Otago research tracks kiwifruit disease to China

University of Otago researchers have proved a canker disease that heavily damaged the New Zealand kiwifruit industry originated in China.

Pseudomonas syringae pv. actinidiae (Psa) has spread to more than 1000 New Zealand orchards since it was discovered in the Bay of Plenty region in November 2010, and long-term costs are estimated at nearly $900 million.

The Otago research provides strong evidence China was the source not only of the Psa outbreak in North Island kiwifruit orchards, but also of the 2008 and 2010 outbreaks in Italy and Chile, respectively. The research, involving advanced genomics technology, has also shed more light on the role of key ''mobile genetic elements'' within Psa.

Researchers say the presence of these elements, which may add to the disease's virulence, underscore the growing importance of strict border control.

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

Assoc Prof Russell Poulter, Prof Iain Lamont and Dr Margi Butler, all of the Otago biochemistry department, undertook the DNA detective work.

Prof Poulter said the researchers were ''really delighted'' with the way their ''internationally significant'' research was progressing.

The researchers had been focusing on mobile genetic elements they had detected in the Psa genome.

These elements - termed ICE or ''integrative conjugative elements''- could transfer between cells of different bacteria strains and alter properties such as their infectiousness and resistance to antibiotics.

Three distinct ICEs had been identified by the Otago team- one was shared by the New Zealand strains, and others linked to Italian and Chilean strains.

Some Psa might be ''inherently more virulent'' because of the particular ICE it carried.

This had ''worrying implications''. Strains of kiwifruit that were resistant to one type of Psa might not be resistant to another.

''This means strict border control by kiwifruit-producing countries is more important than ever,'' Prof Poulter said.

The Otago research also underscored the importance of powerful, multimillion-dollar, genetic sequencing equipment co-ordinated by New Zealand Genomics Ltd (NZGL) and based at the Otago department.

NZGL is a collaborative government-funded initiative, involving Auckland, Massey and Otago Universities.

Prof Poulter said much of the sequencing work had been completed in about two weeks. The task would have been ''impossible''- taking about 1000 years to complete- using equipment previously available in Dunedin.

-john.gibb@odt.co.nz