Impact of Water Deficit on Growth and Seed Quality of Cucurbita pepo L. under Separate Selenium and Calcium Applications

Water scarcity is a global issue, and agriculture in Iraq, is one of the most affected sectors by rising temperatures and reduced water availability. Pumpkin (Cucurbita pepo L.) yield, both fruit and seed, is impacted by irrigation deficits and varying water regimes. Therefore, to assess suitability to low water availability, a local cultivar of pumpkin was planted in an experimental farm in Kalar, Iraq. The plants during flowering were exposed to two water regimes: full irrigation to maintain the soil at 100% field capacity (FC) and 50% FC. Selenium and calcium at concentrations of 1.5 mg/L and 5 mg/L, respectively, were applied separately and weekly during the flowering and fruit establishment. A split experiment with a complete randomized block design was implemented with three replicates. Results revealed that selenium application statistically improved the total number of branches, the number of pistillate flowers, and fruit yield per plant compared to the control treatment under 50% FC and 100% FC respectively. Seed traits, including seed weight per fruit, the number of seeds per fruit, the weight of 1000 seeds, and seed yield, enhanced slightly but not significantly when compared with the calcium and control treatments under reduced water usage. Calcium content in seeds increased significantly under 50% FC with the application of selenium and calcium. Similarly, the highest activity of catalase (CAT) and ascorbate peroxidase (APX) enzymes was achieved using calcium in 50% FC. These findings emphasize that selenium demonstrates effectiveness in enhancing certain traits of pumpkin morphology, physiology, and productivity, while calcium was more effective in improving biochemical contents. Further studies are recommended to identify a sustainable and natural alternative to selenium with a similar function and emphasis the role of selenium at the molecular level in pistillate flower development in pumpkin.