The Effects of Silicon on Cucumber Plants Grown in Recirculating Nutrient Solution

Abstract

Cucumber plants (Cucumis sativus) cv. Corona were grown in recirculating nutrient solution containing either 10 mg l−1 SiO2 (low Si) which was the level present in the water supply or given an additional 100 mg l−1 SiO2 (high Si). Silicate was depleted from the solution when cucumbers were grown, but accumulated when tomatoes were grown. Major effects on cucumber leaves of added Si were: increased rigidity of the mature leaves which had a rougher texture and were held more horizontally; they were darker green and senescence was delayed. The mature high Si leaves acquired characteristics of leaves grown in a higher light intensity, i.e. they had shorter petioles and an increased fresh weight per unit area, dry weight per unit area, chlorophyll content, RuBPcarboxylase activity and soluble protein (all expressed per unit area of interveinal laminar tissue). Addition of Si did not affect the final leaf area of the mature leaves but root fresh weight and dry weight were increased. A pronounced effect of Si addition was the increased resistance to the powdery mildew fungus Sphaerotheca fuliginea. Despite regular applications of fungicide, outbreaks of the fungal disease occurred on most of the mature leaves on the low Si plants, while the high Si plants remained almost completely free of symptoms. The addition of Si could be beneficial to cucumbers grown in areas where the local water supply is low in this element, especially when grown in recirculating solution or in a medium low in Si, e.g. peat.