Identification of antagonistic endophytic actinomycetes A-2 and evaluation of its activity against Valsa mali

An endophytic actinomycetes A-2 against Valsa mali was isolated from healthy apple tree branches.The antagonistic spectrum of strain A-2 and its inhibitory activity against the hyphal growth and conidial germination of V.mali were investigated by using plate growth rate,flat confrontation culture and slide method.In addition,the inhibitory activity of strain A-2 against V.mali in detached apple twigs was also determined.The results showed that the inhibition rate of A-2 fermentation supernatant on V.mali could reach more than 90% and it had obvious antifungal activity against V.ambiens and other eight pathogenic fungi.Strain A-2 could induce alteration on hyphae morphology of V.mali,such as deformation and enlargement.Different dilution of strain A-2 fermentation supernatants all showed obvious inhibitory activity against V.mali in detached twigs.The control efficacy was still above 70% when the supernatant was diluted by 500 folds and used before and after inoculation of V.mali.Based on the cultural characteristics,physiological and biochemical properties as well as 16S rDNA sequencing,the strain A-2 was identified as Streptomyces cavourensis.Actinomycets A-2 could be developed new biological pesticide for control of V.mali.