Detection of viable downy mildew inoculum in seed stocks

Aerial oomycete pathogens can be seed-borne, or carried with seed, in many plant species. Molecular diagnostic tests have been developed that can detect the presence of DNA of target pathogens in some cases, but the viability of pathogen propagules remains elusive, and lengthy grow-on tests or time consuming microscopy are required to determine whether the pathogen has the ability to infect a growing plant. Moreover, the significance of any seed-borne disease in epidemic development is usually unknown. The study aims to implement novel molecular diagnostic tests for the detection of viable seed-borne downy mildew inoculum in several species, e.g. spinach (Spinacia oleracea), basil (Ocimum basilicum), and column stocks (Matthiola incana). The study will also elucidate the significance of any detected levels of viable inoculum in epidemic development in field and controlled environment experiments in order to derive indicative threshold levels, and improve disease management and whether or not seed-borne inoculum could have been responsible for recent aggressive outbreaks, e.g. in columns stocks. The value of sensitive molecular diagnostic tests is determined by the extent to which the tested portion is representative of the seed batch. Different sampling approaches will be tested to define minimum sub-sample numbers and sizes to assign acceptable confidence limits to test results. Results will be validated through commercially available test protocols and recommended sampling procedures.