Identification of heat-tolerant tomato genotypes through integrated phenotypic, biochemical, molecular, and GGE biplot analyses.

High temperature stress is a major constraint affecting tomato productivity and fruit quality worldwide. The present study aimed to identify heat-tolerant tomato genotypes using integrated morphological, biochemical, molecular, and GGE (Genotype plus Genotype-by-Environment) biplot analyses under controlled high temperature stress conditions (40 ± 2 °C, day) compared with optimal conditions (26 ± 2 °C, day). Thirty-five tomato genotypes were evaluated for horticultural, reproductive, biochemical, and molecular traits. Heat stress significantly reduced fruit weight, pollen viability, fruit set, total soluble solids, and yield (g/plant). However, substantial genotypic variation was observed among the evaluated lines. Based on Heat Tolerant Index (HTI), ten genotypes namely VRT-06, VRT-67, Superbug, VRT-494, H-88-78-1, VRT-458, VRT-500, ToDVAR-5, VRT-34, and VRT-613 were identified as highly heat-tolerant. Biochemical analysis demonstrated higher proline accumulation, antioxidant enzyme activities like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), chlorophyll content, and relative water content along with lower malondialdehyde content and electrolyte leakage in tolerant genotypes. GGE biplot and MGIDI (Multi-Trait Genotype-Ideotype Distance Index) analyses identified VRT-06, VRT-67, Superbug, VRT-494, and H-88-78-1 as stable and superior performers across environments. Gene expression analysis revealed significant upregulation of heat-responsive genes (HSP70, HSP90, and HSFA2) and antioxidant defense genes (CAT and SOD1) in tolerant genotypes, particularly VRT-06 and VRT-67, indicating coordinated molecular defense mechanisms under heat stress. Overall, the study identified elite heat-tolerant tomato genotypes and demonstrated the effectiveness of integrating morphological, biochemical, molecular, and multivariate analyses for thermotolerance screening and breeding of climate-resilient tomato cultivars.