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.
Highlights
With respect to the volume of production, among the cereals that of wheat is second only to maize
Awn length (AWL), Above ground plant dry weight (Biomass), FLL, Grains per spike (GPS) and PDL were all more strongly compromised by drought, while the number of days to anthesis, to maturity and to heading, as well as grain yield, harvest index, leaf area, plant height, spike length, number of spikelets per spike and number of tillers per plant were more effected by the high temperature stress (Fig 2)
The pleiotropy/linkage of loci contributing both to grain yield and phenology confirms that in stress-prone environment, early maturity is beneficial for grain filling, as it leads to an increase in grain size and yield (S8 Table)
Summary
With respect to the volume of production, among the cereals that of wheat is second only to maize. As a plant adapted to temperate climates, the growth and fertility of wheat are comprised by both high temperature and moisture stress. The effect of the stress is to inhibit photosynthetic electron transport [7]. The plant responses to drought and high temperature stress are commonly assessed in isolation from one another, in nature these two stresses often coincide. Their effect is synergistic [8, 9], altering metabolism and gene expression in ways which are different from what is induced by each stress acting independently [10]. A better understanding of their combined effect will become increasingly important if wheat improvement programs are able to keep pace with climate change
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