Bacillus velezensis JK-XZ8 prevents and controls crown gall disease on Prunus subhirtella by colonizing and inducing resistance

Crown gall of Prunus subhirtella Miq.,flowering cherry,is a soil-borne bacterial disease caused by Agrobacterium tumefaciens Smith & Townsend and has caused serious damage to the species in recent years in China.In this study,the colonization of sapling roots,the biocontrol efficacy,the expression of defense-related genes and the enzyme activity in roots of P.subhirtella inoculated with the Bacillus velezensis JK-XZ8 against A.tumefaciens were determined under greenhouse conditions.The results showed that the JK-XZ8 strain colonized in the rhizosphere and root surfaces of the saplings.Sole application of the strain increased activities of polyphenol oxidase(PPO) and phenylalanine ammonia lyase(PAL) without affecting superoxide dismutase(SOD).SOD and PPO activities increased in the prevention group,and the activity of PAL increased in both the prevention and cure groups.The expression of the defense-related genes PAL and PR-1 of salicylic acid pathway in roots increased in both the prevention and cure groups.Simultaneously on day 3,the expression of both COI and MYC2 genes of the jasmonic acid pathway significantly increased in the two groups.The incidence of crown gall in the prevention and the cure groups were 48.1% and 66.7%,respectively,significantly lower compared to the pathogens alone(87.5%).This study showed that the application of the JK-XZ8 strain reduced the incidence of crown gall in P.subhirtella saplings in the two groups,and the prevention group had better control efficacy.In addition,the JK-XZ8 strain protects against crown gall by developing induced systemic resistance and systemic acquired resistance in the roots of the cherry saplings.