What was it all about?

This project, which ran from 2018 to 2023, developed a rapid, cost-effective screening process to determine the level of resistance different potato cultivars have to powdery scab infection. The research improved industry understanding of how the powdery scab pathogen binds to potato roots and identified possible targets for breeding of resistant potatoes.

Spongospora subterranea is responsible for powdery scab of tubers and for root disease that disrupts root function leading to reduced growth and yields. Managing these diseases is extremely difficult, and largely relies on resistant cultivars. Traditionally, the identification of disease resistance has been based on the visual assessment of disease in large field or glasshouse trials, which are both time and resource intensive.

This research developed a rapid cost-effective screen for cultivar resistance to root infection. It focused on the very first phase of interaction between the pathogen and plant where pathogen spores bind to potato roots initiating infection. Using this assay, 153 potato lines were screened for their relative resistance to root infection showing a continuum of resistance expression.

Then, using a cell selection technique, the research team generated variants of fresh market and processing cultivars which were screened using the new assay. Lines of each cultivar appeared to have enhanced resistance to root infection. These were then tested in repeated glasshouse trials which were able to confirm enhanced disease resistance. These lines require further agronomic testing to determine commercial potential but show great promise for reducing root disease and demonstrate the potential of cell selection techniques for generating disease resistance across a range of potato cultivars.

The project then focused on obtaining a better understanding of the nature of pathogen root attachment. Firstly, the whole roots of resistant and susceptible varieties were examined for expression of proteins which may indicate genes responsible for resistance (or susceptibility). More abundant proteins in the resistant lines included those associated with the phenylpropanoid biosynthesis pathway, suggesting a role of lignin biosynthesis in host resistance, glutathione metabolism and enzymes involved in pectin biosynthesis and remodelling.

Sophisticated proteomic and enzyme digestion techniques were then used to focus on proteins found on the root surface. Evidence was found for the importance of glycoproteins on the root surface that enable pathogen binding. For example, a 28 kDa glycoprotein was less abundant in resistant varieties which suggests it could be a pathogen recognition factor. Glutathione metabolism and lignin biosynthesis pathway were again found to be more abundant in resistant cultivars. These findings provide possible targets that could be useful in breeding for resistance (or removal of susceptibility).

Lastly, a genetic screen was undertaken of a large range of potato cultivars to look for markers specific to the root attachment trait. Covid-restrictions during the project meant the project team were unable to source as many varieties as planned, and the power of the analysis was subsequently limited, however linking the gene marker data with the proteomic data should clarify useful markers.