Suppression effect of two peach rhizobacteria Alcaligenes faecalis on crown gall disease caused by Agrobacterium tumefaciens

【Objective】To screen the antagonists for biological control of crown gall disease.【Methods】Bacteria were isolated from healthy peach roots,stem and rhizosphere soil. Their antagonisms against thecausal agent of crown gall disease,Agrobacterium tumefaciens,were tested by using pair co-culturingmethod. The efficacy of the antagonists in suppressing crown gall disease was further evaluated in green-house using sunflowers and tomato seedlings as susceptible plants. Then the antagonists with strong inhib-itory ability were identified by the analysis of their 16 S r DNA sequences in combination with their mor-phologies and biochemical and physiological characteristics.【Results】A total of 125 bacterial strainswere isolated from the roots,stem and rhizosphere soil of healthy peach trees. Among them,two strains51-A and 51-B produced clear zone around the bacterial colony on the YEB plates inoculated with A. tumefaciens,and five of them grew well without clear zones around the colonies. The ability of strains 51-Aand 51-B to inhibit the crown gall formation was further tested by inoculating the stems of sunflower withcell suspensions of each candidate bacterium and 106 cfu m L-1A. tumefaciens(v∶v=10∶1). After one week growth at 28 ℃ in greenhouse,strains 51-A and 51-B showed good performance in disease control withthe efficacy of 98.0% and 97.0%,respectively. Further test in tomato seedlings by one day pre-drenchingwith antagonistic bacterial cell suspension followed by drenching A. tumefaciens confirmed the suppres-sion ability of 51-A and 51-B against A. tumefaciens with the control efficacy of 91.9% and 86.5%,re-spectively. Strains 51-A and 51-B were then identified to be A. faecalis by their 16 S r DNA sequences incombination with their morphologies and biochemical and physiological characteristics. 【Conclusion】Crown gall disease caused by A. tumefaciens could be effectively suppressed by two peach rhizobacteria A.faecalis which have a great potential for future application in management of crown gall disease.