ASSESSMENT OF HEAT STRESS TOLERANCE USING YIELD-BASED INDICES IN BREAD WHEAT (TRITICUM AESTIVUM L.) GENOTYPES UNDER TIMELY AND LATE SOWN CONDITIONS UNDER DOON VALLEY OF UTTARAKHAND

Abstract

Terminal heat stress is one of the major abiotic constraints limiting wheat productivity under changing climatic conditions. The present investigation was conducted to evaluate 32 bread wheat (Triticum aestivum L.) genotypes under timely sown and late sown environments for identification of heat tolerant genotypes using yield based stress indices and heat map analysis. Significant variation was observed among the genotypes for grain yield and all heat tolerance indices, indicating substantial genetic variability for heat stress tolerance. Grain yield under timely sown conditions ranged from 4.91 to 8.80 g plant⁻¹ with a mean of 6.32 g plant⁻¹, whereas under late sown conditions it ranged from 4.49 to 6.10 g plant⁻¹ with a mean of 5.11 g plant⁻¹, resulting in an overall yield reduction of 19.15% under terminal heat stress. Different stress indices including Stress Tolerance Index (STI), Tolerance Index (TOL), Mean Productivity (MP), Geometric Mean Productivity (GMP), Harmonic Mean (HM), Yield Stability Index (YSI), Stress Susceptibility Percentage Index (SSPI), Relative Stress Index (RSI), Mean Relative Performance (MRP), and Percent Yield Reduction (PYR) were evaluated for identification of stable genotypes. Genotypes HI1634, MP3336, HD3086, GW463, and DBW303 exhibited superior performance under both stress and non-stress conditions and were identified as promising heat tolerant genotypes based on higher STI, GMP, MP, HM, and MRP values coupled with lower TOL and PYR values. Heat map analysis grouped the indices into productivity based and susceptibility based clusters. Productivity indices including STI, GMP, MP, HM, MRP, YI, Yp, and Ys exhibited strong positive association with grain yield under both environments, whereas susceptibility indices such as TOL, SSPI, RSI, and PYR showed negative association with yield stability. The strong correlation among STI, GMP, MP, and HM confirmed their suitability for simultaneous selection of high yielding and heat tolerant genotypes. The study concluded that combined utilization of stress indices along with heat map based correlation analysis is an effective approach for identification of heat tolerant wheat genotypes. The identified superior genotypes may serve as valuable donor parents in future breeding programmes aimed at developing climate resilient wheat cultivars suitable for late sown and terminal heat stress environments.