Effect of root and foliar applications of silicon on brown spot development in rice

Abstract

Silicon (Si) application is a strategy to manage rice brown spot, but no studies have been conducted on Si as a foliar spray for control of this disease. The purpose of this study was to compare root and foliar Si applications on rice brown spot development, and to determine if there is a biochemical defence response. Rice plants (cv. Metica-1) were grown in a Si-deficient soil that received the following treatments: root application of calcium silicate (CS) (1.25 g/kg of soil), foliar application of potassium silicate (PS) (40 g/L), and control (leaves sprayed with distilled water). Thirty-day-old plants were inoculated with a conidial suspension of Bipolaris oryzae. Si concentration in rice tissue was markedly higher for CS compared with the other treatments. The intensity of Si deposition, as determined by X-ray microanalysis, between the adaxial and abaxial leaf blades of rice plants in the control treatment was similar. Si deposition occurred in both the adaxial and abaxial leaf blades of rice plants that received CS while this Si deposition only occurred on the adaxial leaf blades of plants that received PS. The area under brown spot progress curve (AUBSPC) was not significantly different between the PS and control treatments, but was significantly lower in plants grown in soil amended with CS. The values for the AUBSPC and the number of lesions (NL) per cm2 of leaf area decreased by 37 and 47%, respectively, with CS compared with the control. Conidial germination was not inhibited by PS. The concentration of total soluble phenolics and lignin-thioglycolic acid derivatives was not linked with the reduction observed in the AUBSPC and the NL. Although the concentration of these two biochemical variables seemed to be slightly higher in plants from the control treatment, likely due to the greater disease severity and the NL, rice tissue was not efficiently protected against colonisation by B. oryzae. The results of this study suggest that foliar-applied Si can decrease the intensity of brown spot; however, the level of control achieved was not as great as that obtained when Si was supplied to the roots.