Kiwis in hunt to eliminate Psa

Last updated 11:28 26/07/2013

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New Zealand scientists are among a team getting closer to developing new ways of breeding kiwifruit that are resistant to the disease Psa.

After analysing the disease's DNA, the scientists have found a single source of the Psa bacterium is responsible for the recent outbreaks of Psa in New Zealand and Italy, as well as earlier outbreaks in Japan and Korea.

They believe the bacterium is likely to originate in Asia, the birthplace of kiwifruit, but the Psa-V strain is a much more-recent off-shoot.

Scientists from Plant & Food Research and Massey University in New Zealand have joined forces in the project with researchers at the Max Planck Institute for Evolutionary Biology in Germany, the University of Basel in Switzerland and the University of Toronto in Canada

Massey University and Max Planck Institute professor Paul Rainey said analysis of the genome of Psa from around the world showed that outbreaks of disease in Japan in the 1980s, Korea in the 1990s, and Italy in 2008 had been caused by different strains sampled from a single-source population.

"The strain responsible for the Italian and subsequent New Zealand outbreaks, Psa-V, has spread rapidly around the world," he said.

"Understanding its evolution provides us with a more complete picture and suggests that new outbreaks are possible from this ancient source. New Zealand and other kiwifruit growing regions need to maintain vigilance to prevent incursions of new strains of the disease."

Plant & Food Research project leader Dr Erik Rikkerink said the genome sequence from the Psa bacterium would support the development of new tools and technologies to control the disease.

"Bacteria living in close proximity routinely swap genes to create new strains, some of which cause disease and others that are benign," he said.

"This swapping means you need to be careful about which genes you use as targets for resistance."

From a global collection of Psa strains a subset of key genes has been identified in all Psa strains, including the virulent strain found in New Zealand.

Rikkerink said the team was using this information at a molecular level to identify new methods to control Psa and to breed the next generation of kiwifruit cultivars with durable resistance to the disease.

This new knowledge, combined with ongoing research, was vital in developing long term solutions to support industry success despite the presence of Psa, he said.

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- The Press

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