CHARACTERIZATION OF A SPONTANEOUS RAPESEED MUTANT TOLERANT TO SULFONYLUREA AND IMIDAZOLINONE HERBICIDES

A spontaneous chlorsulfuron tolerant variant, RCS-5, was isolated from protoplast culture of rapeseed, Brassica napus L. The tolerance level of the mutant was due to mutation of a single dominant gene resulting in an alteration of the acetolactate synthase enzyme. Seedling growth bioassays applied in vitro or after seed-soaking treatment showed tha t the mutant was 250-500 more tolerant to chlorsulfuron than the sensi tive control. Field tolerance was evaluated with commercial formulatio ns of chlorsulfuron (Glean T), triasulfuron (Keos), and metsulfuron me thyl (Allie), and an imidazolinone imazamethabenz (Meganet). The resul ts indicated that the mutant could tolerate a lower dose rate of sulfo nylureas than the dose recommended for cereal culture. In contrast, th e mutation provided a good protection against imazamethabenz. The poss ibility of using the protoplast-derived mutation in crop rotation and F1 hybrid seed purity assessment is also discussed. However, isolated lines of the mutant were found to be less productive and one week late r than the sensitive parent.