Evidence that Bacterial Blight of Kiwifruit, Caused by a Pseudomonas sp., was Introduced into New Zealand From China

Strains of the bacterium, Pseudomonas sp., causing blight of kiwifruit, isolated from affected vines in New Zealand and in the Peopleʹs Republic of China, were compared using DNA-DNA hybridization and repetitive-PCR (rep-PCR) and biolog. DNA of each strain was hybridized to DNA of reference strains representing P. viridiflava, P. savastanoi and the kiwifruit pathogen. Strains of the pathogen from New Zealand and China shared reassociation values exceeding 76%. Strains from both countries shared reassociation values of more than 66% (average 82%) with DNA of the type strain of P. savastanoi, and less than 51% with DNA of P. viridiflava (average 33.5%). A comparison by rep-PCR using the primers REP, ERIC and BOX showed that strains from New Zealand and China were indistinguishable. Comparison of endonuclease restriction patterns of strains from New Zealand showed that those gathered over a 20-year period from different growing regions were more diverse than strains gathered in one orchard in a single season. The ecological implications of these data and the source of the pathogen in New Zealand are discussed. It is concluded that the pathogen originated in China and was introduced into New Zealand in vegetative kiwifruit material, and not as was previously thought, in two small seed samples.