University of Otago biochemist Associate Prof Russell
Poulter is pictured with high-speed genetic sequencing
equipment used to trace the source of PSA in New Zealand.
Photo by Peter McIntosh.
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
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
''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.