Genetic Studies for Heat Tolerance in Cotton: Screening, Correlations and Molecular Validation

Background: Climate change-induced heat stress significantly threatens cotton (Gossypium hirsutum L.) production in Pakistan, where temperatures frequently exceed optimal ranges during critical reproductive stages. Identifying heat-tolerant genotypes is crucial for sustainable cotton production under changing climatic conditions. Methods: Thirteen cotton genotypes were evaluated under controlled conditions with two treatments: normal (35-40°C) and heat stress (45-50°C). Data were recorded for eleven morpho-physiological traits including sympodial branches, boll shedding, mature bolls, plant height, and water content parameters. Molecular validation was performed using five heat shock protein (HSP) primers (G HSP-26, HSP-CB, HSC-71, HSP-101, HSP-3) on four selected genotypes (two tolerant and two susceptible). Results: Analysis of variance revealed significant (p<0.001) genetic variability among genotypes for all traits. Genotype × environment interaction was significant for key traits including fresh leaf weight (1.18) and turgid leaf weight (1.73). Under heat stress, genotypes SS-102, Cyto-537, Cyto-178, and FH-333 demonstrated superior performance across multiple traits. Correlation analysis revealed significant positive associations between sympodial branches, plant height, and number of nodes under both conditions. Molecular analysis showed differential expression of HSP genes, with HSP-3 being downregulated in heat-susceptible genotypes. Conclusion: The study identified SS-102, Cyto-537, Cyto-178, and FH-333 as heat-tolerant genotypes based on morpho-physiological performance. These genotypes showed better adaptation through maintained physiological functions and differential HSP gene expression under heat stress. The identified genotypes and molecular markers provide valuable resources for breeding heat-tolerant cotton varieties.