Nutrientes minerais ativam respostas de defesa em soja para o manejo do oídio

Abstract

Soybean (Glycine max (L.) Merrill) is a legume belonging to the Fabaceae family and is one of the main agricultural crops in Brazil. Biotic factors, such as the occurrence of fungi, are responsible for causing significant losses in the production of this crop. The fungus Erysiphe diffusa, the etiological agent of soybean powdery mildew, is a biotrophic fungus that can lead to productivity losses ranging from 10 to 35%. The primary control measure for this disease is the application of chemical fungicides. However, the use of mineral elements such as copper is an alternative for controlling this disease, as this element possesses antifungal characteristics and acts in the plant defense system, promoting mechanisms in response to pathogen attacks. In this context, the objective of this study is to evaluate the effects of copper spray applied either alone or in combination with calcium and/or magnesium in managing powdery mildew in soybeans and in the defense responses of the plants. The experiments were conducted in a greenhouse at the Department of Phytopathology, Federal University of Lavras, following randomized block designs (DBC) with four replications. The treatments included a negative control (no application of products), a positive control (commercial fungicide), and six treatments consisting of different combinations of calcium, magnesium, and copper doses. Powdery mildew severity was evaluated based on a diagrammatic scale, as well as plant growth. Plants showing lower disease severity were analyzed for their defense responses, determining the activity of the enzymes phenylalanine ammonia-lyase (PAL), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), quantifying the levels of total soluble phenolic compounds, soluble lignin, chlorophyll A and B, phytoalexin glyceollin, coumestrol, daidzein, genistein, and glycitein. The results indicated that foliar application of 1 kg/ha-1 copper sulfate associated with 0.5 kg/ha GEOX is a promising alternative in the management of soybean powdery mildew. It was also identified that this same dose can act as an elicitor of the complex of antioxidant enzymes (SOD, POD, and CAT) that catalyze reactive oxygen species without causing damage to the development of soybean plants.