Changes in the chemical composition of lignin in the leaves of coffee plants supplied with silicon and infected with Hemileia vastatrix
Coffee leaf rust, caused by the fungus Hemileia vastatrix, is considered the main disease of coffee in Brazil. Aiming to find alternatives to control this disease, this study investigated, at the metabolic level, the possible effect of silicon (Si) on coffee resistance to coffee leaf rust. The analytical pyrolysis was used to evaluate possible changes in the chemical composition of lignin on the leaves of coffee plants supplied with Si and inoculated with H. vastatrix. There was no significant increase in the foliar Si concentration for plants supplied with this element, consequently, there was no reduction on coffee leaf rust symptoms. Eight compounds derived from lignin from the p-hidroxifenila precursor (H) were identified, seven from the precursor guaiacyl (G) and one from the precursor syringyl (S) on leaves of plants supplied or non-supplied with Si and non-inoculated or inoculated with H. vastatrix. For the inoculated plants supplied with Si, there was a tendency of occur higher concentrations of the compounds vanillin and caffeine compared to plants non- -supplied with Si and non-inoculated. Plants supplied with Si, regardless of inoculation with H. vastatrix, showed higher values for S/G ratio when compared to non-supplied plants. Even though there was an increase in the concentrations of vanillin and caffeine and higher S/G ration on the leaves of plants supplied with Si and infected with H. vastatrix, this fact did not result in reduction in the symptoms of coffee leaf rust.