Soybean rust, caused by Phakopsora pachyrhizi, has been controlled by fungicide application due to the absence of resistant cultivars. Silicon (Si) has increased the resistance of many plant species to pathogens. Therefore, this study evaluated the effect of foliar application of this element on rust severity and if it can potentiate the activity of chitinases, β-1,3-glucanases, peroxidases, polyphenoloxidases, lipoxygenases, and phenylalanine ammonia-lyases. Soybean plants (cultivar "MG/BR-46 Conquista") were sprayed with water (control), potassium silicate (KSi) (pH 10.5), KSi (pH 5.5), and acibenzolar-S-methyl (ASM) 24 hours before inoculation. There was no significant difference among the treatments for content of Si and potassium in leaf tissue. Rust severity was significantly lower on plants sprayed with KSi, regardless of pH, and ASM compared to plants from control treatment. The ASM significantly decreased severity by 65.5% in comparison to control; however, there was no significant difference from ASM to KSi pH 5.5 treatment. Application of KSi, regardless of the pH, also reduced severity. There was no potentiation of the enzymes studied with KSi, regardless of pH and of ASM, even though there was severity reduction compared to the control treatment. This could be explained by the possible effect of these products on the fungus.
Phakopsora pachyrhizi; mechanism of host defense; mineral nutrition
