Silicon Induces Resistance to Bacterial Blight by Altering the Physiology and Antioxidant Enzyme Activities in Cassava

Abstract

Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam) is a devastating disease limiting cassava production. The potential effect of Si application on the physiological and biochemical mechanisms attributed to Si-mediated resistance of cassava to Xam was evaluated. The optimal concentration of Si in enhancing resistance to CBB without detrimental effects on plant growth was determined using cultivars TME14 and TMS60444 known for their susceptibility to Xam. Varied concentrations of Si (0.7 to 2.1 mM) were administered by watering the plants three times per week before and after Xam inoculation. The optimized Si concentration was used to evaluate the effect of Si supplementation on resistance to CBB disease using eight farmer-preferred cassava cultivars. The population of Xam, cultivar resistance, chlorophyll content, lipid peroxidation, H2O2 content, activity of antioxidant enzymes and total Si content in cassava cultivars were quantified 21 days post inoculation. Silicon concentration of 1.4 mM was optimal in enhancing cassava resistance to Xam. Silicon-treated plants of all cassava cultivars showed significantly (P ≤ 0.05) lower Xam population ranging from 5% to 26.7% compared to non-Si treated control plants. Activities of antioxidant enzymes, malondialdehyde, H2O2 and chlorophyll contents were significantly (P ≤ 0.05) higher in Si treated plants than non-Si treated plants. Silicon accumulation in leaves of Si treated plants was higher compared to non-Si treated control plants.