Extratos aquosos de canola e mostarda-da-índia para o manejo do oídio (Erysiphe polygoni) em feijão-de-vagem, em casa de vegetação

Abstract

Intensive use of chemicals in agriculture, despite increasing crop productivity, has generated concern to producers and consumers, as have associated with degradation and contamination of the environment and also contamination of food. Alternative products such as plant extracts in the control of plant diseases, aimed at reducing the use of synthetic fungicides. Among the diseases that affect vegetables, such as green bean, is powdery mildew (Erysiphe polygoni DC.), which can affect the entire shoot. Brassica sp. have proven effective in the management of plant diseases caused by soil borne pathogens and preliminary results have also shown the same effectiveness in controlling powdery mildew. The use of brassicas in the control of plant diseases, it is a natural alternative method and as the plant extracts are cheaper than fungicides. The objective was to evaluate the effect of aqueous extracts of canola (Brassica napus L.) and mustard-of-india (B. juncea L.), obtained by different extraction methods in the management of powdery mildew in green bean, grown in a protected environment. The experiments evaluating the effect of extracts on spore germination, appressorium formation (in vitro) and AUDPC incidence and severity of disease (greenhouse) were in a factorial 5 x 3 (concentration x extraction methods) with five repetitions. Three extraction methods were simple aqueous, maceration and infusion and five concentrations were 0, 3, 6, 9 and 12% of its extract. Also evaluated the phytoalexin synthesis in soybean cotyledons and the metabolic activity of tissue extracts of green bean, through the analysis of total proteins, enzyme phenylalanine ammonia-lyase and peroxidase and phenolic compounds. The concentrations of the aqueous extract of canola and mustard-ofindia more inhibited the germination of conidia and the formation of appressoria E. polygoni, as well as the severity of powdery mildew were 9 and 12%. In general, all methods of preparation of the extracts were effective in controlling powdery mildew, but those who stood out were simple aqueous and macerated. The simple aqueous extracts of canola and mustard -of-india 9%, were both effective in inhibiting spore germination and in controlling the severity of powdery mildew, equaling the commercial fungicide. This behavior shows that there was effect of voléteis compounds fungitoxic action and may have occurred direct effect, with fungistatic action. It may have also been induced resistance through the activation of POX, SOD and PAL enzymes, resulting in the accumulation of phenolic compounds and phytoalexins.