Field-based assessment of sowing date-induced temperature stress on growth, sensitivity, and yield of four cucurbit species

Climate-induced thermal stress is a major constraint limiting cucurbit productivity in subtropical agro-ecosystems. This study quantified the impact of sowing date-induced temperature variations (-0.49°C to +1.9°C) across three regimes - optimal (SD1), late (SD2), and very late (SD3) - on phenological, physiological, biochemical, and yield traits of four Cucurbitaceae species (ridge gourd, sponge gourd, bottle gourd, cucumber) over two seasons (summer-spring and kharif) in field experiments at IARI, New Delhi, India. Climatic suitability analysis indicated that summer-spring crops performed best within a temperature deviation of 0 to 0.95°C deviation, while kharif crops showed optimal performance near 0 to -0.2°C. The composite cucurbit growth index (CCGI) and sensitivity index (SI) revealed species-specific thermal responses, with sponge gourd showing maximum sensitivity during summer-spring and ridge gourd during kharif. Mid-season sowing (SD2) favored greater growth stability, as indicated by higher CCGI (0.466 in summer-spring and 0.388 in kharif). Overall, summer-spring provided more stable productivity (CCGI 0.4325; SI -0.0163) than kharif (CCGI 0.3458; SI -0.0899). These results highlight the utility of integrated indices for assessing crop resilience and identify mid-season sowing as an effective strategy to sustain cucurbit productivity under increasing climate variability.