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Published: 4 Oct 2022

Professor Calum Wilson in lab

A practical solution for preventing powdery scab disease of potatoes is a step closer, with research moving out of the lab and into the paddock for proof-of-concept testing in Tasmania and New Zealand this season.

Powdery scab is one of the major challenges facing the potato processing industry and can result in significant yield reductions of around 10 to 20 per cent. The potato industry has a farm gate value of $137 million in Tasmania (2019-20) and better management options for powdery scab could help improve the economic competitiveness of the industry – contributing to the goal of growing the value of agriculture in Tasmania to $10 billion per year by 2050.

It is a focal point for a research team at the Tasmanian Institute of Agriculture (TIA), led by Plant Pathologist Professor Calum Wilson. Professor Wilson and his team have been working on multiple projects over several years to develop a better understanding of the disease and develop sustainable management practices.

“We know that the pathogen can lay dormant in the soil for ten or more years, and these resting spores cannot be destroyed using fungicides. This enduring nature of the pathogen makes is particularly difficult for growers to manage powdery scab disease, because even if they turn a paddock out to pasture for a decade the problem can persist,” Professor Wilson said.

“Our research has discovered that the resting spores are stimulated to germinate when they receive a chemical signal that is produced by the roots of a potato plant, releasing zoospores which are attracted to the roots and cause the infection.

“The good news is that zoospores survive for only a few hours. So, if we can stimulate germination in the absence of a host plant the pathogen will perish.”

Professor Wilson’s team have identified the precise chemical signals that cause the pathogen to germinate, and they know how to interfere with that process to eradicate the pathogen in the complete absence of a potato crop in the ground.

“Through this novel approach to disease management we are aiming to deplete soil inoculum before planting, improve fungicide efficiency, and disrupt infection during early potato growth,” Professor Wilson said.

Research moving to proof-of-concept

Over the past three years, this research has been accelerated through a project funded by Simplot Australia which is taking work to the proof-of-concept stage. Through this research program, two novel disease management concepts have been developed; Germinate to Exterminate and Diffuse to Confuse.

“We are looking at a new way of approaching disease management rather than using fungicides to try to eliminate the pathogen. We’re taking a more biological approach to interfere with the normal communication that happens under the ground between the pathogen and the soil environment,” Professor Wilson said.

“Trials conducted in the lab and plots have shown that the pathogen can be tricked into germinating in the absence of potatoes by replicating the compound that is produced by the plant’s roots. After germinating, the pathogen will only survive in the soil for a few hours before perishing.

“Our aim is to crash the population of pathogens below a threshold where the amount in the soil is unlikely to have a huge impact on a potato crop.”

The TIA researchers have developed a powder form that replicates the compound responsible for waking-up the powdery scab pathogen, and this has successfully been used in trials conducted in the lab and plots. Different application methods are being examined, including granules and a liquid form that could be incorporated within an existing fungicide application method.

“This approach will require multiple applications to target resting spores over several months. At this stage we think that an initial application would be required at least six months prior to planting. The treatment could be re-applied when planting a cover crop or even immediately after harvest,” Professor Wilson said.

“To develop this treatment, we are using natural products that already contain the key chemicals. There is an opportunity to repurpose waste materials to create the treatment and this is something that we are exploring,” Professor Wilson said.

Diffuse to Confuse

The second part of the research program is known as ‘Diffuse to Confuse’.

“Once germinated, the pathogen uses the same chemical signals to recognise where the roots are in the soil. Here we apply the treatment to the soil at the time of planting to try and confuse the infecting spores to follow a chemical trail that leads it away from the potato roots and thus avoid infection. This approach has shown promise in lab and plot trials,” Professor Wilson said.

Dr Audrey Leo, Research Scientist at Simplot Australia said the research program aims to reduce powdery scab disease which is ubiquitous to Tasmanian potato growing regions.

“This project has helped us to understand our ability to manipulate soil chemical composition occurring at the intersection of the host and the pathogen. The collaboration has enabled us to identify promising compounds that are efficacious in reducing powdery scab zoospores by at least 20 per cent in-vitro,” Dr Audrey Leo, Simplot Australia.

“These learnings are currently being applied and validated in-field with the aim to provide Simplot growers with a more effective powdery scab management strategy in the near future.”

Professor Wilson said the research has received strong interest from growers in Tasmania and New Zealand and growers will be involved in field trials over the next two to three years as treatments are refined.

“We are now focussing on identifying the effective rates, frequencies and timing of applications. The goal is to provide growers with practical advice about how this approach can integrate within existing production practices,” he said

“Of course, other methods for preventing and managing powdery scab include following best practice of maintaining soil health, volunteer control, irrigation management, soil testing, using certified seed and resistant varieties.”

This article was published in the September edition of the TFGA Farming Tasmania magazine.