Leveduras como biocontroladoras da queima das folhas do inhame

Abstract

The coastal yam (Dioscorea cayennensis) is a crop of great economic importance, which contributes to the movement of income in the producing states of the Brazilian Northeast. Its high consumption has been influenced by the nutritional and energy value of its tubers. Leaf blight caused by the fungus Curvularia eragrostidis (Henn.) Meyer [teleomorph Cochliobolus eragrostidis Tsuda & Ueyama], greatly limits its production. This disease causes great damage to culture in the Northeast region of Brazil, especially in the states of Paraíba, Pernambuco, Alagoas, Bahia, Maranhão and Sergipe. The pathogen, under favorable conditions of temperature and relative humidity, seriously affects the plantation, causing circular and necrotic spots on the leaves. There are no records of chemical products in the Ministry of Agriculture, Livestock and Supply for the efficient management of this disease. However, fungicides based on triadimenol, mancozeb and tebuconazole are being used but they are not efficient in controlling this phytopathogen due to their production of heterokaryotic mycelia, which makes it essential to look for more effective methods that can replace these products taking into account this low efficiency and environmental contamination. Yeasts are the main inhabitants of the phylloplane and have the potential to compete for space and nutrients. Their use as biological control agents can significantly contribute to the preservation of the environment and the reduction of production loss caused by C. eragrostidis. Given the above, the objective was to evaluate and select yeasts potentially biocontrollers of C. eragrostidis and leaf blight in yam. A pathogenicity test was carried out by spraying spore suspensions of 15 phytopathogen isolates on yam plants with approximately 4 months of growth. The in vitro antagonistic potential of 77 yeasts isolated from yam leaves was evaluated by pairing with a phytopathogen. For in vivo testing, yam plants kept in the greenhouse at approximately 4 months of growth were sprayed to the run-off point where the yeast suspensions were applied four days before spraying the phytopathogen suspensions. Of the 15 phytopathogen isolates used in the pathogenicity test, 14 were pathogenic, highlighting isolates CFS 996, CFS 506 and CFS 985 as the most virulent, and the isolate CFS 996 was selected for in vivo tests. From the antagonism tests performed, the yeast isolates (Y047, Y051, Y052b, Y085 and Y086) were selected for in vivo biocontrol tests due to their higher percentages of inhibition of the mycelial growth of the phytopathogen. Among the five yeast isolates tested in vivo, Y047, Y051 and Y052b were considered biocontrollers of leaf blight in yam, as they efficiently reduce the severity of the disease. This is the first report on the reduction of symptoms of yam leaf blight by the antagonistic activity of yeast isolates, suggesting its use in the management of the disease.