Determining the ability of a novel quantitative PCR assay to detect latent infections of Polyscytalum pustulans and its use as an early indicator of skin spot risk

Although the skin spot pathogen (Polyscytalum pustulans) may be present on tubers at harvest, symptoms of the disease don't develop until many weeks later, by which time controlling the disease is difficult. An eye-plug test was available that could be used to identify infected stocks prior to planting, however the test took at least 5 days to complete and the assessments could be difficult because the plugs can become overgrown with common contaminants. Development of a molecular test would provide a more rapid method for the detection and quantification of the pathogen.

The aim of this project was to develop a test that would allow reliable, early detection of the skin spot pathogen - providing more opportunity to minimise disease development. 

Prior to the project, none of the genetic data needed to develop a molecular test existed for P. pustulans. During the course of the project the gene sequence data was generated and used to develop a molecular assay based on the real-time polymerase chain reaction (PCR). Cultures of related fungal species were tested to check the specificity of the assay and no cross-reactions were observed.

P. pustulans was detected in symptomatic and asymptomatic potato tubers, proving the test had the potential to detect the pathogen prior to skin symptoms being visible. A mobile testing system was set-up and a range of potato stocks tested. The real-time PCR assay was successful in discriminating between low and moderate levels of skin spot based on the quantity of pathogen-specific DNA detected in tuber peel.

To determine if DNA-based diagnostics can be developed for Polyscytalum pustulans and can be used to identify stocks with a high risk of developing skin spot.