International project on potato diseases

New international work is under way to help potato growers assess the risk, before planting, of their crops getting powdery scab and rhizoctonia.

The Potato Council-funded £430,000 three-year study involves SCRI, SAC and the Food and Environment Research Agency (formerly CSL) with partners in Australia, New Zealand and South Africa.

It follows the success of earlier UK work which led to the DNA-based black dot prediction scheme now available as a commercial testing service.

Black dot is well suited to such diagnostic techniques, says the Potato Council’s Sue Cowgill. “The test will give you valuable information about how the disease will develop – whether you are looking for just an indication of how much of the pathogen is present or management advice based on the results.”

That advice was summarised in the council’s guide Managing the risk of black dot sent to levy-payers.

But getting to grips with other diseases, such as powdery scab and rhizoctonia, to allow similar reliable tests to be developed is a tougher challenge, which Dr Cowgill hopes the international collaboration will help overcome.

Predicting powdery scab is particularly tricky, she says.

“Both seed and soil-borne inoculum can cause the disease, but this isn’t the problem when it comes to determining its extent on progeny crops. Environmental conditions, such as wet summers, have much more influence.”

Forecasting rhizoctonia, which causes black scurf, is also far from straightforward in that it has developed on plants grown from disease-free mini-tubers even in soil where no inoculum has been detected.

“We think this comes down to how it’s distributed in the field. Its spread is probably patchier than black dot, which makes getting a representative sample more difficult.”

The international consortium aims to improve detection of such soil-borne pathogens through standardised testing, says colleague Mike Storey.

“We initially identified research synergies through discussions with our counterparts at Horticulture Australia.”

The non-competitive project has several benefits. “It’s a great opportunity to extend limited resources, gives a larger pool of research data, and we can share knowledge with leading international experts.

“By conducting trials in both the southern and northern hemisphere we can maximise seasons and study two crops a year, gaining data much faster.”

The research will evaluate the causes, distribution and control of soil-disease populations using the latest laboratory real-time PCR assays to test for pathogen presence, says Dr Storey.

“At the end of the study we hope to develop pre-planting tests that give you a quick, accurate assessment of disease risk of powdery scab and rhizoctonia in field conditions.”

The findings will be made available to levy-payers for disease risk assessment and decision-making purposes, along with disease control advice at the end of the study.

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