Prevention Effect Of Endophytic Bacteria BS-315 Against Alternaria Mali On Apple

The apple spot leaf drop disease, Alternaria mali Roberts, is a serious disease which decreases the output and quality of apples. This research isolates and screens effective antagonistic endophytic bacteria against this disease and studies the characteristic of the antagonistic strains. The main results are as follows:83 strains of endophytic bacteria were isolated from apple leaves and fruit peels. According to their appearances, 38 strains from apple leaves can be divided into 9 species and 43 strains from apple peels can be divided into 14 species. The quantity of endophytic bacteria separated from apple leaves and fruit peels reaches 1.50×10~2 cfu/g and 1.27×10~2 cfu/g respectively.Strain BS-315 is an endophytic bacteria isolated from apple leaves.The indoor inhibition effect of strain BS-315 against Alternaria mali showed that strain BS-315 had strong inhibition effect on the disease: strain BS-315 has strong antagonism, with a 10 mm inhibition zone, against Alternaria mali. BS-315 fermentation liquid without strains filtrated from BS-315 fermentation liquid with a concentration of 108 cfu/mL has an inhibition effect of 75.43% and 90.12% on the growth of mycelium and germination of spores respectively after being diluted 10 times. When strain BS-315 was used 24 h before inoculation by Alternaria mali, the prevention effect was above 90% at the third day after inoculation.The research of optimum culturing conditions of strain BS-315 showed that cultural time, cultural temperature, pH values of media and oxygen conditions could affect strain quantity. The result indicated that optimum cultural conditions of strain BS-315 are cultural time 48 h, cultural temperature 30℃, 7.0 pH values of media and oxygen conditions of 200 mL/250 mL. The colonizing test showed that strain BS-315 could colonize inside apple leaves and reached the highest amount (103 cfu/g) 3 d after daubing on the apple leaves.The inhibition effect of strain BS-315 can be influenced by environmental factors: at the range of 18℃-33℃,the inhibition effect of strain BS-315 is not changing as the variation of temperature. In this research, we choose 4 fungicides often used in apple leaves and their concentration used in the field. The results showed that azoxystrobin could promote the growth of BS-315, while carbendazim and propiconazole strongly inhibite the growth of BS-315. Therefore BS-315 can not be used in fields until carbendazim and propiconazole were totally decomposed.