Insights into the responses of Akabare chili landraces to drought, heat, and their combined stress during pre-flowering and fruiting stages

Drought, heat, and their combined stress have increasingly become common phenomena in horticulture, significantly reducing chili production worldwide. The current study aimed to phenotype Akabare chili landraces (<i>Capsicum</i> spp.) in climate chambers subjected to drought and heat treatments during their early generative stage, focusing on PSII efficacy (F_v/F_m), net photosynthetic rate (<i>P</i> _N), stomatal conductance (<i>g</i> _s), leaf cooling, and biomass production. Six landraces were examined under heat and control conditions at 40/32 °C for 4 days and at 30/22 °C under drought and control conditions followed by a 5-day recovery under control conditions (30/22 °C, irrigated). Two landraces with higher (>0.77) and two with lower (<0.763) F_v/F_m during the stress treatments were later evaluated in the field under 55-day-long drought stress at the fruiting stage. In both treatments, stress-tolerant landraces maintained high F_v/F_m, <i>P</i> _N, and better leaf cooling leading to improved biomass compared to the sensitive landraces. Agro-morpho-physiological responses of the tolerant and sensitive landraces during the early generative stage echoed those during the fruiting stage in the field. A climate chamber experiment revealed a 13.9 % decrease in total biomass under heat stress, a further 21.5 % reduction under drought stress, and a substantial 38.7 % decline under combine stress. In field conditions, drought stress reduced total biomass by 28.1 % and total fruit dry weight by 26.2 %. Tolerant landraces showed higher F_v/F_m, demonstrated better wilting scores, displayed a higher chlorophyll content index (CCI), and accumulated more biomass. This study validated lab-based results through field trials and identified two landraces, C44 and DKT77, as potential stress-tolerant genotypes. It recommends F_v/F_m, <i>P</i> _N, and CCI as physiological markers for the early detection of stress tolerance.