Helping to save the billion-dollar kiwifruit industry

Victoria University researcher Dr David Ackerley is working to combat the PSA disease that has ravaged New Zealand’s $1 billion kiwifruit industry.

PSA was detected in New Zealand in late 2010 and as of October 2011 had affected 369 orchards covering 2,214 hectares. The rate of spread of the bacterium has increased since then, and latest figures from July 2012 report that 1,239 orchards (collectively representing 47 percent of New Zealand’s total kiwifruit hectares) have now been infected with virulent PSA. If unchecked, it is estimated that the PSA epidemic could cost the industry up to $885 million.

Dr Ackerley, from Victoria’s School of Biological Sciences, is working with Seeka, New Zealand’s largest kiwifruit grower, and Professor Iain Lamont and Associate Professor Russell Poulter from the University of Otago, to overcome the disease.

“PSA has been brutal for our kiwifruit industry and gold kiwifruit are particularly susceptible,” says Dr Ackerley.

“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.”

His team is taking two approaches to find a solution to the disease.

“Our first strategy is to test a range of antimicrobial agents, substances that kill or inhibit the growth of microorganisms, to find combinations of compounds that may be suitable for use against PSA in the field,” says Dr Ackerley.

“Kiwifruit crops could potentially be sprayed or injected with these agents in a carefully regulated manner to help limit the spread of the disease.

“Another possible strategy 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, which will dominate the surface of the plant and prevent the disease-causing strain from establishing a beachhead.

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

Dr Ackerley says the work to sequence the genome of PSA will have ongoing benefits.

“Initially, we’re aiming to combat the spread of the bacterium; longer-term efforts may enable us to understand the precise mechanisms that make PSA such a lethal pathogen, and this could guide efforts to breed more resistant kiwifruit crops.”