Development and evaluation of a technique for screening watercress (Rorippa nasturtium‐aquaticum) for resistance to watercress yellow spot virus and crook‐root fungus (Spongospora subterranea f. sp. nasturtii)

Abstract

A technique was developed for screening large numbers of watercress plants for resistance to watercress yellow spot virus (WYSV) and the crook‐root fungus. Plants were raised in modules containing sand in the glasshouse, transported and placed in experimental watercress beds, recovered after 5 or 6 weeks, examined visually for crook‐root infection and tested by ELISA for infection by WYSV. High incidences of crook root (98.8%) and virus (88.9%) were obtained in a watercress line known to be susceptible to both pathogens. Evaluation of the technique using 10 different watercress lines showed that it was capable of revealing a range of responses from very susceptible to very resistant, with UK lines being most susceptible to both diseases. When grown on, the very resistant line was different morphologically from UK watercress and was identified as early winter‐cress (Barbarea verna). Results showed an association between crook root scores and ELISA values, providing further circumstantial evidence for the close relationship between the two pathogens. The implications of the results for watercress resistance screening are discussed.