Insight into inducing disease resistance with Allorhizobium vitis strain ARK-1, a biological control agent against grapevine crown gall disease

The nonpathogenic strain ARK-1 of Allorhizobium vitis has an antagonistic activity toward the tumorigenic (Ti) strain of A. vitis and works as a biocontrol agent, but the biocontrol mechanism in plants needs to be better understood. Inoculations of ARK-1 or Ti strain induced expression of marker genes for defense-related phytohormones such as salicylic acid, jasmonic acid, and ethylene in grapevine within 72 h post-inoculation (hpi). Inoculation of Ti strain 5 days after ARK-1 pre-inoculation induced expression of the marker genes except for the LOX-9 gene in a similar manner to those without the pre-inoculation, suggesting that ARK-1 did not induce typical acquired systemic resistance. However, the transcript of LOX-9 was detected at 24 and 48 hpi with Ti strain when ARK-1 was pre-inoculated, unlike the uninoculated condition. ARK-1 primed the induction of certain defense genes, and it may take part in its biocontrol activity.