Origins of kiwifruit disease Psa uncovered

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The bacterial disease that has blighted New Zealand kiwifruit orchards originated in China and was also responsible for an outbreak in Italy and Chile, new research has shown.

Kiwifruit canker, or Psa, has spread to more than 1000 New Zealand orchards since it was discovered in the Bay of Plenty region in November 2010.

Combating the disease was expected to cost between $310 million and $410 million over the next four years - with the long term bill rising to between $740 million and $885 million.

Scientists from the University of Otago's department of biochemistry today published evidence that the bacteria began its journey in China, before travelling to Italy in 2008 and Chile and here in 2010.

This result would help clarify the pathway by which Psa entered New Zealand, researchers Associate Professor Russell Poulter, Professor Iain Lamont and Dr Margi Butler said.

Their research, which involved DNA detective work using advanced genomics technology, appeared today in the international journal PLOS ONE.

To analyse the geographic origin of Psa the researchers sequenced and compared the genomes of Psa strains from Japan, Chile, China, Italy and New Zealand.

Dr Poulter said the team found the core genomes of the Chinese, Chilean, Italian and New Zealand strains were almost identical and likely shared a common ancestor around 10-15 years ago.

However the genome sequence demonstrates that the New Zealand strains are a distinct clone. The Italian strains form another geographical clone.

"These findings paint a clear picture of an independent Chinese origin for both the Italian and the New Zealand outbreaks and suggest the Chilean strains also come from China," Dr Poulter said.