Chitosan induces defensive responses in soybean plants inoculated with Bradyrhizobium elkanii

Abstract

Chitosan is a natural polymer that induces numerous biological responses in many plant species, for instance, the induction of enzymatic and metabolic defense responses to biotic stress. In this paper, basal induced resistance enzymes (β 1-3 Glucanase, Chitinase and Phenylalanine-ammonia-lyase) and protein content, were determined in soybean organs, inoculated with Bradyrhizobium and growth in culture media added with different chitosan concentrations. Defensive response induced by the polymer depended on its concentration, the organ of the plant and the moment evaluated. The behavior of enzyme levels was different in soybean leaves and roots and inversely proportional to protein content. Enzymatic values in leaves were higher at 7 days post-treatment than at 21 days, except β 1-3 glucanase activity. However, in the roots, the increases occurred at 21 days, except chitinase activity. Higher concentrations (100, 500 and 1000 mg L^-1) of chitosan increased the enzyme levels in roots, mainly at 21 days after inoculation with B. elkanii. Results show the possibility of using chitosaccharides for the induction of defensive responses in soybean against pathogens, without affecting the symbiotic process carried out with Bradyrhizobium elkanii.