.51%. Seven new pleiotropic SNPs on chromosome 7D and IAAV8258 (86.91cM) and wsnp_Ex_c7168_12311649 (57.93cM) on chromosome 5A were most stable association in present study. Furthermore, candidate genes Psy and Sr25 (TG0040) were also significant in present study, these genes were previously mapped on 7A and 7D. The region on 7D was assiociated with 7DL.7Ag translocation from Lophopyrum carring rust resistance Yr16 and many other genes. Similarly region on chromosome 7A which was associated with Psy gene was linked with grain yellow pigment content QTLs. Favourable alleles controlling grain yield were of vital importance and incorporation of these alleles after validation through marker assisted selection and fine mapping could be helpful in wheat yield improvement stress and non-stress conditions.

Novel Alleles for Combined Drought and Heat Stress Tolerance in Wheat

“…Grain number was mostly increased by the same allele as grain weight in both GWAS and NILs, indicating an important factor under post-anthesis drought and heat stress. Grain number is known to be affected by pre-anthesis stress (Fabian et al, 2019) but has also been found to be decreased by postanthesis stress (Prasad et al, 2011;Qaseem et al, 2018). Grain number, in our experiments, accounted for only well-filled grains Alleles for Drought and Heat Tolerance in Wheat (i.e., grains of size > 2.0 mm).…”

“…Ten of the 16 identified QTL for grain weight corresponded to QTL identified by Sun et al (2017), of which two, located on chromosomes 1A and 7A, regulated grain weight per spike. Six other QTL associated with grain weight were detected under well-watered, rainfed, or heat conditions Valluru et al, 2017;Wang et al, 2017;Qaseem et al, 2018) and coincided with the QTL for grain weight under DH and the heat response under drought on chromosome 3B, 5B, and the long arm of chromosome 6B (QGWp.adh-3B.1, QGWp.adh-3B.2, QGWp.adh-5B, QGWt.ara-6B.7, QGWp.ara-6B.3). The QTL on the long arm of chromosome 6B also co-located with QTL for harvest index under combined drought and heat stress (Garcia et al, 2019) as well as single grain weight and leaf chlorophyll content under heat (Shirdelmoghanloo et al, 2016).…”

“…The QTL on the long arm of chromosome 6B also co-located with QTL for harvest index under combined drought and heat stress (Garcia et al, 2019) as well as single grain weight and leaf chlorophyll content under heat (Shirdelmoghanloo et al, 2016). Regions on chromosome 3B co-located with QTL for tiller number under combined drought and heat stress, grain number, biomass, and harvest index under well-watered conditions (Qaseem et al, 2018), while the region on chromosome 7A coincided with QTL for spike length and water-soluble carbohydrates (Gao et al, 2015;Dong et al, 2016;Sun et al, 2017).…”

“…The first genetic studies of wheat under a combination of drought and heat stress under controlled conditions were carried out by Aprile et al (2013) in durum wheat and by Qaseem et al (2018) in bread wheat. Experiments in pots under controlled conditions enable a more precise control of the environmental variables and the time of treatment.…”

“…The disadvantage, however, is that results are not always reproducible in the field although they might be suitable for preliminary discovery and for avoiding high costs of field trials (Passioura, 2006;Izanloo et al, 2008). Qaseem et al (2018) identified several QTL under well-watered and heat stressed conditions and one QTL under combined drought and heat stress for grain weight not linked to plant phenology.…”