TIA researcher Associate Professor Calum Wilson spoke about exciting new powdery scab research that has the potential to revolutionise the way growers manage this disease.

Powdery scab costs Australian potato growers around $13.4 million per annum.

Effective management of the disease is particularly important in Tasmania, as the state has the perfect storm of conditions for powdery scab.

“We have lots of inoculum in the soil, grow a lot of the Russet Burbank potato cultivar which shows fewer symptoms of tuber infection, and our soils are the world’s best at harbouring powdery scab disease,” Dr Wilson said.

Powdery scab is often thought of as a cosmetic disease of potato tubers.

However, a closer look reveals smaller and fewer roots can contribute to significant yield loss with only minor tuber symptoms.

Powdery scab can survive in soil for decades as tough resting spore ball structures known as sporosori. These are a conglomeration of up to a thousand resting spores, known as zoospores.

By understanding how and when these develop and interact with the potato, researchers can pinpoint the Achilles heel of this disease.

“The sporosori is a particularly clever structure in that it stays dormant until it receives a chemical signal from a potato root. We found that these chemicals trigger the sporosori spore ball to wake up and release its zoospores,” Dr Wilson said.

“These swim through the soil moisture, following the chemicals to their origin at the potato root, like a scent trail sniffed out by the zoospores. Once they reach the potato root they bind to it and a rapid cycling infection process begins.

“Unlike sporosori, individual zoospores are incredibly vulnerable and only live for around five hours. So our research is targeting the time when sporosori wake up and release the zoospores.”

The TIA research team aims to develop a multipronged solution to powdery scab. The first is a novel technique affectionately known as ‘germinate to exterminate’ where the sporosori is tricked into germinating and releases its vulnerable zoospores at a time when the crop isn’t present.

This is done by flooding the soil with chemical stimulants and but no potato host to attach to, so the zoospores die in a matter of hours.

This method has the potential to not only reduce powdery scab levels in the soil, but also shorten rotation times between crops.

The second technique takes its inspiration from insect lures used for codling moth.

In the case of powdery scab, the lure is the attractant chemicals produced by potatoes mixed with a fungicide.

The ‘attract and kill’ technique involves applying this lure to the infected soil. The zoospores are tricked into swimming towards the lethal fungicide lure.

Another proposal is to enhance both root production and the soil rhizosphere (the root-microbe-soil interface).

Encouraging the growth of bigger tougher roots that are more resistant to attack, whilst encouraging a microbial population that breaks down or eats the trigger chemical, could add an extra level of defence to the potato.