Abstract
ABSTRACT The biochemical defense mechanisms of amphibians involve cutaneous secretions of bioactive molecules with antimicrobial activity. This study evaluated the in vitro activity of methanolic extracts from cutaneous secretions of two amphibian species of the Bufonidae family, Rhaebo guttatus and Rhinella marina, in the control of the phytopathogens Fusarium udum, Fusarium solani, Colletotrichum truncatum, Aspergillus flavus, Rhizoctonia solani, Macrophomina phaseolina, and Calonectria pseudometrosideri. The R. guttatus extract decreased the mycelial growth of F. udum, F. solani, A. flavus, and M. phaseolina at some tested concentrations. The R. marina extract decreased the mycelial growth of C. truncatum at the concentration of 0.5 mg mL-¹, and inhibited the mycelial growth of A. flavus at concentrations of 0.1 and 0.5 mg mL-¹, which was similar to the inhibition by the positive control. The R. marina extract also decreased the microsclerotia production by R. solani at concentrations of 0.2 and 0.3 mg mL-¹. In addition, the extracts inhibited conidial sporulation and germination at varying degrees. The inhibition of appressoria formation in C. truncatum by the R. guttatus and R. marina extracts was 85-99% and 63-100%, respectively. Our results demonstrated that treatment with extracts from R. guttatus and R. marina cutaneous secretions showed antifungal activity against the studied phytopathogens.
Highlights
The biodiversity of Amazonia is a potential source of chemical compounds of biological and industrial interest (Skirycz et al 2016)
For C. truncatum, we evaluated the emergence of the appressoria in conidial germination assays (Bonaldo et al 2004) and expressed this variable as the appressorial formation inhibition percentage (AFI%) relative to the negative control
mycelial growth (MG) and mycelial growth rate index (MGRI) of F. udum were significantly lower for the 0.5-mg mL-1 concentration relative to the negative control
Summary
The biodiversity of Amazonia is a potential source of chemical compounds of biological and industrial interest (Skirycz et al 2016). Compounds obtained from natural products have shown direct fungitoxic action by inhibiting spore germination and mycelial growth of phytopathogens (Stangarlin et al 2011; Oliveira et al 2014). In this context, the prospection for new active compounds is relevant to overcome pathogen resistance to existing fungicides, which results from the indiscriminate and excessive use of these substances, leading to a feedback cycle of ever higher concentrations of antifungals and a consequent increase in toxic residues in food products (Barros-Velazquez 2016)
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