A New Zealand scientist has sent a warning to the kiwifruit industry that tolerant varieties could be bowled over by new Psa-V strains if border controls don't improve.

Otago University associate profesor Dr Russell Poulter's team has used DNA sequencing technology with a variety of strains from Italy, New Zealand, Chile, China, Japan and South Korea, as part of Seeka and Eastpak's Taskforce Green initiative.

"When we looked at the Italian strain we found they could be put into a certain group, and New Zealand’s Psa could be classified into a clearly different group," he said.

"The research showed that the strain of Psa in Italy is slightly different to what is in New Zealand, and Chile's strain of Psa-V is also a different strain.

"In this sense you have three separate incursions and none are the same as the others."

Poulter says what this means is that it is unlikely any of these three countries spread Psa to the other, and that the source came from different strains in China where there are multiple types. He adds that the South Korean and Japanese strains were very different as well, so in this sense it could be confirmed there were four seperate incursions outside China.

"What we also did was compare with strains of Psa from China, particularly in Shaanxi as New Zealand imported kiwifruit pollen from there, and we found one particular strain was almost identical to what we have in New Zealand - if you took the label off you wouldn’t know the difference.

"It’s not a question of ambiguity but it is convincingly and obviously true.

"You might say that’s interesting for the sake of history, but who cares? But with this knowledge there are multiple strains in China with very different virulents of Psa, you can avoid for example turning over to a kiwifruit that is tolerant to the New Zealand strain, only to have it knocked over by a different strain."

He says the conclusion is that border control authorities need to work harder so that further cross-contamination does not take place.

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