A breakthrough in sequencing the genome of Psa-V is a significant step in the battle to manage the kiwifruit vine disease Psa-V, says Dr David Tanner.

The Zespri general manager of science and innovation says scientists have been working to do this since Psa-V was first discovered in New Zealand in late 2010.

'Scientists have been working on this since Psa arrived in New Zealand and it will allow us to develop tools and technologies to target the bacteria better. The research also provides critical knowledge to help us breed new cultivars that are resistant to any mutation of the bacteria which may come in future.”

An international collaboration of scientists at five organisations - Plant & Food Research and Massey University in New Zealand, Max Planck from the 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.

Professor at both Massey University and the Max Planck Institute for Evolutionary Biology specialising in bacterial evolution, Paul Rainey, says 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.

'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 New Zealand 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.”

Dr Erik Rikkerink, Science Group Leader and project leader at Plant & Food Research, says the genome sequence from the Psa bacterium will 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.

'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.”

David says the genome mapping fills in gaps in the knowledge about Psa-V. This information, along with other developments in the Psa research and development programme, enables Zespri and Kiwifruit Vine Health to develop new angles for research and to go out to the scientific world through open innovation platforms with a series of questions it is seeking answers to.

David says the research brings new hope to the industry, but also reinforces the fact that Pseudomonas syringae bacteria are very adaptable and other forms of it may still arrive in this country.

'Biosecurity remains our biggest risk.”