Interactive effects of salinity and water deficit on growth, photosynthetic pigments and oxidative stress responses in pumpkin seed (Cucurbita pepo L.)

Abstract

Increasing soil salinization and water scarcity threaten crop productivity in arid and semi-arid regions. The present study evaluated the physiological and biochemical responses of pumpkin seed (Cucurbita pepo L.) to different salinity and deficit irrigation treatments under greenhouse conditions. Plants were subjected to five irrigation water salinity (S) levels (S1:0.3, S2:2.5, S3:5, S4:7.5 and S5:10 dS m⁻¹) and three irrigation (I) regimes (I100, I75, and I50). Salinity and water deficit significantly reduced evapotranspiration, plant growth, leaf area, and photosynthetic pigment contents. The highest salinity treatment reduced plant height, fresh weight, and total chlorophyll by 57%, 85%, and 69%, respectively. Conversely, oxidative stress indicators, including Malondialdehit (MDA) and hydrogen peroxide (H₂O₂), increased significantly with increasing stress severity. Enhanced proline accumulation and elevated superoxide dismutase (SOD), peroxide (POD), catalase (CAT) activities reflected the activation of osmotic and antioxidant defense mechanisms. The greatest oxidative damage and antioxidant responses were observed under the combined S5I50 treatment, indicating a synergistic effect of salinity and drought stress. Overall, the results suggest that pumpkin plants respond to combined salinity and water deficit through coordinated physiological and biochemical adjustments; however, these mechanisms are insufficient to fully prevent growth suppression under severe stress conditions. These findings provide valuable insights for irrigation management and salinity mitigation strategies in pumpkin cultivation under water-limited environments.