Climate change is intensifying drought and heat episodes, posing severe risks to crop productivity in Mediterranean horticultural systems. Cucurbit crops, cucumber ( Cucumis sativus ), melon ( C. melo ), watermelon ( Citrullus lanatus ), and pumpkin ( Cucurbita moschata ), are particularly vulnerable; however, their combined stress responses under field conditions remain poorly understood. This study evaluated 36 accessions per species under two field stress conditions: drought (Dro) and combined heat–drought (HeatDro). Physiological traits Relative Water Content (RWC), Nitrogen Balance Index (NBI) and chlorophyll, flavonol, anthocyanin content, and agronomic traits were measured. Both stresses significantly reduced RWC and anthocyanin content, while increasing flavonol content and NBI. Chlorophyll content increased under drought but declined under combined stress, revealing species-specific and time-dependent responses. Melon and watermelon exhibited greater physiological plasticity, whereas cucumber and pumpkin showed more uniform patterns. Correlation analyses identified chlorophyll and NBI as reliable physiological markers for predicting yield and fruit quality under stress. Several genotypes demonstrated superior performance, notably M05 and M17 (melon), S05 and S11 (watermelon), P14 and P64 (cucumber), and CM11 and CM28 (pumpkin), representing valuable resources for resilience breeding. These findings provide the first comparative field-based assessment of cucurbit responses to combined abiotic stress, identify candidate tolerant varieties, and support the integration of physiological screening into breeding strategies aimed at improving drought and heat resilience. • Comparative field evaluation of four cucurbit crops under drought and combined heat–drought stress. • Drought stress reduced leaf relative water content while increasing flavonol accumulation and nitrogen balance index (NBI) across species. • Melon and watermelon exhibited stronger physiological and biochemical responses to stress compared to cucumber and pumpkin. • Chlorophyll content and NBI were significantly correlated with yield and stress resilience. • Tolerant genotypes and key physiological traits were identified for breeding programs aimed at improving stress tolerance in cucurbits.
Flores-León et al. (Fri,) studied this question.