Preliminary Study on Some Actinomycetes and Evaluation of Their Potential Antagonism against Fungal Pathogens

Aims: Control of microbial pathogens by using antagonistic microorganisms is a promising alternative to chemical fungicides. The objective of the present study was to isolate and characterize soil actinomycetes and to their inhibitory activity against some fungal plant pathogens.
Place and Duration of Study: National Park “El Chico”, Hidalgo State, and Laboratory of the Southeast Unit of CIATEJ, Yucatán, México, between June 2010 and May 2011.
Methodology: Actinomycete species were isolated from six composite soil samples using microbiological standard procedures. All isolates were phenotypically characterized. Antagonistic isolates were selected according to the inhibitory growing of Fusarium sp. and Candida albicans. Afterwards, a new evaluation for the isolates selected was done against Helminthosporium sp., Curvularia sp., and Aspergillus niger. Actinomycetes were identified performing an analysis of the 16S rDNA gene sequence.
Results: 164 actinomycete strains were characterized by morphological and biochemical features. Six of them, inhibited the growth of Fusarium sp. and C. albicans from 5 to 10 mm distance in between the actinomycete´s colony growth border of fungal or yeast. A growing reduction from 50 to 83 % in the in vitro antagonism assays was observed for Helminthosporium sp., Curvularia sp., and Aspergillus niger. Results in disc diffusion assays suggested an inhibitory growing capacity of CACIA-1.46HGO for P. capsici, this behavior could be due to the production of diffusible compounds related to secondary metabolism, hydrolytic enzymes, or both of them. Four antagonistic isolates were identified into Streptomyces genus and one as Microbacterium sp. through 16S rDNA gene sequence.
Conclusion: Actinomycetes could be potentially a control tool to prevent several fungal commercial plants diseases. However, in situ isolate evaluations are suggested to be investigated.