Psa Update 2012

On Friday 5 November 2010, an infection was discovered on a New Zealand kiwifruit vine in Te Puke. Testing confirmed that a bacterium (Pseudomonas syringae pv actinidiae) caused the vine infection.

By March 2011 Psa had been confirmed on 150 orchards. 114 Psa-affected orchards (76% of them) were in the Te Puke region. 40 orchards (less than 2% of the industry) were identified as carrying the Psa-V (virulent) strain. All Psa-V orchards were within the boundary of the Te Puke Psa Priority Zone.

14 GOLD orchards in the Psa Priority Zone were confirmed with secondary symptoms and 45 hectares of Psa-V affected vines were removed (which was less than 0.5% of the industry area).

By March 2012, Psa had been identified in 1094 orchards. 80% of New Zealand’s kiwifruit orchards were in the Priority Zone and 41% of these had been identified with the virulent Psa V strain. Psa V was also found in Rotorua.

The industry seems to have accepted that Psa is here to stay and that the future of Hort16A (the main gold kiwifruit cultivar) is bleak. However there are some apparently tolerant cultivars on the horizon that are currently undergoing rigorous R&D – to assess them for tolerance to Psa and assessments as potential replacements for current susceptible cultivars. New varieties including G3 and G14 appear to be exhibiting field tolerance. There is also an Enza/Turners & Growers cultivar known as A19, or EnzaGold, for which there are also hopes.

Plant & Food Research is running the bulk of Zespri’s R&D on the disease but is also investing in a complementary research programme designed to help the industry.

Since November 2010, Plant & Food Research has invested over $1.5 million in Psa response work. In the coming financial year they expect to spend a further $5 million. The research is being funded chiefly through the reinvestment of royalties that Plant & Food Research earns from the ill-fated ZESPRI™ GOLD Kiwifruit.

The aim is to try and come up with some short-term tools to control the disease, to accelerate medium and longer-term solutions, and build greater Psa tolerance into kiwifruit genetics and new cultivars.

Knowledge from the programme is being shared with ZESPRI and KVH (Kiwifruit Vine Health).

Plant & Food Research is focused on orchard systems and understanding Psa better, so better tools can be developed to control it. Research is currently underway on:

• A full understanding of the biology and lifecycle of Psa.

• Effective and rapid Psa diagnostic tools and crop monitoring systems that allows the industry to make informed management decisions.

• The development of on-orchard management practices that minimise Psa.

• Psa-free pollination systems to enable growers to make informed decisions on pollination in their orchard.

• Identification of the most effective chemical and alternative control approaches to allow growers to confidently manage Psa.

The research covers management within existing orchard systems but is also looking at growing systems that enable the recovery of Psa infected orchards to minimise the impact of Psa into the future.

Research in this area is aimed at rapidly screening the existing kiwifruit material for resistance as well as the longer-term goal of breeding novel resistant cultivars.

The Te Puke Research Station has already identified significant variability in the tolerance of different genotypes to Psa. Business Manager for Kiwifruit at Plant & Food, Stuart Kay, says some are completely resistant, some are totally vulnerable and everything in between.

Plant & Food Research is also utilising its expertise in gene identification and sequencing to rapidly identify Psa resistant genes that can be targeted and selected for use in the new selections.

A lot of hope is being placed on the new ZESPRI and Enza cultivars but plant breeders point out that it isn’t just resistance to Psa that they’re looking for. They also have to have a marketable fruit that works for the grower as well as appealing to the consumer.

Growers say there are going to be a lot of unhappy growers regardless of when and how a new cultivar is released – not everyone is going to get their hands on the plant material and they may not have the right stump area to graft onto.

The industry has also identified the need to come up with systems to make sure budwood and pollen that may be introduced into the orchard in the course of the year can be identified as Psa-free.

There have been suggestions that pollen imported from overseas was a pathway for Psa into NZ. Some are saying that Psa was not on the pollen but on the plant material that came with the pollen. Growers are saying that if this is the case, then biosecurity should be improved so infected plant material can’t get into the country. This is the subject of on-going investigation.

Plant & Food Research is also looking at the long-term impacts of Psa on the supply chain: what is happening once the fruit leaves the orchard gate and heads out to market, and what are the impacts at the packhouse and on further distribution. Dry matter, maturity and storage are other factors that may be being influenced by Psa at the orchard.

Since Psa arrived, grower John Cook has been a lot more hands-on in his orchards. He’s been closely following the progress of the research on Psa. When Rural Delivery first visited him in 2011, growers were looking at spraying and orchard hygiene as important tools along with vine removal in severe cases.

In 2011 John believed the containment programme was working because all of the new outbreaks or the new confirmations of PsaV were still within the priority zone. Unfortunately it proved uncontainable. John was part of an group of affected growers that came together when the disease was first identified in Te Puke. That action group has now morphed into a supply chain/technology transfer group, largely dealing with the supply chain end of the industry.

In general terms, John says there are a lot of growers in debt – having funded expansion when the industry was in good heart and who are now wearing a dramatic drop in cash flow. Some growers are nearing their retirement and are facing trying to rebuild something for themselves, and the next generation. That’s causing a lot of stress and heartache.

He says what growers need now is the release of a resistant cultivar and the right information and technology to get that cultivar grafted onto their orchards. He points out some orchards have literally been leveled and stumps regenerated with suckers…one of his questions is can new plant material be grafted onto them?

Hayward – the green kiwifruit – is the only variety keeping a lot of growers afloat with some kind of meaningful cashflow.

When we first visited BOP to meet people affected by Psa, good orchard hygiene was seen as the key to reducing spread of the disease. Now it is pretty much accepted that spraying vehicles and visitors’ boots is largely a waste of time. Growers have been using copper based sprays but results have been mixed.

Orchardists have also been trialing a range of techniques to see if they can control Psa on the ground. This includes male vine pruning since it appears that the male vines are where infections first appear. Another is girdling which has seen positive results overseas.

Another approach is product testing, currently being undertaken on a range of products that might stimulate the kiwifruit plant and its ability to resist Psa. There have also been trials on steam sterilization for stumps.