MITIGATION EFFECTS OF SILICON ON TOMATO PLANTS BEARING FRUIT GROWN AT HIGH BORON LEVELS

Abstract

Interactive effects of silicon (Si) and high boron (B) on growth and yield of tomato (Lycopercison esculentum cv. '191 F1') plants were studied. Treatments were: 1) control (B1), normal nutrient solution including 0.5 mg L-1 B (boron), 2) B1 + Si treatment: 0.5 mg L-1 boron plus 2 mM Si, 3) B2 treatment: 3.5 mg L-1 B, 4) B2 + Si treatment: 3.5 mg L-1 B plus 2 mM Si, 5) B3 treatment: 6.5 mg L-1 B, and 6) B3 + Si: 6.5 mg L-1 B plus 2 mM Si. High B reduced dry matter, fruit yield and chlorophyll (Chl) in tomato plants compared to the control treatment, but increased the proline accumulation. Supplementary Si overcame the deleterious effects of high B on plant dry matter, fruit yield and chlorophyll concentrations. High B treatments increased the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1). However, supplementary Si in the nutrient solution containing high B reduced SOD and PPO activities in leaves, but POD activity remained unchanged. These data suggest that excess B-induced oxidative stress and alterations in the antioxidant enzymes. Boron (B) concentrations increased in leaves and roots in the elevated B treatment as compared to the control treatment. Concentrations of calcium (Ca) and potassium (K) were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplementing the nutrient solution containing high B with 2 mM Si increased both nutrients in the leaves. These results indicate that supplementary Si can mitigate the adverse effects of high B on fruit yield and whole plant biomass in tomato plants.