New Antagonistic Strains of Non-Pathogenic Agrobacterium vitis to Control Grapevine Crown Gall.

Graft unions of nursery stock of grapevine ( Vitis vinifera L.) collected in Japan yielded non-pathogenic strains of Agrobacterium. On the basis of classic diagnostic tests, a sequence analysis and a previously reported multiplex PCR method, the non-pathogenic strains ARK-1, ARK-2 and ARK-3 were identified as Agrobacterium vitis. Stems of grapevine seedlings were inoculated with both a cell suspension of seven mixed strains of A. vitis (Ti) as a pathogen and one of a new strain or A. vitis strain VAR03-1, one of the biological control agents against crown gall previously reported, as competitors to assay the suppression of tumour formation caused by the pathogen. In a test with a 1:1 cell ratio of pathogen/nonpathogen, strains ARK-1, ARK-2 and ARK-3 reduced the tumour incidence.. In particular, strain ARK-1 was strongest at inhibiting tumour formation in this study. Strain ARK-1 established populations on roots of grapevine tree rootstock and persisted on roots for a year. ARK-1, ARK-2 and ARK-3 did not produce a halo of inhibition against A. vitis (Ti) strain on YMA medium. Moreover, strain ARK-1 did not reduce tumour incidence on the stems of grapevine when ARK-1 was dead or only culture filtrate was used. This result indicates the possibility that these new strains inhibit grapevine crown gall in planta by a different mechanism other than VAR03-1. In particular, one of the new strains, named ARK-1, was most effective in inhibiting tumour formation on grapevine and appears to be a promising new agent to control grapevine crown gall. [ABSTRACT FROM AUTHOR]