Evaluating the physiological responses and identifying stress-tolerance of Akabare chili landraces to individual and combined drought and heat stresses

Akabare chili (Capsicum annuum L.) contributes to Nepalese rural livelihoods but suffers from low productivity due to various abiotic stresses including drought and heat. This study aimed to assess the physiological responses of Akabare chili landraces to heat and drought stress, individually and together, and to identify stress-tolerant genotypes in the early vegetative stage. Selected eight Akabare chili landraces and chili variety ‘Jwala’ were subjected to control (30/22°C day/night) and heat stress (40/32°C) conditions with irrigation, and drought stress (30/22°C) and combined drought-heat stress conditions without irrigation for seven days, followed by a five-day recovery under control condition. Stress-tolerant landraces showed better performance compared to sensitive ones in terms of efficacy of PS II (Fv/Fm), transpiration rate (E), net photosynthetic rate (PN), stomatal conductance (gs), leaf temperature depression (LTD), water use efficiency (WUE), and the ratio of stomata pore area to stomata area (PASA) under stress conditions, resulting in improved biomass. Although all genotypes performed statistically similar under control conditions, their responses Fv/Fm, PN, E, gs, and WUE were significantly reduced under thermal stress, further reduced under drought stress, and severely declined under the combination of both. Total biomass exhibited a 57.48% reduction due to combined stress, followed by drought (37.8%) and heat (21.4%) compared to the control. Among the landraces, C44 showed the most significant gain in biomass (35%), followed by DKT77 (33.48%), while the lowest gain percentage was observed for C64C and PPR77 during the recovery phase (29%). The tolerant landraces also showed a higher percentage of leaf cooling, chlorophyll content, and leaf relative water content with fewer stomata but broader openings of pores. The study identifies potential stress-tolerant Akabare chili landraces and discusses the stress-tolerant physiological mechanisms to develop resilient crop varieties in changing climates.