Morphological, Phytochemical, and Molecular Characterization of Advanced Tomato Lines Under Heat Stress Conditions.

Heat stress severely limits tomato growth, yield, and biochemical stability, highlighting the need for thermotolerant genotypes. This study evaluated six advanced tomato lines using morphological, biochemical, genetic, and molecular analyses under heat stress conditions. Significant genotypic differences (p < 0.001) were observed across the evaluated traits, with TAL101-2 and TAL101-1 exhibiting better growth and reproductive performance under high-temperature conditions. TAL105 showed better growth and antioxidant activity, whereas TAL104 exhibited strong biochemical adaptation, as evidenced by elevated phenolic content and antioxidant activity. TAL101-2 maintained relatively high fruit set despite limited vegetative growth. High heritability and genetic advance for reproductive and phytochemical traits indicated strong genetic control. Correlation and principal component analyses revealed positive relationships between vegetative vigor and yield, whereas biochemical traits were associated with oxidative stress tolerance. Molecular and phylogenetic analyses confirmed clear genetic diversity among the lines. Stress-responsive gene profiling also revealed distinct marker activity patterns. TAL105 and TAL104 were identified as promising candidates for breeding heat-tolerant tomato cultivars.