Informing management of potato diseases through epidemiology and diagnostics

There had been several projects in GB prior to 2010, mostly funded by AHDB Potatoes, examining the use of DNA-based tests to study potato blemish diseases. The results from a couple of the projects contributed to the development of a black dot risk assessment guide. Attempts to develop a risk assessment for black scurf and stem canker, incorporating the results DNA-based tests for Rhizoctonia solani, had proved to be more difficult

Collaboration

During 2010- 2012 AHDB Potatoes-funded researchers participated in an international collaboration to improve the reliability and interpretation of results from DNA-based diagnostic tests. The programme of work involved researchers in GB, Australia, South Africa and New Zealand. The collaboration allowed a greater range of experiments to be completed whilst ensuring that there was no duplication of effort on diagnostics development. The main focus of the work was soil and seed borne diseases including powdery scab, Rhizoctonia and common scab, although black dot and root knot nematode (Meloidogyne fallax) diagnostics have also been studied.

The Australian component of the diagnostics work continued until winter 2014. Risk assessments based on DNA-based soil test results have been validated on commercial crops in South Australia, Victoria and Tasmania.  The tests are being offered as a commercial service (PreDicta Pt) in Australia and provide an indication of the risk of powdery scab, black dot and root knot nematode (M. fallax). DNA levels of Streptomyces txtA gene (associated with the development of common scab), R. solani AG3, R. solani AG2.1, Meloidogyne hapla and Verticillium dahliae are reported. However, these results are provided for information only as sensitivity and risk categories are not available for these tests. DNA-based tests for some of the pathogens (eg black dot, powdery scab) are also offered by research providers such as Fera and SRUC in GB. These were developed using results from a range of trials carried out in GB.

It has not proven possible to develop risk assessments for R. solani based on soil test results, primarily because the research work in GB identified cases where soil samples tested negative for R. solani but disease caused by the pathogen subsequently developed in the crop. These anomalies are attributed to the distribution of R. solani in soil, which may mean that soil sampling protocols suitable for other soil borne pathogens do not apply to R. solani.

The final report of the British component of the project and a review of information on R. solani are available below.

The Australian project (PT09023) is part of the broader Australian Potato Research Program Phase 2 (APRP2), conducted for the Australian processing potato industry. The program is funded by Horticulture Australia Limited (HAL) using the National Processed Potato Levy, voluntary contributions from industry, and matched funds from the Australian Government.