Effects of Silicon on the growth, ion distribution and physiological mechanisms that alleviate oxidative stress induced by powdery mildew infection in pumpkin (Cucurbita pepo, var. Styriac)

Silicon (Si) is considered as one of the beneficial elements for plants that play important roles in plant resistance to stresses. In this experiment, the effects of three levels of silicon (0, 0.85 and 1.7 mM) on the growth and physiological processes of pumpkin were studied in plants inoculated with Sphaerotheca fuliginea (250000 conidia ml−1) and non-inoculated plants under hydroponic condition. Applying silicon increased the Si concentration in plant tissues. Application of Si in plants inoculated with S. fuliginea decreased significantly severity of disease symptom (30%) and also the shoot membrane permeability was decreased. Addition of Si significantly increased the reactive sulfhydryl group content whereas disease decreased sulfhydryl group which was significantly lower in Si-free medium. The infected plants that were treatedwith 1.7 mM Si levels grew and yielded similar to non -infected pumpkins. Using Si nutrition decreased Fe and Mn and increased Zn concentration in the roots and shoots of plants. Alleviation of disease severity in the silicon treatments may be due to enhancing of plant tolerance to disease by decreasing of shoot membrane permeability, increasing the reactive sulfhydryl group content, and also due to effect of silicon on the uptake and distribution of some ions. This study revealed that Silicon at 1.7 mM used in hydroponic system effectively reduced powdery mildew and improved pumpkin growth.