Molecular mechanism of resistance to mesosulfuron-methyl in shortawn foxtail (Alopecurus aequalis) from China

Abstract

Shortawn foxtail (Alopecurus aequalis Sobol.) is an obligate wetland plant that is widely distributed throughout Europe, temperate Asia, and North America. In China, it is widespread in the middle and lower reaches of the Yangtze River as a noxious weed in winter cropping fields with a rice (Oryza sativa L.) rotation. The acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron-methyl has been widely used to control annual grass and broadleaf weeds, including A. aequalis, in wheat fields, leading to the selection of herbicide-resistant weeds. In this study, an A. aequalis population AHFT-4 survived mesosulfuron-methyl at its field-recommended rate (9 g ai ha-1) was collected in Anhui Province. Single-dose testing confirmed that suspected AHFT-4 had evolved resistance to mesosulfuron-methyl. Target gene sequencing revealed a resistance mutation of Pro-197-Ala in ALS1 of the resistant plants, and a derived cleaved amplified polymorphic sequence (dCAPS) marker was developed to specifically detect the mutation. Relative expression assay showed no significant difference in ALS expression between AHFT-4 and a susceptible population without or with mesosulfuron-methyl treatment. Whole-plant dose-response bioassays indicated that AHFT-4 had evolved broad-spectrum cross-resistance to ALS-inhibiting herbicides of all five chemical families tested, with GR50 resistance index (RI) values ranging from 21 to 206. However, it remained susceptible to the photosystem II inhibitor isoproturon. Pre-treatment with the cytochrome P450 inhibitor malathion or the glutathione S-transferase inhibitor 4-chloro-7-nitrobenzoxadiazole (NDB-Cl) had no significant effects on the resistance of AHFT-4 to mesosulfuron-methyl. To our knowledge, this study reports for the first time the ALS gene Pro-197-Ala substitution conferring broad-spectrum cross-resistance to ALS-inhibiting herbicides in A. aequalis.

Metabolism-Based Nontarget-Site Mechanism Is the Main Cause of a Four-Way Resistance in Shortawn Foxtail (Alopecurus aequalis Sobol.)

“…Whole-plant dose–response bioassays were conducted to assess the susceptibility of the S (AHFY-3) and putative R (AHFT-3) populations to various herbicides with distinct MOAs (Figure ). These bioassays were conducted concurrently with the relevant experiments carried out in our previous studies, , ensuring consistency in the susceptibility levels of AHFY-3 to different herbicides as observed previously. In this study, all 12 tested herbicides exhibited effective control against the S plants, with GR 50 values well below their respective RFRs (Table , Table S1).…”

“…aequalis treated with a range of doses of (A,B) fenoxaprop- P -ethyl, (C,D) mesosulfuron-methyl, (E,F) isoproturon, and (G,H) bixlozone plus or minus specific doses of P450 or GST inhibitor. Some curves presented in the figure were reused with permissions from both ref , Copyright 2024 Cambridge University Press, and ref , Copyright 2024 John Wiley and Sons. For fenoxaprop- P -ethyl and isoproturon, piperonyl butoxide (PBO) was used as the P450 inhibitor and applied at 4200 g ai ha –1 .…”

“… a Some data presented in the table were re-used with permissions from both ref , Copyright 2024 Cambridge University Press, and ref , Copyright 2024 John Wiley and Sons. Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase; PSII, Photosystem II; DXS, 1-deoxy- d -xylulose-5-phosphate synthase; APP, aryloxyphenoxypropionate; CHD, cyclohexanedione; PPZ, phenylpyrazoline; SU, sulfonylurea; IMI, imidazolinone; TP, triazolopyrimidine; PTB, pyrimidinyl-thiobenzoate; SCT, sulfonyl-aminocarbonyl-triazolinone; ILD, isoxazolidinone; PBO, piperonyl butoxide; and NBD-Cl, 4-chloro-7-nitrobenzofurazan. b * P < 0.05; ns, not significant. …”

“…aequalis to different herbicides, including (A) clodinafop-propargyl, (B) sethoxydim, (C) clethodim, (D) pinoxaden, (E) imazethapyr, (F) pyroxsulam, (G) pyrithiobac sodium, and (H) flucarbazone-sodium. Some curves presented in the figure were reused with permission from ref , Copyright 2024 Cambridge University Press. Vertical bars represent SEs of the means.…”

“…Another A. aequalis population, AHFY-3, kept in the laboratory, had been confirmed as susceptible to different herbicides and served as a susceptible (S) control in this study. , …”