Kiwis protecting kiwis from PSA threat

Researchers in New Zealand are working with the kiwifruit industry to combat the PSA (Pseudomonas syringae pv actinidiae) disease that has threatened the $1 billion industry.

Dr David Ackerley from the Victoria University of Wellington is working with New Zealand’s largest kiwifruit grower, Seeka, and Professor Iain Lamont and Associate Professor Russell Poulter from the University of Otago, to find a solution to the spreading disease.

In late 2010, PSA was detected in New Zealand, and by October last year, over 2000 ha of kiwifruit crops were affected. The bacterium continued to spread at an increasing rate.

Dr Ackerley said that the disease has ravaged the industry, with gold kiwifruit being especially susceptible to PSA. “We only have to look overseas to see the potential damage. In the four seasons the PSA bacterium has been in Italy, it has essentially destroyed the gold variety in the country’s main growing area and is now affecting almost every orchard that’s growing green kiwifruit,” he said in a Victoria University report.

The researchers are taking a two-pronged approach to tackling the disease.

“Our first strategy is to test a range of antimicrobial agents - substances that kill or inhibit the growth of microorganisms - to find compounds that may be suitable for use against PSA in the field,” said Dr Ackerley. “Kiwifruit crops could potentially be sprayed or even injected with these agents to help limit the spread of the disease.

“Another possible step is to identify and knock out key genes that make PSA particularly virulent, removing the ‘lethal’ genes that enable PSA to invade kiwifruit vines. You could then inoculate plants with a mild form of PSA that will dominate the surface of the plant and prevent the disease-causing strain from establishing a beachhead.

“This ‘biocontrol’ strategy is particularly exciting to us, and is building off the high-quality PSA genome sequence data generated by our collaborators at Otago.”

While the initial aim of the research is to prevent the bacterium spreading, longer term the findings could result in more resistant kiwifruit crops.