| The apple spot leaf drop disease, Alternaria alternata f.sp. mali, has become a serious disease in most apple growing areas of China by decreasing the output and quality of apple. The objectives of this research are to isolate and screen effective antagonistic endophytic bacteria against this disease and to study the characteristic of the antagonistic strains. The main results are as follows:One hundred and eighteen strains of endophytic bacteria were isolated from various organs of apple trees and in various growing seasons. The amount of endophytic bacteria separated from leaves is the greatest, reaching 4.95×102 cfu/g, followed by the bark, 4.4×102cfu/g, with the stem in the least, 1.83×102 cfu/g. The endophytic bacteria from leaves accounts for 75%.The result demonstrated that 7 strains of endophytes showed strong antagonistic activities to the pathogen by dual-culture tests, in which strains B86 and B91 had the strongest antagonistic effect through inhibitory activity test. Their fermentation filtrates had inhibitory rates to the pathogen as 73.72% and 75.32%, respectively.Fermentation filtrates of B86 and B91 had strong inhibition to spore germination of the pathogen, with germination rate of 8.7% and 6.7%, respectively. Deformation and disintegration of spore germ tubes were observed in the treatment of filtrates. Two strains had better antagonism to 14 different kinds of pathogenic fungi, indicating that two strains had broader antibiosis range.The antifungal compounds of two strains were stable to the heat treatment between 50℃and 90℃, and between pH5.0 and pH9.0. The rates of inhibition of B86 and B91 were the highest at pH6.0 and pH7.0, but declined when acidity and basicity are respectively strengthened.The results of optimal culture conditions showed that the optimal initial culture pH value of B86 and B91 are pH 6.0 and pH7.0, respectively. The growth of the strains is restrained in strong . The optimal culture temperature of two strains is 28℃and 30℃, respectively. |
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