Target site mutations and cytochrome P450s confer resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl in Alopecurus aequalis: TSR- and NTSR-based resistance in Alopecurus aequalis

BACKGROUND: Shortawn foxtail (Alopecurus aequalis Sobol.) is a competitive grass weed infesting winter wheat- and canola-growing fields in China. In May 2016, a suspected A. aequalis resistant population AHTC-06 that survived fenoxaprop-P-ethyl and mesosulfuron-methyl applied at their field-recommended rates was collected from a wheat field in Jinji County, Anhui Province, China. This study aimed to determine the resistance profile of this AHTC-06 population to ACCase- and ALS-inhibitors, and to investigate its mechanisms of resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl. RESULTS: Two mutations, a common Ile-2041-Asn (ACCase gene) and a very rare Pro-197-Tyr (ALS1 gene), were both identified in resistant individual plants. The homozygous subpopulation AHTC-06F1 for the two mutations was generated, and it showed broad-spectrum resistance to APPs, DENs, and ALS-inhibiting herbicides of all five chemical families tested, with resistance index (RI) values that ranged from 2.2 to 36.5. In vitro ALS activity assays showed the ALS from the resistant population was insensitive to all the tested ALS inhibitors, with RI values ranging from 3.10 to 22.51. Pre-treatment with piperonyl butoxide (PBO) and malathion significantly (P < 0.05) reversed the weed's resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl, respectively. Two P450 genes, c21190_g1 and c43350_g3, were constitutively overexpressed and mesosulfuron-methyl-induced upregulated in resistant plants, for which c43350_g3 was also fenoxaprop-P-ethyl-induced upregulated. CONCLUSION: This study confirms the first case of a grass weed featuring broad-spectrum resistance to ALS-inhibiting herbicides due to a Pro-197-Tyr mutation in the ALS gene. Fenoxaprop-P-ethyl and mesosulfuron-methyl resistances in AHTC-06 plants were conferred by target site mutations and P450s-based metabolism. © 2018 Society of Chemical Industry.