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Common lambsquarters (Chenopodium album L.) is a broadleaf weed that can severely damage soybean fields. Two C. album populations (1744 and 1731) suspected resistant to imazethapyr were investigated for resistance levels to imazethapyr, thifensulfuron-methyl, and fomesafen and their resistance mechanisms were investigated. Whole-plant dose-response assays revealed that, compared to the susceptible (S) population, the 1744 population was 16.5-fold resistant to imazethapyr, slightly resistant to thifensulfuron-methyl (resistance index [R/S], <3). The 1731 population was 18.8-fold resistant to imazethapyr, 2.9-fold resistant to thifensulfuron-methyl, and 5.1-fold resistant to fomesafen. In vitro acetolactate synthase (ALS) assays showed 17.1-fold and 19.3-fold resistance levels of 1744 and 1731 populations to imazethapyr respectively. ALS gene sequence analysis identified Ala122Thr amino acid substitution in the 1744 population and Ser653Thr amino acid substitution in the 1731 population. No mutations of the protoporphyrinogen oxidase (PPO) gene were detected. However, pre-treatment with malathion reversed fomesafen resistance, suggesting nontarget-site resistance mechanisms likely play a role in the 1731 population. [Display omitted] • Chenopodium album L. showed multiple resistance to ALS- and PPO-inhibiting herbicides • ALS sequence analysis revealed Ala-122-Thr and Ser-653-Thr mutations in the resistant populations. • Chenopodium album L. showed enhanced metabolic resistance to fomesafen. [ABSTRACT FROM AUTHOR]

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 P450s-involved metabolism in S. viridis. [Display omitted] • Six Setaria viridis populations were highly resistant to nicosulfuron. • ALS sequencing revealed Asp-376-Glu and Pro-197-Ala mutations. • P450s inhibitor malathion could reduce nicosulfuron resistance in Setaria viridis. [ABSTRACT FROM AUTHOR]