Analysis of suppression mechanism of grapevine crown gall disease by nonpathogenic Rhizobium vitis strain ARK-1
K. SAITO (1), M. Watanabe (1), H. Matsui (1), M. Yamamoto (1), Y. Ichinose (1), K. Toyoda (1), A. Kawaguchi (2), Y. Noutoshi (1) (1) Okayama University, Japan; (2) Okayama Prefecture, Japan

Rhizobium vitis is a soil-borne bacteria which causes crown gall disease in grapevine. As a potential biological control agent to counteract this pathogen, a nonpathogenic strain of Rhizobium vitis ARK-1 was isolated. Pretreatment of nursery plants with the ARK-1 strain effectively suppressed crown gall development in not grapevine but also other crops. Co-inoculation of ARK-1 with the tumorigenic (Ti) strain in culture medium resulted in inhibition of the acetosyringone-induced expression of pathogen virulence genes virD2 and virE2. Here we further characterized this antagonistic mechanism. To confirm whether ARK-1 secretes antagonistic substance or not, Ti strain was grown in the filtrated ARK-1-cultured liquid medium with acetosyringone for one day, and the virE2 induction level was assessed. As a result, virE2 expression was reduced clearly. In this condition, we realized that the cell increase of Ti strain was inhibited and this medium also effectively suppressed the growth of nonpathogenic and non-antitumorigenic strain, VAR06-30. Boiling of the filtered-ARK-1 medium cancelled the suppression effects for both virE2 induction and bacterial cell growth. Molecular-weight fractionation experiment revealed that the growth-suppression activity of the ARK-1-cultured medium to Ti strain was in the over 100K fraction. To verify if this substance is directly related to the pest control activity of ARK-1, we are now screening mutants for its growth suppression activity.

Abstract Number: P5-129
Session Type: Poster