Physiological, Anatomical, and Agronomic Responses of Cucurbita pepo to Exogenously Sprayed Potassium Silicate at Different Concentrations under Varying Water Regimes

Drought is one of the major environmental stresses that devastatingly impact squash development, growth, and productivity. Potassium silicate can attenuate the injuries caused by water stress. Hence, this study was designed to investigate the influence of three concentrations of potassium silicate; 10, 15, and 20 g/L on squash plants versus untreated control under three irrigation regimes; 100, 75, and 50% of estimated crop evapotranspiration (ET). The obtained results indicated that moderate (75% ET) or severe (50% ET) drought stress conditions gradually declined photosynthetic pigments, relative water content (RWC), mineral content, physiological parameters, and anatomical characteristics. These deleterious impacts were reflected on all growth and yield traits, i.e., plant height, fresh and dry weight of root and shoot, and fruit yield. On the other hand, the antioxidant enzyme activities; superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) significantly increased under severe drought stress at 50% ET followed by 75% ET. However, all evaluated exogenous applications of potassium silicate substantially enhanced photosynthetic pigments, RWC, N, P, and K content, antioxidant enzyme activities, and anatomical characters (periderm thickness, cortex thickness, midrib thickness, mesophyll thickness, number of xylem vessels per main vascular bundle, thickness of vascular bundle, thickness of collenchymatous tissue and upper epidermis, and thickness of collenchymatous tissue and lower epidermis). These desirable impacts were reflected in enhancing all growth and yield parameters. Conclusively, this study alludes that the exogenously applied of potassium silicate, particularly at 20 g/L, can alleviate the deleterious effects of drought stress and enhance the growth and productivity of squash plants, especially in arid environments.