Verticillium longisporum: pathogen detection, diagnostics and cultivar resistance in U.K. oilseed rape (Brassica napus)
Abstract: Verticillium longisporum is an emerging pathogen of oilseed rape (Brassica napus) in the U.K. and both incidence/distribution of the disease appears to be increasing. The delay in the expression of symptoms in the host and the soil-borne nature of the pathogen hamper accurate detection and diagnosis. Chemical control strategies are currently ineffective and rotational management is the only option to minimise risk of disease. The identification of sources of genetic resistance is therefore a desirable strategy through which to reduce disease. In an effort to identify strategies to manage the risk posed by V. longisporum we generated a series of inoculated trials to screen a range of current U.K. varieties for resistance and used a CTAB/silicon dioxide pre-extraction, followed by conventional extraction to obtain DNA from a range of soil samples for subsequent analysis. Development of Loop Mediated Isothermal Amplification (LAMP) and qPCR based assays have enabled us to accurately detect and diagnose V. longisporum in a range of naturally and artificially infected soil samples. B. napus varieties varied for incidence of the disease and although complete resistance would appear to be absent in the varieties screened, a range of partial resistance was observed in specific cultivars. Detection assays currently provide semi-quantitative data for respective DNA concentrations and low (< 50 microsclerotia/50 g soil), moderate ( 200/50 g soil) levels of infection can be detected. The identification for variation in resistance to V. longisporum amongst current varieties and the development of new diagnostic techniques will be utilised to investigate pathogen dynamics, yield loss and also to develop strategies to manage the risk posed to growers.