Soil application of potassium silicate reduces the intensity of downy mildew in bitter gourd (Momordica charantia L.) leaves

Effect of soluble silicon (Si) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora cubensis was tested using three concentrations of liquid potassium silicate (100, 200, 300 mg Si/kg) added to the growing medium containing top soil, compost and sand. Disease severity, plant growth parameters, silicon accumulation on leaves and cuticle-epidermal layer thickness of transverse sections of leaves were measured. Si treated plants exhibited less disease severity than that of control plants and 200 mg Si/kg treatment resulted in highly significant disease suppression (37 - 53% reduction against controls). The suppression of the disease strongly correlated with the Si accumulation in leaves. Cuticle-epidermis thickness was higher in Si- treated leaves (17.2 - 21.3 μm) against non-treated (10.3 - 13.81 μm). Numbers of leaves, flowers or fruits in Si treated plants were significantly higher (p < 0.05) than control plants except in 300 ppm Si level. Structural changes created by Si may at least be partly responsible for reducing the fungal disease severity in bitter gourd leaves