Kiwifruit – learning to live with Psa
In November 2010, the bacterium Pseudomonas syringae pv. Actinidiae (Psa) was discovered in a Te Puke kiwifruit orchard. Psa had previously decimated kiwifruit crops in other parts of the world. The race was on to confirm whether the Te Puke orchard was an isolated case or whether the vine-killing disease had established itself in New Zealand.
Kiwifruit vine with dieback
A kiwifruit vine shows symptoms caused by the Psa-V disease – leaf spotting and cane collapse.
Kiwifruit – an iconic and valuable product
Although China is the original home – and, in 2018, the largest global producer of kiwifruit – New Zealand is where the fruit was first commercially planted. We began exporting Chinese gooseberries in the 1950s at the height of the Cold War. Fruit exporters Turners and Growers decided to give the fruit a more marketable name, and the iconic kiwifruit was born. In the next few decades, many other countries also began to grow this fuzzy fruit.
Kiwifruit is a big earner for New Zealand. In 2010, the billion dollar industry accounted for 2.5% of the country’s exports, so when the bacterial disease was confirmed on 9 November 2010, there was widespread concern. Italian orchards had been wiped out by the disease in 2008, so growers and exporters were aware of the damage Psa could cause.
Psa has no risks associated with human or animal health or plants other than kiwifruit vines. When the disease was announced, some countries immediately restricted imports of the nursery stock, but fruit exports were not affected.
Kiwifruit and Psa – a timeline
- Chronology of events
- Nature of science
Psa in Japan
Kiwifruit Vine Health (KVH)
Psa symptoms first appear on green kiwifruit growing in Japan.
Psa in Italy
Psa is identified in kiwifruit orchards in northern Italy. Outbreaks remain sporadic for several years.
Italian kiwifruit industry decimated
In 2007/08, conditions are ideal for the spread of Psa. Kiwifruit in the region of Lazio are decimated, including a New Zealand-owned orchard. Cost estimates for the Italian outbreak are €2 million (NZ$3.5 million).
Psa detected in New Zealand
University of Waikato
Psa is first detected on a Te Puke orchard. Technical experts from the Ministry of Agriculture and Forestry, Plant & Food Research and Zespri visit the area to confirm the disease. The orchard is quarantined.
Need for evidence
Collecting data is integral to scientific research. Experts visit orchards to collect samples in order to identify the disease affecting the kiwifruit vines. The data (evidence) confirms it is Psa.
75 orchards showing possible symptoms
The Ministry of Agriculture and Forestry begins to check other kiwifruit-growing regions for Psa symptoms. Scientists complete tests to determine what strain of Psa is present. Testing eventually shows that New Zealand has two strains: biovar 3 (highly virulent Psa-V, especially to Hort16A cultivar) and biovar 4 (less virulent Psa-LV).
Data is not always straightforward
Initial data was confusing as it appeared that Psa has spread all over the country. Scientists have to analyse and interpret the data to explain why the disease is in so many areas.
South Island cases confirmed
Motueka and Golden Bay confirm cases of Psa. Experts suspect that Psa has been in the country for some time, but a severe weather event stressed vines, allowing the disease to take hold.
Containment strategies
University of Waikato
Industry, government and science agencies try several strategies to contain the disease. Infected vine cuttings are destroyed in huge incinerators or by burial in deep pits. Copper sprays and other chemical solutions are trialled. Movement between orchards is controlled, and equipment is disinfected.
When filming at a kiwifruit orchard the Science Learning Hub crew had to wear protective clothing to reduce the risk of PSA spread.
Using prior evidence
Science and industry use existing information to try and prevent the spread of the disease. Science knowledge often represents the best explanation at the time but can be revised if warranted by new evidence.
Kiwifruit Vine Health is established
Kiwifruit Vine Health (KVH) is established to lead the industry response to Psa-V. KVH holds numerous research and development update meetings featuring the latest scientific and industry information.
Shared purpose
Scientific investigations often bring people from a range of experiences together. Industry and science join together to share information and keep the public informed.
Psa-V spreads in New Zealand
Psa-V is now identified in 369 orchards covering 2,214 hectares.
Significant funding for investigations
University of Waikato
Plant & Food Research (PFR) has a large team of 100+ people working on the development of Psa-tolerant and resistant cultivars. PFR, Zespri and Kiwifruit Vine Health invest more than $11.5 million in research.
Gold3 identified as Psa tolerant
University of Waikato
Gold3, growing in a PFR research orchard, appears to be tolerant to Psa-V. Plant & Food Research fast-tracks commercialisation. More than 2,000 ha of Gold3 plants are released to growers.
Image: Zespri® SunGold kiwifruit. University of Waikato.
Society and science funding
Science exists within and is influenced by the needs of society. Primary industries like horticulture are valuable to the New Zealand economy. Societal needs often influence where and how science funds are allocated.
Making predictions
In science, a prediction is an expectation that a hypothesis is correct. Scientists usually prefer to have sufficient evidence to support a hypothesis, but some situations require more urgent action.
More orchards are infected
12,000+ New Zealand kiwifruit orchards are infected with the virulent form Psa-V – nearly 40% of the country’s orchards.
National Psa-V Pest Management Plan
Minister for Primary Industries Nathan Guy approves a National Psa-V Pest Management Plan (NPMP). The plan ensures the entire industry works together to overcome the impacts of Psa-V. Grower levies fund the NPMP.
Psa bacteria origins
Plant & Food Research
An international collaboration discovers that a single source of the Psa bacterium is responsible for the recent outbreaks of Psa in New Zealand, Italy, Japan and Korea. They report that the Psa bacterium most likely has its origins in Asia. However, the Psa-V strain is a much more recent offshoot.
Building knowledge
Scientists seek to build knowledge about the natural world. Researchers from New Zealand, Germany, Switzerland and Canada combine new molecular knowledge with existing knowledge to develop long-term solutions for Psa-resistant cultivars.
Crowdsourcing knowledge
Plant & Food Research scientists share kiwifruit and Psa bacterium genome sequences for global collaboration. They invite the international science community to help solve the problems facing kiwifruit growers across the world.
Collaboration and sharing ideas
Scientists rarely work alone. Most research takes too long, is too expensive and needs more knowledge and expertise than one person or even a small team may have.
Biocontrol microorganisms
A consortium of New Zealand experts investigate biological control agents (BCAs) that can significantly resist Psa symptoms in kiwifruit vines. Two BCAs are applied to the leaves. One BCA is a root-dwelling beneficial fungus.
Tentative nature of science
Working on multiple solutions offers opportunities for trial and error. Ideas may fail before more successful measures are discovered. This is an important part of the research process. The scientific process presents both challenges and promising results.
Partnering with China
Plant & Food Research
New Zealand scientists partner with China to identify new sources of resistance to kiwifruit pests and diseases. Research leader Dr Mirco Montefiori notes, “We have a large kiwifruit germplasm collection in New Zealand, but the diversity of kiwifruit vines in China is virtually endless.”
Scientific research is an ongoing activity
Most scientific research is rarely considered ‘finished’. Even though Psa appears to be manageable in New Zealand, scientists continue to look for answers.
From $2.6 billion to $6.14 billion
The kiwifruit industry continues to recover. A University of Waikato report suggests the kiwifruit industry will increase its contribution to New Zealand’s GDP from $2.16 billion in 2015/16 to $6.14 billion in 2030.
Prime Minister’s Science Prize
Prime Minister’s Science Prizes Secretariat
Plant & Food Research receives the 2017 Prime Minister’s Science Prize and will use the $400,000 prize to support bioprotection technologies.
Image: Prime Minister Jacinda Ardern with Dr Bruce Campbell, Plant & Food Research Psa Team Leader.
Contributing to society
Science has significant impact on our physical, social, economic and environmental health and wellbeing – as demonstrated by the rapid and effective response of the Plant & Food Research team to the Psa crisis.
Living with Psa-V
Kiwifruit Vine Health reports that 2,949 orchards are identified as having Psa-V. This represents 92% of New Zealand’s kiwifruit hectares. Growers live with Psa but have a toolbox for managing the disease.
High Court rules in favour of kiwifruit growers
Rafael Ben-Ari, 123RF Ltd
The New Zealand High Court rules that the Ministry of Agriculture and Forestry – now known as the Ministry for Primary Industries – breached its duty of care by approving a permit to import pollen products into New Zealand. The Crown argues that growers do not have a case as studies regarding how Psa-V entered the country are inconclusive.
Science is a knowledge system
Although scientific research is used as evidence in legal matters, science itself is a knowledge system. Research provides information, which is then acted on by other parties.
Kiwifruit and Psa – a timeline
This timeline follows the discovery of the bacterial disease Psa (Pseudomonas syringae pv. Actinidiae) in New Zealand, the combined efforts to first contain and manage the disease and the research that enabled the kiwifruit industry to make a strong recovery. Find out how this work reflects the nature of science. A full transcript is underneath the timeline.
The question: Can we eradicate the disease?
A rapid response team from the Ministry of Agriculture and Forestry, Plant & Food Research and the marketing company Zespri took samples from the Te Puke region. The worst-affected orchards used copper-based sprays, vine removal and strict orchard hygiene practices. Psa is spread by wind and rain, so the possibility of eradication was slim.
The next step was containment. Researchers investigated antimicrobial agents and orchard management techniques to limit the spread of the disease. Neither of these strategies was successful so the teams moved to investigating ways to control Psa.
Germplasm collection, genetics and the search for new cultivars
Scientists discovered that two variants of Psa were in New Zealand – the highly virulent Psa-V and the less virulent Psa-LV. Psa-V proved to be particularly harmful to many of the country’s existing cultivars, including the lucrative Hort16A, better known as Zespri® Gold .
The kiwifruit industry, Plant & Food Research and other government agencies worked together to find new cultivars with greater resistance to Psa-V. Plant & Food Research scientists sequenced the Psa genome to identify the proteins that overwhelm kiwifruit plant defences. They also screened thousands of cultivars in their germplasm collection for plants that were Psa-V resistant and had desirable traits such as flavour, colour, storage and crop yield.
Zespri® SunGold kiwifruit
This gold kiwifruit cultivar is more resistant to Psa-V. It also has desirable growing and marketing traits.
Fortunately, Plant & Food Research had three new cultivars in pre-commercial trials. The cultivar Gold3 (marketed as Zespri® SunGold) met all of the requirements, and Plant & Food Research accelerated the commercialisation process to allow growers to replace their Hort16A vines with Gold3 vines.
Plant & Food Research and Zespri – Responding to Psa
In 2010 Plant & Food Research and Zespri responded to the Psa outbreak by using their established relationships to assure scientists were quickly deployed to fight the disease.
The response saw the two companies nominated for the Minter Ellison Rudd Watts Research and Business Partnership Award at the KiwiNet Awards 2015.
Operations Manager Bryan Parkes and Business Manager Stuart Kay from Plant & Food Research explain the response to the disease and subsequent outcomes for the kiwifruit industry.
Investment pays off
Plant & Food Research reports that Zespri exported $2.3 billion of kiwifruit in the 2016/17 season – nearly 20% more than the 2008 season before the Psa outbreak. The rapid response of the Plant & Food Research team to the Psa crisis earned them the 2017 Prime Minister’s Science Award. It recognises the immense effort put in by the plant pathologists, breeders, orchard management specialists and others in the 100-strong team.
Psa took the industry to the brink and the industry and the science team have stepped up, and now that industry is pushing toward a $6 billion target in the future.
Dr Bruce Campbell, Chief Operating Officer, Plant & Food Research
Plant & Food Research are quick to give credit to their close association with industry partners in New Zealand and to researchers around the world for the collaborative efforts to achieve a successful result. The teams haven’t finished. Research and development programmes in New Zealand and internationally are still looking for solutions for Psa-V. In the meantime, growers have learned to live with Psa-V and to minimise its impact on their orchards.
Related content
Kiwifruit is actually difficult to pollinate. Read about the issue and some of the ways Plant & Food Research is helping to solve them in the article Kiwifruit pollination problems.
Learn more about germplasm collections in the article The germplasm collection: a library of apples.
Links to news articles and radio interviews from 2010–2012:
The Science Learning Hub team has curated a collection of resources with biosecurity as the context for learning. The collection has notes on how to use this article and timeline to promote and practise understanding of the nature of science. You are welcome to copy the collection to your own profile, where you can edit and curate additional resources. Find out more about our easy to use collection tool.
Useful links
The Kiwifruit Vine Health website has information on Psa-V management.
Use the Plant & Food Research search to see more resources on Psa research.
