Introduction
Hull-less pumpkin (Cucurbita pepo L.) is considered one of the most valuable medicinal–industrial crops because of its naked, oil-rich seeds, which are widely used in the food, pharmaceutical, nutraceutical, and cosmetic industries. However, the productivity and seed quality of hull-less pumpkin are highly influenced by environmental conditions, particularly water availability and planting date. Increasing water scarcity caused by climate change and the expansion of drought stress in arid and semi-arid regions have become major constraints to sustainable crop production. Therefore, identifying appropriate irrigation strategies together with optimum planting dates is essential for improving water productivity, maintaining yield stability, and enhancing seed quality under limited water resources.
Materials and Methods
A field experiment was carried out in Kerman Province, Iran, using a split-plot arrangement based on a randomized complete block design with three replications. Four irrigation regimes, including 100%, 75%, 50%, and 25% of field capacity, were assigned to the main plots, while three planting dates (April 14, May 5, and May 26) were allocated to the subplots. Standard agronomic practices were uniformly applied throughout the growing season. Growth, physiological, biochemical, and yield-related traits were evaluated, including leaf area index, relative water content, photosynthetic rate, chlorophyll a, chlorophyll b, carotenoid content, proline accumulation, soluble sugar concentration, lipid peroxidation, seed yield and its components, seed oil percentage, and water productivity. The collected data were subjected to analysis of variance according to the split-plot design, and treatment means were compared at the 5% probability level.
Results and Discussion
The results demonstrated that irrigation regime, planting date, and their interaction significantly affected nearly all measured traits. Progressive drought stress significantly decreased leaf area index, relative water content, chlorophyll a and b, carotenoid concentration, photosynthetic rate, seed yield, yield components, seed oil percentage, and water productivity. These reductions indicate that water deficit impaired plant water relations, chloroplast integrity, photosynthetic carbon assimilation, and biomass accumulation, ultimately restricting reproductive growth and seed development. In contrast, drought stress significantly increased proline accumulation, soluble sugar concentration, and lipid peroxidation, demonstrating the activation of osmotic adjustment mechanisms and antioxidant defense responses under water-deficit conditions. Although these physiological adaptations contributed to stress tolerance, they were insufficient to completely offset the adverse effects of severe drought on productivity. Planting date also markedly influenced crop performance. Among the evaluated planting dates, sowing on May 5 consistently produced superior vegetative growth, physiological characteristics, seed yield, and oil accumulation, probably because reproductive growth coincided with more favorable temperature and radiation conditions. The interaction between irrigation regime and planting date highlighted the importance of integrated management practices. The highest seed yield (0.950 kg.ha⁻¹) and seed oil content (44%) were obtained under full irrigation combined with the May 5 planting date, whereas the lowest values (300 kg. ha⁻¹ and 18%, respectively) occurred under severe drought stress (25% of field capacity) with the May 26 planting date. These findings indicate that an appropriate planting date can partially alleviate drought-induced yield losses by improving crop establishment and optimizing environmental conditions during flowering and seed filling.
Conclusion
The present study demonstrated that hull-less pumpkin is highly sensitive to severe drought stress, particularly when irrigation is reduced below 75% of field capacity. Severe water deficit substantially reduced photosynthetic performance, growth, seed yield, oil content, and water productivity while increasing oxidative stress indicators. Nevertheless, moderate deficit irrigation at 75% of field capacity combined with planting on May 5 successfully maintained most physiological traits, yield components, and seed quality while improving water productivity. Therefore, this treatment can be recommended as the most efficient irrigation and planting strategy for sustainable hull-less pumpkin production under the climatic conditions of Kerman Province. These findings provide practical guidance for optimizing irrigation scheduling and planting time to improve resource-use efficiency, maintain economic yield, and enhance crop resilience under increasing water scarcity and changing climatic conditions.