[Problem] To provide a non-pathogenic bacterium which exhibits a crown gall disease control effect or an effect of improving a plant seed germination rate steadily in actual crop production fields and can be used as a biological agrochemical or the like. [Solution] The present invention provides: Rhizobium vitis strain ARK-1 (FERM BP-11426), Rhizobium vitis strain ARK-2 (FERM BP-11427) and Rhizobium vitis strain ARK-3 (FERM BP-11428)； a crown gall disease control agent and/or an agent for improving a plant seed germination rate, which is characterized by comprising a cell of at least one bacterium strain selected from the group consisting of the above-mentioned three bacterium strains and/or a culture of the cell as an active ingredient； and a method for controlling crown gall disease and/or a method for improving a plant seed germination rate, which involves a step of bringing the agent into contact with a plant or a plant seed.
