Journal of Plant Pathology Archive

Abstract:

Angular leaf spot, caused by Xanthomonas citri subsp. malvacearum, is the major bacterial disease of cotton in Brazil and other countries. This study evaluated the effectiveness of silicon (Si) for the control of the disease and the possible resistance mechanisms triggered by this element. Calcium silicate (CaSiO3) was incorporated into the soil at concentrations of 0.00, 0.25, 0.50, 1.50 and 3.00 g of SiO2 kg-1 soil 25 days before planting. Leaves of 33-day-old plants were inoculated by infiltration with 0.5 ml of a bacterial suspension (108 CFU ml-1). Components of resistance were evaluated every two days up to 10 days post inoculation, when plant development and the accumulation of Si and calcium were determined. H2O2 production and the activity of enzymes related to plant defenses were analyzed 6, 12 and 24 h post inoculation in +/-Si plants. In vitro inhibition of pathogen growth was also assessed. No significant difference was found among treatments regarding incubation period, disease incidence or bacterial growth inhibition. However, with the application of 1.50 g of SiO2 kg-1 of soil, a reduction in disease severity (54.9%) was observed along an increase in plant height (7%). There was no detectable accumulation of Si in the cotton leaves. In the presence of Si (1.80 g SiO2 kg-1), the level of soluble proteins and the activity of the enzymes SOD, APX, guaiacol- peroxidase, PAL and b-Glu increased, whereas there was a decrease of H2O2. The angular leaf spot reduction observed may be associated with these modification, suggesting resistance induction.