New DNA test targets £10m threat to UK onion industry

Onion growers could soon have a new weapon against a devastating disease that costs the UK industry an estimated £10 million a year.

A new soil test developed by the University of Warwick’s Crop Centre and ADAS will allow growers to detect the pathogen responsible for Fusarium Basal Rot before onions are planted.

The disease is one of the biggest threats facing the onion sector, with some growers losing up to 40% of crops and, in severe cases, entire onion stores after harvest.

With no treatment currently available once crops become infected, prevention and field selection remain the only effective ways to manage the disease.

Fusarium Basal Rot is caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. cepae (FOC), which infects onion crops through their roots.

One of the major challenges for growers is that infected crops often show few visible symptoms until bulbs begin rotting in storage, by which point significant losses may already have occurred.

Industry experts say the new DNA-based test is the first commercially available system capable of detecting the disease-causing fungus directly from soil samples before planting.

The test was developed as part of the two-year FUSED project, funded by Innovate UK and Defra.

Researchers at the University of Warwick say the technology could help growers avoid planting onions in high-risk fields and reduce potentially costly storage losses later in the season.

Professor John Clarkson, plant pathologist at the University of Warwick and lead on the project, said detecting Fusarium in soil had previously been extremely difficult, limiting growers’ ability to assess risk effectively.

“Through a process of enrichment and DNA extraction, we are now able to confirm how prevalent the FOC pathogen is in a given soil sample,” he said.

The soil test is now commercially available through ADAS, which helped develop the technology for use across the industry.

Results are typically returned within 15 days, with growers advised to carry out testing before planting begins.

ADAS Biotechnology managing director Dr Ben Maddison said the results would be presented using a traffic light system to help growers understand disease risk levels.

“The results come with a traffic light system to indicate how serious the risk to crop may be and the damage it could do, allowing growers to plan their planting accordingly,” he explained.

Maddison said growers concerned about Fusarium Basal Rot should consider testing fields before cropping decisions are made.

“Unfortunately, Fusarium Basal Rot remains untreatable for now, but it is no longer unavoidable,” he said.

British Onion Producers’ Association chair Ben Collins said levels of Fusarium had risen sharply across the UK onion sector over the past 15 years.

He said the new testing system would help growers make more informed decisions before planting and reduce the financial impact caused by the disease.

The industry hopes the new tool will help cut heavy crop losses and give growers a practical way to tackle one of the sector’s most costly and difficult diseases.