One hundred and eighteen strains of endophytic bacteria were isolated from various organs of apple during the growing season through the conventional separation method. The results indicated that the separation probability and the quantity of endophytic bacteria varied with seasons and organs. Strains B86 and B91 with strong antagonistic effect on Alternaria alternata f. sp. mali were screened out through dual-culture and inhibitory activity bioassay. Their fermentation filtrates had significant inhibitory effects upon the pathogen, with the inhibitory rates as 73.72% and 75.32%, respectively. Fermentation filtrates of B86 and B91 in medium had strong inhibition to the spore germination of the pathogen. The deformation and disintegration of the spore germ tubes were observed in the treatment of filtrates. The antifungal compounds of two strains were stable to the heat treatment, indicating that the strains B86 and B91 have the potential biological control function.

biological control; apple; antagonistic endophytic bacteria; Alternaria alternata f. sp. mali