The aim of this work was to evaluate the potential of algal polysaccharide ulvan to induce resistance to rust and to study defense mechanisms triggered by it in bean cultivars showing different levels of resistance. Bean cultivars of carioca group, i.e., BR IPA - 11 Brigida (resistant), Perola (moderately susceptible) and IPR Juriti (susceptible), were sprayed with ulvan (10 mg/ mL) or distilled water (control) at 6 and 3 days before inoculation with Uromyces appendiculatus. Ulvan reduced the diameter of pustules on the three cultivars and led to an increase in the activity of glucanases only in cv. Perola, 48 h after inoculation. The polysaccharide did not inhibit the germination of the fungus in leaf discs and did not alter the activity of peroxidases. Comparing the cultivars, Brigida exhibited a significantly lower number and diameter of pustules, but allowed the highest germination of uredospores on the leaf surface. The activities of peroxidases and glucanases were lower in this cultivar compared to the susceptible one (Juriti). Based on the results, we discuss the role of some resistance mechanisms in both basal and ulvan-induced resistance of bean towards the rust fungus.
bean rust; germination; resistance induction; PR-proteins
