Scientists at the University of Otago have succeeded in mapping the genome of the PSA bacteria hitting New Zealand’s kiwifruit orchards – and the breakthrough has already turned conventional thinking about the disease in this country, on its head.
Otago University associate professor of biochemistry, Russell Poulter, says they have discovered that there are not two strains of PSA afterall.
And the more widespread bacteria, previously commonly known just as PSA, is likely to be an indigenous and harmless bacteria.
This has led to scientists renaming it PSD.
“There are two pseudomonas syringae in New Zealand. One of them, PSA, is a virulent pathogen, it’s only recently arrived in the country. It’s within the Bay of Plenty but it hasn’t got out of the Bay of Plenty yet. And you can weigh up the question, well is it still possible to eradicate it?
"The other one, the PS delethiosa, the distantly related thing, has never been found outside of New Zealand by anyone. We actually expect it’s an indigenous bacterium that’s been here for 50 million years since New Zealand broke off from Australia.”
This means that growers in the Hawkes Bay, Motueka and Golden Bay with PSD can rest easy.
“How serious a threat is it to the kiwifruit industry? The answer is no threat whatsoever, it doesn’t cause any harm.”
Seeka chief executive Michael Franks told Country 99TV the science makes a huge difference to kiwifruit growers as it will allow them to identify their priorities.
“We now know there’s only really one which is a bad one, and the significance of that is that it’s reasonably localised in the Bay of Plenty.
"It is spreading like mad, so it is still bad, but the fact is we don’t have more than one PSA floating around in the environment.”
However, Professor Poulter says the virulent PSA-v could still decimate the Bay of Plenty kiwifruit industry – especially the gold variety – as it has done in Italy.
He says had the industry known that there were never two strains of PSA, it may have made a different decision late last year, about whether it was possible to eradicate PSA-v in Bay of Plenty outright.
