Contrasting Heat Stress Responses in Pepper Reveal Targets for Resilient Cultivar Development

Heat stress is a major constraint on pepper (Capsicum annuum L.) production, and the identification of physiological traits associated with heat tolerance is key for developing resilient cultivars. In this study, six genotypes, from the G2P-SOL core collection (www.g2p-sol.eu), were evaluated under progressive heat stress in controlled conditions, with repeated measurements of stomatal conductance (gs), leaf temperature, photosynthetic efficiency (Fv′/Fm′), and leaf water potential. The dynamic response across time points enabled the selection of three genotypes with contrasting behavior. The variety CAP1544 (G2P-SOL code GPC010350), from Croatia, maintained photosynthetic efficiency and stomatal opening, limiting thermal damage and scoring as the most tolerant line in the experiment, while the cultivar “Peza” (code GPC028750), originally from Albania, showed intermediate moderate physiological impairment. Among the six genotypes, CAP446 (code GPC014930), from Costa Rica, appeared to be the most susceptible, exhibiting early stomatal closure, elevated leaf temperature, and reduced water potential. Time-course analyses, combined with multivariate statistics, revealed clear genotype-specific physiological trajectories. Ongoing transcriptomic and biochemical analyses on the selected genotypes will further elucidate the molecular mechanisms underpinning their divergent responses, accelerating the discovery of candidate genes and stress-related metabolic signatures. These contrasting profiles lay the foundation for identifying molecular markers associated with tolerance traits and support their integration into breeding pipelines aimed at improving heat resilience in pepper