Genetic Gain in Wheat for Abiotic Stress Tolerance

Abstract

Wheat (Triticum aestivum) is the world’s most cultivated grain and its production is threatened by many biotic and abiotic factors. Its production can be improved by utilizing genetic diversity in some important traits such as yield and stress tolerance. Characterization of genomic regions underlying adaptation of landraces can show a quantitative genetics framework for local wheat improvement and adaptability. A genomic set of 512 wheat landraces from Iran and Pakistan were genotyped by genotyping-by sequencing. The heterozygosity (H) and minor allele frequency (MAF) of the Iranian wheat landraces (MAF = 0.17, H = 0.005) were slightly lower than Pakistani wheat landraces (MAF = 0.19, H = 0.008), signifying that Pakistani landrace were slightly more genetically diverse. Population structure studies clearly separated the two population, which indicatestwo separate adaptability trajectories. The large-scale data of seven agro-climatic variables (ACV) was relatively dissimilar between Iran and Pakistan shown by the correlation coefficients. Genome-wide association study (GWAS) found 91 and 58 loci associated with ACV’s which possibly pridict local adaptability of the wheat landraces from Iran and Pakistan. By examining the selective sweep, the significant hits were identified on chromosomes A, B, and D (4A, 4B, 6B, 7B, 2D, and 6D) which were colocalized with some known genes related to flowering time and grain size. Another part of this study was the evaluation of genetic gain in morphological, physiological and yield traits for rainfed XIV conditions using twenty-four historic wheat genotypes (cultivars) released from 1911to 2016. Then these cultivars were further tested for G×E interactions by using additive main effect and multiplicative interactions (AMMI) in five environments. A significant increase in grain yield (9.03 kg /ha-year) was noted whereas plant height was decreased over ttime (-0.25 cm per year). The combine analysis of variance (ANOVA-AMMI) explained that the genotype, environment and G×E interaction were extremely significant (P < 0.01) for all traits except relative chlorophyll contents, biomass, maturity date and the number of spikes per plot. The AMMI-ANOVA analysis further showed that the first interaction principal component (IPC) was ghighly significant (P < 0.01) for all the traits. The IPC1 and IPC2 accounted for >40% and >20% of the G×E interaction respectively for all the selected traits. Additionally, the wheat cultivars were evaluated for diversity of important genes like Lr genes, Rh genes, Sr genes by using KASP markers. This research identified the genetic diversity in the wheat landraces and cultivars that can be applied in future wheat breeding programs to achieve targeted wheat production through the development of good quality drought and stress tolerant varieties.