Integration of precision irrigation and non-water based measures to suppress common scab of potato

The role of seed-borne Streptomyces in common scab development was confirmed to be minor in comparison with that of soil-borne inoculum. Prediction of the likelihood of disease development from streptomycete populations in soil pre-planting is likely to be unreliable as pathogenic Streptomyces populations were often undetectable in the soil before planting, even in plots where disease subsequently developed.

The changes in populations of other non-pathogenic bacteria (actinomycetes) were monitored alongside the pathogenic species. This was done to test the hypothesis that the ratio of pathogenic : non-pathogenic bacteria is important in scab control. In the field trials, the build -up of pathogenic Streptomyces species on initiating tubers and the resulting common scab levels varied from field to field and appeared to be inversely related to the total actinomycete activity of the soil during tuber initiation.

Non-water based control measures (soil amendments with sulphur or rapeseed meal) did not have consistent beneficial effects in reducing common scab on tubers.

Work to study the effects of irrigation timing and frequency on scab incidence and severity; and methods to study the whole microbial community on tuber peel were developed further in projects R429 and R448.

The project was sponsored by Defra through the Sustainable Arable LINK programme with funding from the AHDB Potatoes, Cobrey Farms, Branston Ltd, QV Foods Ltd and Wroot Water Systems.