Inhibition of acetolactate synthase in susceptible and resistant biotypes of Stellaria media

Abstract Acetolactate synthase (ALS) from one susceptible and two chlorsulfuronresistant biotypes of Stellaria media(L.) Vill. was assayed in the presence of eight known ALS inhibitors. As expected, ALS from the chlorsulfuronresistant biotypes (R1 and R2) showed reduced sensitivity to chlorsulfuron and other sulfonylurea herbicides. The patterns of cross‐resistance varied, however, indicating that the alteration in ALS that confers chlorsulfuron resistance does not confer the same level of resistance to other sulfonylurea herbicides. The resistant biotypes were highly cross‐resistant to sulfometuron‐methyl and DPX‐A7H81, but less cross‐resistant to triasulfuron. Both R1 and R2 were highly cross‐resistant to DTPS (N‐[2,6‐dichlorophenyl]‐5,7‐dimethyl‐1,2,4‐iriazolo[1,5a]pyrimidine‐2‐siilfoiiamide), but only slightly cross‐resistant to imazamethahenz, an imidazolinone herbicide. The differences in the patterns of cross‐resistance observed presumably reflect differences in the binding affinity of the herbicides for the altered ALS. The data presented suggest, but do not confirm, that R1 and R2 contain the same ALS mutation.