Root mat disease now affects almost nine out of 10 tomato nurseries in the UK and AHDB Horticulture is taking important steps to help growers tackle this widespread problem.

Root mat disease leads to a hormone imbalance that can cause root proliferation in tomato plants. Affected plants often produce fruit outside of retailer specifications and root systems can become more susceptible to infection by other pathogens. In rare cases, root systems can become so dense the plant can no longer take up water effectively.

In response to industry concerns about the disease, AHDB Horticulture set up a project to identify better ways to diagnose the presence of root mat before severe symptoms are seen and find reliable control methods.

Dr Phil Morley, ‎director of agronomy at APS Salads Ltd and technical officer at British Tomato Growers Association said: “Root mat has the potential to cause significant crop loss, both through a reduction in overall yield and a reduction in quality resulting in unsaleable fruit. In the current climate, when margins are being reduced and costs increased once more, growers must maximise their saleable yields and get the most out of their crops to remain profitable. Reduction of root mat where already present and, indeed, prevention of spread to non-affected nurseries is thus a priority.“

During the past year, research at Fera Science Ltd has been developing a molecular diagnostic technique.

Root mat is established when the bacterium Rhizobium radiobacter releases plasmids, which are self-contained pieces of DNA. Genes on the plasmids then become incorporated alongside those of the host tomato roots, facilitating further infections and inducing the root mat symptoms.

Researchers established that the incorporated plasmid genes of the UK root mat pathogens could be detected by the same kind of test that has become widely used to pick up and measure other plant pathogens. However, Fera first had to devise a new DNA extraction method to obtain the relevant DNA sequences directly from root tissue.

John Elphinstone, senior phytobacteriologist at Fera, said: “The method we have been developing has shown to be as effective and accurate as previous, more laborious techniques. We believe this method will enable young propagation material to be screened for infection before transplanting.”

At the same time, ADAS has been screening crop protection and biocide products to identify potential treatments. The work so far has identified some products to take forward to larger scale trials, which will run throughout 2017 on commercial tomato nurseries.

Gracie Emeny, knowledge exchange manager at AHDB Horticulture, said: “We hope the diagnostic technique that has been developed will help growers make significant financial savings through a reduction in infected plants through early diagnosis and reduced crop losses. Further work within the scope of this project is also looking at the best biological controls to use to control the disease once diagnosed, as well as looking at treatments applied in propagation of young plants so that they remain free from infection before being transported to growers. This will further help growers by avoiding the costly expense of using ineffective control methods.”

Dr Morley added: “Root mat has affected several British tomato producers over the years to a greater or lesser extent. Estimates of actual financial costs vary, dependent on the extent and severity of the issue in crops. However, it is clear that this disease has the potential to significantly increase costs where remedial crop management strategies are required and directly reduce yield and thus income.”