Psa family tree gives new tools to breed for resistance

Researching the Psa family tree gives scientists new tools to breed for resistance

Auckland, New Zealand. 26 July 2013…A team of researchers from four countries have analysed the DNA of the kiwifruit disease Psa to identify its origins and develop new ways of breeding for resistance against it.

An international collaboration of scientists at five organisations - Plant & Food Research and Massey University in New Zealand, Max Planck Institute for Evolutionary Biology in Germany, University of Basel in Switzerland and University of Toronto in Canada – has shown that 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.

The research is published in the leading international journal of pathogen biology PLoS Pathogens.

The Psa bacterium is likely to have its ancient origins in Asia, the birthplace of kiwifruit, but the Psa-V strain is a much more recent off-shoot,” says Paul Rainey, one of the collaborators and a Professor at both Massey University and the Max Planck Institute for Evolutionary Biology specialising in bacterial evolution. “Analysis of the genome of Psa from around the world shows that outbreaks of disease in Japan in the 1980s, Korea in the 1990s, and Italy in 2008 have been caused by different strains sampled from a single source population. The strain responsible for the Italian and subsequent NZ outbreaks, Psa-V, has spread rapidly around the world. 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.”

“The genome sequence from the Psa bacterium will support the development of new tools and technologies to control the disease,” says Dr Erik Rikkerink, Science Group Leader and project leader at Plant & Food Research. “Bacteria living in close proximity routinely swap genes to create new strains, some of which cause disease and others that are benign. This swapping means you need to be careful about which genes you use as targets for resistance. From our global collection of strains of Psa we have identified a subset of key genes present in all Psa strains, including the virulent strain found in New Zealand. We are now 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, is therefore vital in developing long term solutions to support industry success despite the presence of Psa.”
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