Target site mutations and cytochrome P450s-involved metabolism confer resistance to nicosulfuron in green foxtail (Setaria viridis)

Green foxtail [Setaria viridis (L.) P.Beauv.] is a troublesome grass weed that is widely distributed in maize (Zea mays L.) fields across China. Many populations of S. viridis have evolved resistance to the acetolactate synthase (ALS)-inhibiting herbicide nicosulfuron. The objectives of this research were to confirm nicosulfuron resistance in these populations and to investigate the basis of nicosulfuron resistance. Whole-plant dose-response experiments showed 6 out of 13 S. viridis populations were highly resistance (20-30 times) to nicosulfuron. Sequencing of the ALS gene revealed two amino acid mutations, Asp-376-Glu and Pro-197-Ala, in the nicosulfuron-resistant populations. A malathion pretreatment study revealed that the R376 and R197 subpopulations might have cytochrome P450s-mediated herbicide metabolic resistance. The resistant populations were cross-resistant to imazethapyr but sensitive to topramezone and quizalofop-p-ethyl. This is the first report of resistance to ALS inhibitors conferred by target site mutations (Asp-376-Glu or Pro-197-Ser) and possible cytochrome P450sinvolved metabolism in S. viridis.

Automated summary

Green foxtail is a troublesome weed in maize fields in China, with many populations showing high resistance to the herbicide nicosulfuron. Resistance was found to be associated with two amino acid mutations in the ALS gene and potentially mediated by cytochrome P450s. The resistant populations were also cross-resistant to imazethapyr but sensitive to other herbicides.