Two novel strains, Bacillus albus JK-XZ3 and B. velezensis JK-XZ8, with activity against Cerasus crown gall disease in Xuzhou, China

In recent years, crown gall of flowering cherry saplings, caused by Agrobacterium tumefaciens, become a serious disease in Xuzhou, China. In this study, the average disease incidence rate in the flowering cherry sapling was 76%, and the disease index was 38. Three-year-old flowering cherry saplings were the most susceptible, and the low-lying terrain was the most favorable condition for the disease. Two strains with distinct antagonistic effects against Agrobacterium tumefaciens were screened simultaneously from the rhizospheric soil of flowering cherry saplings and were named JK-XZ3 and JK-XZ8. The JK-XZ3 and JK-XZ8 strains were identified as Bacillus albus and B. velezensis, respectively, via morphological observation, physiological analysis, biochemical identification and multilocus sequence analysis. The strains JK-XZ3 and JK-XZ8 could effectively prevent the growth of A. tumefaciens. In a greenhouse experiment, the incidence of crown gall in flowering cherry seedlings without the JK-XZ3 and JK-XZ8 treatments was 100%, and the mean diameter of the root nodules was 18.8 mm. The disease incidence in seedlings treated with the JK-XZ3 and JK-XZ8 strains was 16.7% and 22.3%, respectively, and the mean diameter of the root nodules was 6.5 mm and 8.4 mm, respectively. In the field trials, the incidence of crown gall in untreated cherry saplings was 86%, while the incidence of crown gall in saplings treated with the JK-XZ3 and JK-XZ8 strains was 32% and 38%, respectively. These results indicate that the JK-XZ3 and JK-XZ8 strains have a high potential as biological control agents for crown gall of flowering cherry saplings.