Molecular basis of resistance to mesosulfuron-methyl in Japanese foxtail, Alopecurus japonicus

Japanese foxtail (Alopecurus japonicus) has developed resistance to the acetolactate synthase (ALS) herbicide mesosulfuron-methyl, which has been used continuously for several years in winter wheat fields in eastern China. To ascertain the resistance degree of A. japonicus to mesosulfuron-methyl, whole-plant bioassays and in vitro inhibition assays were conducted. The results of the whole-plant bioassays showed that the resistance index of the resistant population, JS-5, to mesosulfuron-methyl was 100-fold higher than that of the susceptible population, JS-7, and the in vitro activity assays confirmed that the ALS sensitivity of the JS-5 to mesosulfuron-methyl was reduced. To further investigate the molecular basis of the resistance, the ALS genes of the JS-5 and JS-7 populations were cloned, sequenced, and compared. Gene sequence analysis revealed a proline-to-threonine substitution at amino acid position 197 of ALS in Domain A that potentially confers the resistance of A. japonicus to mesosulfuron-methyl in the JS-5 population.