Genetic diversity within commercial populations of watercress (Rorippa nasturtium-aquaticum), and between allied Brassicaceae inferred from RAPD-PCR

Commercial productivity of watercress ( Rorippa nasturtium-aquaticum) can b e adversely affected by the pathogenic crook-root fungus, Spongospora subte rranea f.sp. nasturti, and watercress viruses. As there are no effective co ntrol measures for these diseases, attempts have been made to breed varieti es resistant to the crook-root pathogen. This work has been hindered by a l ack of knowledge of the genetic base of commercial watercress, and the gene tic distance between watercress and allied Brassicaceae which have been ide ntified as candidates for hybridisation programmes. We measured the diversi ty within these two groups using the RAPD-PCR fingerprinting technique and analysed the data by both distance methods and principal co-ordinate analys is. Little genetic diversity was found within commercial watercress populat ions. However, watercress formed a unique cluster genetically distinct from other Rorippa species, but equidistant to Cardamine species. It was placed closer to Barbarea verna.