The effects of the Psa virus have crippled New Zealand’s kiwifruit industry, but research efforts are aiding its recovery and providing glimmers of hope for the future of kiwifruit. JUDE BARBACK reports.

A visitor to Te Puke could be under no illusions what the main industry is for the bustling Bay of Plenty town. Kiwifruit are everywhere: on the road safety signs, on the ‘Welcome to Te Puke’ greeting, the giant fruit segment marking the entrance to Kiwifruit 360. Te Puke is synonymous with the furry brown mascot. Over three quarters of New Zealand’s kiwifruit come from the region.

But lurking beneath the vibrant homage to the fruit, is a town reeling from the shock of the Psa disease, which was identified in an orchard on 5th November 2010. Psa has been spreading through the Te Puke region since then, killing vines at a cost to the industry of around $900 million. Around 1250 orchards have been identified with the virus, most in the Te Puke region, with recent news reports confirming the discovery of Psa in Waikato and Coromandel orchards. Just under half of New Zealand’s kiwifruit hectares are on an orchard identified with Psa.

Unsurprisingly, kiwifruit growers have seen tough financial times since their crops were hit by the virus. Before the outbreak of Psa in November 2010, gold kiwifruit orchards were typically worth 400-450 thousand dollars a hectare. Now many orchards are stripped to their bare land price of around $70,000 a hectare, leaving orchard owners in a negative equity position, with no income.

The devastation is palatable in Te Puke. Many have had to make tough decisions about the future of their orchards. Some have ripped up their vines, converting the land to other uses. Most are regrafting the affected gold vines in the hope that the new varieties will be tolerant to Psa. Up to 50 kiwifruit growers are believed to have resorted to more drastic measures of illegally injecting their vines with antibiotics and are now facing the consequences.

Beyond the heartache felt in many Te Puke households, there is the sizeable damage to the economy to be considered. Kiwifruit accounts for 46 per cent of all New Zealand horticultural exports and the industry has a $1 billion price tag, by export value.

What is Psa?

What exactly is this dreadful virus that has played havoc with our economy and the livelihoods of so many people?

Pseudomonas syringae pv. actinidiae is a bacteria that, in a kiwifruit orchard, can exist as an epiphyte – living on plant surfaces without causing high levels of infection – or as an endophyte, living within the vine resulting in severe infection, which can be detected by leaf spotting, cane dieback, and sap oozing from the vines. In extreme cases, the vines will die.

It is believed that Psa is mainly spread by wind and rain, although the finger has been pointed at plant material, footwear, vehicles, and orchard tools as well. Despite the part plants and humans may play in spreading the disease, Psa carries no health risks to humans or animals and does not affect plants other than kiwifruit vines.

Two PSA strains have been identified in New Zealand: Psa-lv (less virulent), which is thought to be relatively benign, and Psa-v (virulent), the more deadly strain.

Psa is not a new phenomenon; many other countries, including Japan, South Korea, Italy, France, Chile, and Portugal are familiar with the devastating effects of the disease.

The Italian form of Psa is nearly identical to that found in New Zealand, in that gold vines appear to be much more susceptible to the virus than green vines.

However, in a sickening turn of events, the downpours that have characterised this winter are thought to have led to Psa finding its way into the green variety, with an increasing number of orchards reporting signs of the virus in green vines.

How did Psa reach New Zealand?

No one can be sure how Psa-v infiltrated New Zealand’s kiwifruit industry. An independent report commissioned by the Ministry for Primary Industries failed to reveal how Psa reached New Zealand. However, the report identified biosecurity shortcomings that may point to an answer. In mid-2009, an illegal consignment of kiwifruit plants called Anthers arrived in New Zealand from China, followed by another package from China containing pollen in mid-2010, just four months before Psa was detected in a Te Puke orchard.

According to a ONE News report on the possible cause of the outbreak, both shipments were delivered to a pollen importing company based in Te Puke, and the first discovery of Psa was made in an orchard situated across the road from where the company’s owners live. While the Anthers were discarded, the pollen from the second package was retrieved and tested positive for Psa.

Path to recovery

Regardless of how Psa found its way into our kiwifruit vines, there is an ongoing commitment to combating the disease.

A united research effort between Seeka, New Zealand’s largest kiwifruit grower, and Victoria and Otago universities, is well underway.

The team, including Dr David Ackerley from Victoria, and Professor Iain Lamont and Associate Professor Russell Poulter from Otago, 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 compounds that may be suitable for use against Psa in the field,” says 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.”

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.”

The research is funded by a Technology Transfer Voucher worth potentially up to $1 million over three years from the Ministry of Science and Innovation. The Ministry provides half the funding, with the other half funded by Seeka.

The ZESPRI/Kiwifruit Vine Health Psa Research and Development Programme includes projects, which draw on the expertise of around 20 global researchers to find solutions to Psa. The programme, overseen by a committee of global experts, has been split into six streams: detecting Psa, understanding Psa, controlling Psa, breeding tolerance and resistance, resource development, and impacts on New Zealand kiwifruit supply chain.

Under each stream, there are numerous projects at various stages of completion. Most are conducted by research institutes like Plant & Food Research, Hills Laboratories, and universities from around the world. Not surprisingly, the bulk of the projects fall into the ‘controlling Psa’ stream, which is one of the most significant issues confronting the industry.

There is also a product testing programme underway in which a range of products are tested to measure their effectiveness in controlling the spread of Psa-v.

Plant & Food Research have been the driving force behind the research. Since November 2010, the organisation has invested over $1.5 million in Psa response work and expects to spend a further $5 million in the next financial year.

The most recent developments involve the introduction of new varieties of gold kiwifruit that exhibit greater tolerance to Psa. New varieties G3 and G14 appear to be showing tolerance, and there is also some hope for an Enza/Turners & Growers cultivar known as A19 or EnzaGold.

In June this year, ZESPRI released over 2000 hectares of Gold3 license allocation, in order to give growers the opportunity to transition their orchards.

Initially industry leaders held high hopes for the new varieties. Among them, Kiwifruit Vine Health chief executive, Barry O’Neil, who described the release of G3 as “an important development in the recovery pathway”.

“It does not take Psa-V out of the picture, but it does give growers the opportunity to better position orchards for the long-term in a Psa-V environment,” said O’Neil at the time.

“This Gold3 variety has been growing for a few years now, and we already know it’s considerably more tolerant to the Psa disease than the existing variety is, so we have reasonable confidence that this new variety will work,” said New Zealand Kiwifruit Growers Incorporated (NZKGI) president, Neil Trebilco in a statement released in June

However, despite the hopes of industry leaders pegged on the greater resistance of new kiwifruit varieties to Psa, symptoms of the disease have been found in both newly grafted and more mature G3 vines just before harvest this year. While not wholly unexpected, this discovery, coupled with the penetration of Psa into green varieties and into new regions, comes as an unwelcome blow to an industry desperately struggling to find its feet.

It is apparent there is no quick fix solution here; there is a long road ahead for kiwifruit growers. It is encouraging to see the investment in research programmes geared up to understand more about Psa, how to control it and ultimately help New Zealand’s kiwifruit industry recover.

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