Microfungos da Amazônia Meridional : efeito no desenvolvimento de Colletotrichum musae e indução de Fitoalexinas

Abstract

Saprobic conidial fungi (SCF) can act as biocontrol agents of plant diseases, similarly to phytopathogens, can secrete enzymes and produce substances capable of activating plant defense responses. However, unlike the phytopathogens, the SCF ain't capable to cause diseases in plant. The objective of this study was to evaluate the potential of Dictyochaeta sp., Gonytrichum sp., Pseudobotrytis terrestris, Beltrania sp. e Brachysporiella sp. in the induction of phytoalexins in soybean, sorghum and beans, in the “in vitro” control of Colletotrichum musae and in the production of volatile compounds to control banana anthracnose. In the phytoalexin production assays the filtrates were used in dilute solution (50%) and pure solucion, and the phytoalexin production data were expressed as absorbance per gram fresh weight (g.f.w). Was evaluated in the antagonism test mycelial growth, growth rate index, percentage of inhibition of mycelial growth, sporulation and percentage of sporulation inhibition of Colletotrichum musae in direct confrontation with SCF Dictyochaeta sp., Beltrania sp., Gonytrichum sp., Brachysporiella sp., Pseudobotrytis terrestris and Trichoderma asperellum as a positive control. For each treatment against the phytopathogen a note was given according to the scale proposed by Bell after 21 days of incubation. In the test for the production of volatile compounds to control banana anthracnose available the severity of the disease and determination the area under the disease progress curve (AUDPC). There was no phytoalexin production in sorghum and soybeans, however, in the production of gliceolin in soybean, the filtrate of Dictyochaeta sp., pure solution, induced the synthesis of phytoalexin glyceolin in soybean cotyledons. In the d direct confrontation the SCF did not control mycelial growth, rate of growth rate, percentage of growth inhibition and inhibition of sporulation of C. musae, however, considering Bell et al., Beltrania sp. provided better control of the pathogen. Volatile compounds produced by SCF did not control anthracnose in banana fruits, and treatment with Brachysporiella sp. favored the development of the disease. It is concluded that the filtrate of Dictyochaeta sp., pure solution induced the production of glyceolin in soybean cotyledons; Beltrania sp. provided better control of C. musae, suggesting that the antagonist has some mechanism that allows it to obtain nutrient from the pathogen itself and that the volatile compounds produced by Brachysporiella sp. favored the development of anthracnose in banana fruits.