Heat tolerance assessment and molecular diversity analysis of wheat (Triticum aestivum L.) genotypes using Heat Susceptibility Index (HSI) and SSR/STS markers

Overview

This study evaluated heat tolerance and genetic diversity across 25 wheat genotypes under four environmental conditions representing timely and late sowing scenarios at two geographic locations during the 2020-21 Rabi season. Heat susceptibility was assessed using the Heat Susceptibility Index, and molecular characterization was conducted using SSR and STS markers to establish population structure and genetic relationships among genotypes.

Methods and approach

Twenty-five wheat genotypes were cultivated at two experimental sites under timely sown (E1, E2) and late sown (E3, E4) conditions using an Alpha Lattice Design with two replications. Heat susceptibility classification was performed via Heat Susceptibility Index calculations. Molecular diversity analysis employed SSR and STS markers to generate similarity coefficients and construct dendrograms using NTSYS-pc software. Environmental conditions at Jalandhar and Karnal represented distinct thermal stress regimes.

Results

Heat tolerance responses demonstrated significant genotype-by-environment interactions. At Jalandhar, nine genotypes exhibited heat tolerance, while eight were classified as susceptible. At Karnal, the tolerant and susceptible classifications differed substantially, with eleven and six genotypes in each category respectively. Four genotypes—HD2967, WH1142, HD3171, and WH1270—demonstrated consistent heat tolerance across both locations, while DBW71, K1317, WH1105, and HI1628 remained consistently susceptible. Molecular analysis revealed similarity coefficients ranging from 0.61 to 0.94 with a mean of 0.77. Four genotype pairs achieved maximum similarity of 0.94. Dendrogram analysis identified four major clusters with further subdivision, indicating substantial genetic diversity within the population.

Implications

The identification of consistently heat-tolerant genotypes across distinct environmental conditions provides germplasm resources for targeted breeding programs. The variable performance of genotypes across locations highlights the importance of multi-location evaluation in breeding strategy development and suggests environment-specific adaptation mechanisms operate within the population.