Resistance to acetolactate synthase-inhibiting herbicides in shattercane and johnsongrass: Current status and future predictions.

摘要

Traditional breeding is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. This technology (Inzen, DuPont) has the potential to improve sorghum production by allowing for the postemergence control of traditionally hard-to-control grasses. However, grain sorghum and shattercane can interbreed, and introduced traits such as herbicide tolerance could increase the invasiveness of the weedy relative. Moreover, ALS-resistance in shattercane populations has been reported, indicating that over-reliance on ALS-chemistry may also select for resistant biotypes. In 2013, seeds from 190 shattercane and 59 johnsongrass populations were collected with the objective to evaluate the distribution of ALS-resistance in weedy-sorghum populations across northern Kansas and Nebraska. Five shattercane and five johnsongrass populations were confirmed resistant to imazethapyr. Four shattercane and three johnsongrass populations were confirmed resistant to nicosulfuron. All ALS-resistant shattercane and johnsongrass populations were collected in Nebraska except for one nicosulfuron-resistant johnsongrass population collected in Kansas. Inzen sorghum will carry a double mutation in the ALS gene (Val560Ile and Trp574Leu), which confers high levels of resistance to ALS herbicides. Primers specific to the Val560 and Trp574 region of the ALS-gene were used to screen populations using PCR. The Trp574Leu mutation was present in one ALS-resistant johnsongrass population. The Val560Ile was detected in resistant and susceptible shattercane and johnsongrass populations, indicating that by itself, Val560Ile amino acid substitution does not confer resistance to ALS-inhibiting herbicides. None of our populations presented both mutations simultaneously, as does Inzen sorghum. This research indicates that ALS-resistance persists and that ALS mutations present in Inzen sorghum already exist individually in weedy-sorghum populations. According to our modeling efforts, evolution of resistance was predicted to occur rapidly if Inzen sorghum is planted continuously because of high selection pressure (ALS-herbicide application) and gene flow. The time for resistance evolution was predicted to decrease with increased cropping system complexity (more crop diversity than continuous production of Inzen). Rotating Inzen sorghum with non-sorghum crops where effective herbicide options are available will be a key strategy to keep shattercane populations at low levels while postponing the evolution of ALS-resistance to some extent.