Isolation and identification of Actinomycetes in soil as biological control agents against plant pathogens

In recent years, the use of microorganisms as a pathogenic antagonist and also a substitute for chemical pesticides is considered. Actinomycetes are one of the most important bacterial groups with the ability to produce a variety of secondary metabolites and could be applied as biological agents against pathogens. This study included isolation, identification and evaluation of antimicrobial activity of Actinomycetes isolated from soil samples against three plant pathogen as Fusarium oxysporum, Xanthomonas campestris and Erwinia amylovora. Actinomycetes strains were isolated on the Starch Casein Agar and Glycerol Casein Agar. The screening of antimicrobial activity against pathogens was primary evaluated with the cross culture method, and followed different seeding and fermentation cultures. Fifteen Actinomycete isolates were selected to measure their antimicrobial activity against pathogens based on their phenotypic characteristics. The primary screening showed that 8 strains have antibacterial effects against at least one pathogen which evaluated by plant pathogen inhibition zone. The results showed that the inhibition zone increases with the use of glycerol medium in some strains. Three strains were identified as Streptomyces sp. based on 16S rRNA gene. The culture compound and conditions optimization of ASC60 strain showed that fermentation media containing glycerol and soy meal at 25°C and neutral pH has the highest inhibitory zone against X.campestris. Future studies can be focused on purification of antimicrobial compounds and improvement of production conditions in order to use effectively these strains in pest control.