Field and laboratory assessments of sugarcane mutants selected in vitro for resistance to imazapyr herbicide

Seven imazapyr-tolerant mutant sugarcane plants, previously generated by in vitro mutagenesis, were studied. The imazapyr concentrations required to inhibit their acetolactate synthase (ALS basal activity) (IC50 as μmoles acetoin h-1 mg-1 protein) were 0.77 - 5.36 times greater than that of the N12 ‘parent’. The basal ALS activities of Mut1 and Mut6 were 1.4-fold higher than that of N12. When the mutants were sprayed with Arsenal® GEN 2 (312 and 624 g a.i. imazapyr ha-1), 2 months after field planting, and evaluated 9 months later, live stalk height and number were significantly lowest in Mut2, Mut3 and the control N12. No differences in sucrose, fibre and estimated yield were observed amongst lines in untreated plots. Mutant plants germinated and grew in soil treated with the herbicide (at the lethal dose of 1248 g a.i. ha-1). The Mut lines tested in this study offer improved options for weed control.