Elicitação em plantas de soja infectadas por oídio: efeitos do metil jasmonato e quitosana em algumas características fisio-metabólicas

Abstract

Soybean has a prominent position in the Brazilian and global agribusiness, characterized as a culture of great socioeconomic importance due to its multiple uses. Pathogenic agent Erysiphe diffusa, which causes powdery mildew, is characterized as a highly aggressive disease, and can significantly limit soybean productivity. The use of resistance inducers for culture protection is a feasible alternative for maximizing plant defense. Among these inducers, we highlight methyl jasmonate (MeJA) and chitosan, which activate the octadecanoid pathway, of which final product is jasmonic acid, a plant hormone that induces the activation of defense mechanisms against pathogen attacks. As external elicitors, they can induce plant resistance, increasing the activity of enzymes related to defense. In order to understand the behavior of induction mediated by these elicitors, this study seeks to elucidate the feasibility of using chitosan, MeJA and their interaction in inducing soybean plant resistance in the presence of E. diffusa. For such, biochemical evaluations were conducted by means of quantifying SOD, CAT, APX, PAL, H2O2 and peroxidation, as well as ecophisiological traits (gas exchange and relative content of chlorophyll) and its relations with disease severity. Under greenhouse conditions, the soybean plants were naturally infected by symptomatic plants, and conducted until the V5 phenological stage, when elicitors MeJA 1.25 mM, chisotan 3 mg/mL, MeJA/chitosan combination and a control with distilled water were applied. At 2, 5, 8 and 11 days after application, the evaluations were performed. Powdery mildew severity was evaluated after the beginning of infection. With the data obtained, we calculated the area under the disease progression curve (AUDPC ). All treatments increased the expression of enzyme activity and levels of H2O2 when compared to the control. The elicitors decreased infection and disease severity. We highlight the effect of the MeJA/chitosan interaction, which delayed the increase of the disease in up to 15 days after application.