Inhibition of crown gall formation by Agrobacterium radiobacter biovar 3 strains isolated from grapevine

Abstract

Graft unions of nursery stock of grapevine (Vitis vinifera L.) collected in Japan yielded pathogenic and nonpathogenic strains of Agrobacterium. On the basis of classical diagnostic tests, a sequence analysis, and a multiplex polymerase chain reaction method previously reported, the pathogenic strain was identified as Agrobacterium tumefaciens biovar 3, whereas the nonpathogenic strains were assigned to Agrobacterium radiobacter biovar 3. Stems of tomato (Lycopersicon esculentum Mill.) seedlings were inoculated with both A. tumefaciens biovar 3 strain G-Ag-27 as a pathogen and one of the control strains isolated from grapevine or A. radiobacter biovar 2 strain K84 as competitors to assay the suppression of gall formation caused by the pathogen. In a test with a 1 : 1 pathogen/nonpathogen cell ratio, all A. radiobacter biovar 3 strains reduced gall incidence and size compared to that of the positive control inoculated only with the pathogen. Strain VAR03-1 was especially effective in reducing the incidence of gall formation on grapevine and reduced gall size by 84%–100% of those on the positive control. Many tested nonpathogenic biovar 3 strains were bacteriocinogenic, causing an inhibition zone against A. tumefaciens biovar 3 strains on YMA medium. Strain VAR03-1 was the most effective against indicator strains and appears to be a promising agent for controlling crown gall of grapevine.