Comparison of strains of Agrobacterium vitis from grapevine source areas in Australia

Dormant cuttings from grapevine source areas in three Australian states were indexed for the presence of Agrobactenrium vitis, the causal agent of crown gall disease of grapevine. The bacterium was present at varying levels in both rootstock and scion material from New South Wales, Victoria, and Western Australia. A genomic DNA fingerprinting technique was used to compare these strains of A. vitis with strains previously isolated from South Australian propagation material and with strains from the United States of America, particularly strains from the University of California at Davis where a number of Australian grape cultivars originated. Nine distinct DNA fingerprint types were found, demonstrating that A, vitis is a genetically heterogeneous species. There were no DNA fingerprint types in common between Australian states, suggesting that little or no transfer of A. vitis between states has occurred. Two Californian strains were indistinguishable, when analysed by DNA fingerprinting, from strains isolated over a 14 year period in South Australia. This finding is strong circumstantial evidence that A. vitis was introduced to South Australia on grapevine cuttings imported from California. Given the fact that A. vitis is probably not indigenous to Australia, it is possible that the different strains found in each state were the result of independent introductions. Although grapevines from all Australian states tested did contain A. vitis, the existence of unique strains in each state means that the restrictions on movement of grapevine material between states should be maintained, and that quarantine authorities should avoid introducing further strains of the bacterium.