Elucidating molecular diversity in spring wheat (Triticum aestivum L. em.Thell.) under terminal heat stress environment using morpho-physiological traits and SSR markers

A set of 36 wheat genotypes was analysed for genetic diversity and terminal heat tolerance under diverse environmental conditions for two years. Based on a minimum mean stress susceptibility index over the seasons, five genotypes, namely, HD3090, HD3086, HD3266, DW1636 and DW1638 emerged as terminal heat tolerant. The D2 analysis grouped the 36 genotypes into eight and six clusters in 2016-17 and 2017-18, respectively. The result of the principal component analysis was also in agreement with the results of hierarchical cluster analysis. Out of 82 SSR markers used to study the molecular diversity, 45 were polymorphic. Estimates for polymorphism information content varied from 0.09 (GWM297) to 0.50 (GWM111 and CFD46), marker index varied from 0.22 (WMC213) to 1.33 (WMC232), and resolving power varied 1.6 (GWM194 and CFD127) to 4.69 (WMC505). A total of 102, including 20 rare and three unique alleles were detected. The number of alleles per marker ranged from 2 to 4 with an average value of 2.2 alleles per marker. Based on SSR polymorphism, the genotypes were grouped into six divergent multi-genotypic clusters. Comparative genotypic grouping using molecular markers and morpho-physiological traits revealed no similarities of genotypic clustering in different crop seasons. However, three out of five genotypes, HD3090, HD3086 and HD3266 identified as terminal heat-tolerant in different clusters based on D2 values and SSR marker cluster analysis. Therefore, these genetically diverse genotypes could be used as a potential donor for improving the terminal heat tolerance in wheat.