Introduction
Digitaria spp. are annual grass weeds that are widely distributed in dryland ecosystems like roadsides, wastelands, and orchards, as well as in crops across the world (Laforest et al. Reference Laforest, Soufiane, Simard, Obeid, Page and Nurse2017; Liu et al. Reference Liu, Hou, Zhang, Merchant, Zhong, Ma, Zeng, Wu, Zhou, Luo and Ding2023; Yu et al. Reference Yu, McCullough and Czarnota2017; Zhao et al. Reference Zhao, Xu, Li, Qi, Huang, Hu, Wang and Liu2023). Digitaria ciliaris var. chrysoblephara (Fig. & De Not.) R.R. Stewart is an annual Gramineae weed that has gradually invaded dry-seeded rice fields in recent years (Guo et al. Reference Guo, Zhang, Zhang and Tian2022). Owing to its strong capacity to adapt to different environments and its high seed production, this weed competes with rice and has become a dominant grass weed in direct-seeded rice fields of China (Cao et al. Reference Cao, Tao, Zhang, Gu, Li, Lou and Wang2023; Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023).
Few postemergence herbicides have been registered for controlling Digitaria spp. weeds in rice fields, and farmers rely heavily on acetyl-CoA carboxylase (ACCase) inhibitors such as metamifop and cyhalofop-butyl. These herbicides cause plant death by binding selectively to the carboxyl transferase (CT) domain of plastidic ACCase and are allowed for grass weed control in rice fields as a selective compound (Kaundun Reference Kaundun2014). ACCase-inhibiting herbicides can be classified within the aryloxyphenoxypropionates (APPs), cyclohexanediones (CHDs), or phenylpyrazoline (DEN) chemical families according to different chemical structures (Powles and Yu Reference Powles and Yu2010). Given their high selectivity and safety to rice, ACCase-inhibiting herbicides were preferred by Chinese farmers for managing annual grass weeds postemergence in paddy fields. However, the extensive use of this mode of action (MOA) has resulted in the evolution of herbicide resistance in at least six Gramineae weed species in rice cultivation systems of China. For instance, populations of the noxious barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] (Sun et al. Reference Sun, Niu, Lan, Yu, Cui, Chen and Li2023), Echinochloa glabrescens Munro ex Hook. f. (Li et al. Reference Li, Zhao, Jiang, Wang, Zhang, Cao and Liao2023; Zhao et al. Reference Zhao, Xu, Li, Qi, Huang, Hu, Wang and Liu2023), rice barnyardgrass [Echinochloa phyllopogon (Stapf) Koso-Pol.] (Zhang et al. Reference Zhang, Wang, Du, Deng, Bai and Ji2023), D. ciliaris var. chrysoblephara (Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023), Malabar sprangletop [Diplachne fusca (L.) P. Beauv. ex Roem. & Schult.] (Yuan et al. Reference Yuan, Di, Chen, Chen, Cai and Deng2019), goosegrass [Eleusine indica (L.) Gaertn.] (Deng et al. Reference Deng, Li, Yao, Duan, Yang and Yuan2023a), and Chinese sprangletop [Leptochloa chinensis (L.) Nees ex.] (Deng et al. Reference Deng, Li, Yao, Wu, Zhu, Yang and Yuan2023b) have been confirmed resistant to ACCase-inhibiting herbicides.
Resistance to ACCase-inhibiting herbicides is caused by a non–target site based resistance (NTSR) mechanism and/or a target site–based resistance (TSR) mechanism (Délye et al. Reference Délye, Jasieniuk and Le Corre2013). NTSR to ACCase inhibitors is mainly involved in enhanced metabolism due to a change in the metabolic enzyme activity, such as cytochrome P450 monooxygenase and glutathione transferase. (Deng et al. Reference Deng, Yang, Li, Xia, Chen, Yuan and Yang2021; Yang et al. Reference Yang, Yang, Zhu, Wei, Lv and Li2022). TSR to ACCase inhibitors involves alterations of the target-site protein structure owing to specific amino acid changes in the CT domain or/and increased abundance of the target protein resulting from ACCase gene duplication or overexpression (Laforest et al. Reference Laforest, Soufiane, Simard, Obeid, Page and Nurse2017). Thus far, a total of 17 resistance-endowing mutations at ACCase codon positions Ile-1781 (substituted by Leu/Thr/Val), Leu-1818 (Phe), Trp-1999 (Cys/Leu/Ser), Trp-2027 (Cys/Leu/Ser), Ile-2041 (Asn/Val), Asn-2078 (Glu/Gly), Cys-2088 (Arg), and Gly-2096 (Ala/Ser) have been reported in grass weeds, and they usually confer cross-resistance to some of the ACCase inhibitors (Gaines et al. Reference Gaines, Duke, Morran, Rigon, Tranel, Küpper and Dayan2020; Jin et al. Reference Jin, Chen, Deng and Tang2022; Zhang et al. Reference Zhang, Chen, Song, Cang, Xu and Wu2022).
Metamifop is an APP herbicide that was introduced to China in 2010 and showed high herbicidal activity against grass weeds in rice-cropping systems, including Digitaria spp., Echinochloa spp., and L. chinensis (Cao et al. Reference Cao, Tao, Zhang, Gu, Li, Lou and Wang2023). In recent years, it has been increasingly observed that metamifop has had poor effect in controlling Digitaria spp. weeds in direct-seeded rice fields of China, especially in Jiangsu Province. Moreover, two allelic variants, Ile-1781-Leu and Trp-2027-Cys, have been identified in D. ciliaris var. chrysoblephara as conferring high-level resistance to metamifop (Cao et al. Reference Cao, Tao, Zhang, Gu, Li, Lou and Wang2023; Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023). Accordingly, it is necessary to investigate the resistance of D. ciliaris var. chrysoblephara to metamifop and cross-resistance patterns of different mutations in order to develop efficient and proactive weed management strategies for controlling this troublesome weed.
In this research, 53 D. ciliaris var. chrysoblephara populations that severely invaded direct-seeded rice fields were collected from Jiangsu Province in China. The objectives of the following study were to: (1) confirm and quantify the degree of metamifop resistance in different populations, (2) characterize the resistance mechanisms by surveying target-site mutations in ACCase genes of resistance-evolved populations, and (3) evaluate the cross-resistance patterns to herbicides with different MOAs in the resistant populations with specific ACCase mutations.
Materials and Methods
Sample Collection
Fifty-three D. ciliaris var. chrysoblephara populations severely infesting direct-seeded rice fields were sampled across Jiangsu Province in China in October 2022. Plants were sampled from fields with severe infestation of D. ciliaris var. chrysoblephara, and seeds from at least 30 mature plants from each field were pooled as a single population. Seeds of each population were stored in separate envelopes at room temperature until the end of seed dormancy. The susceptible (S) population was collected in a noncultivated area with no herbicide-use history in Yancheng, Jiangsu Province, China (33.71°N, 120.35°E) (Figure 1).
Figure 1. The occurrence of Digitaria ciliaris var. chrysoblephara in direct-seeded rice fields and location of a susceptible and 17 metamifop-resistant populations across Jiangsu Province, China, tested in this study.
Single-Dose Resistance Testing
Metamifop resistance of different D. ciliaris var. chrysoblephara populations was detected by a discriminating dosage of 60 g ai ha−1 (1/2-fold of the recommended dose), which can completely kill the S plants. Seeds were germinated at 28 to 30 C for 3 d, sown in square pots (7 by 7 by 8 cm) containing potting mix (50% organic matter and 50% vermiculite), and transplanted in a greenhouse with a temperature of 30 ± 2 C and a light/dark photoperiod of 14 h/10 h. The commercial formulation of metamifop was sprayed using a fan-nozzle laboratory sprayer cabinet delivering 300 L water ha−1 at 0.2 MPa on 3-leaf-stage plants. Approximately 12 to 14 seedlings per pot and four replicates were conducted for each population.
Seedling mortality of each population was calculated at 21 d after treatment (DAT). Populations of D. ciliaris var. chrysoblephara were defined as resistant (R) if more than 20% of plants in the population survived metamifop application, developing resistance (DR) if 1% to 20% of individuals survived metamifop, and susceptible (S) if less than 1% of individuals survived metamifop (Khammassi et al. Reference Khammassi, Hajri, Menchari, Chaabane and Souissi2019).
Dose Response to Metamifop
A total of 17 R populations and the S population were used for the whole-plant dose–response experiment on the basis of the initial single-dose resistance-screening results. The seedlings were foliar-treated with gradient doses of metamifop as described earlier when they reached the 2- to 3-leaf stage. The application dosages were 0X, 1/81X, 1/27X, 1/9X, 1/3X, and 1X doses of the recommended rate (120 g ai ha−1) for the S population and 0X, 1/9X, 1/3X, 1X, 3X, and 9X doses of the recommended rate for the R populations. At 21 DAT, the fresh weight of aboveground parts in each pot was measured. The experiment was conducted twice with three replicates for each treatment.
ACCase Partial Gene Sequencing
Survivors from metamifop resistance identification in the single-dose resistance-screening assays were frozen at −80 C and used for ACCase gene sequencing. Approximately 2 to 10 individual plants of each population were sequenced due to difference in survival rates (Supplementary Table S1). DNA was extracted using a Plant Genomic DNA Kit (Tiangen, Beijing, China) from the leaves of each D. ciliaris var. chrysoblephara plant. The amplification of a portion of the ACCase gene was conducted with previously reported primers (F: 5′-ATTAGGTGGATTATTGACTCTGTTG-3′; R: 5′-TCTGGGTCAAGCCTACCCAT-3′) (Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023), which covered all of the eight mutation sites conferring ACCase-inhibitor resistance in weeds. A polymerase chain reaction (PCR) was run using the following conditions: 4 min of denaturation at 95 C, 35 cycles of 95 C for 30 s, 58 C for 30 s, and 72 C for 2 min, and 10-min elongation at 95 C. The PCR product was directly sequenced by the Sanger method, and the ACCase gene sequence was visually checked with Chromas v. 2.3 (Technelysium, Helensvale, Australia).
Dose Response to Other Herbicides with Different MOAs
The YC07 (Ile-1781-Leu), YZ09 (Trp-2027-Cys), SQ03 (Trp-2027-Ser), and HA06 (Ile-2041-Asn) populations with different ACCase mutations were used for investigating the cross-resistance patterns to other herbicides. Ten herbicides, including six ACCase inhibitors, one acetolactate synthase (ALS) inhibitor, one protoporphyrinogen oxidase (PPO) inhibitor, one synthetic auxin herbicide, and one very-long-chain fatty-acid (VLCFA) inhibitor, were used for cross-resistance measurement by dose–response experiments as described earlier (Table 1). At 21 DAT, the fresh weight of aboveground parts was measured. Each experiment was conducted twice with three replicates.
Table 1. Herbicide information and application rates for dose–response experiments
a ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase; PPO, protoporphyrinogen oxidase; VLCFA, very-long-chain fatty-acid synthesis.
b EC, emulsifiable concentrate; EW, emulsion in water; GR, granules; SC, suspension concentrate; WDG, water-dispersible granule.
c X, the recommended dose of each herbicide.
Data Analysis
Dose–response curves were constructed using SigmaPlot v. 12.0 (Systat Software), and the herbicide dose causing 50% growth reduction (GR50) was calculated with a log-logistic model function (Equation 1) (Seefeldt et al. Reference Seefeldt, Jensen and Fuerst1995). In Equation 1, y is the percentage reduction of aboveground fresh weight, x is variable dose of each herbicide, and C and D are the lower and upper limits, respectively. The resistance index (RI) is expressed by GR50 values (R) versus GR50 values (S).
$$y = C + {{D - C} \over {1 + {{\left( {{x \over {{\rm{G}}{{\rm{R}}_{50}}}}} \right)}^b}}}$$
Results and Discussion
Resistance Status to Metamifop in Digitaria ciliaris var. chrysoblephara
Digitaria ciliaris var. chrysoblephara has been widely infesting rice fields, especially dry-seeded rice, across Jiangsu Province in China in recent years. Weed control of this species primarily relied on ACCase-inhibiting herbicides, and continuous metamifop selection pressure caused the rapid spread of herbicide resistance within rice fields (Cao et al. Reference Cao, Tao, Zhang, Gu, Li, Lou and Wang2023). For the current study, the metamifop sensitivity of 53 D. ciliaris var. chrysoblephara populations was first evaluated with a single-dose spraying. The screening results showed that 17 populations had evolved resistance (R) to metamifop, with a resistance frequency of 32.1%, and 5 populations were in the process of developing resistant (DR) to metamifop, accounting for 9.4% (Figure 1; Supplementary Table S1). Plants of the S population completely died at one-half of the recommended dose (60 g ai ha−1), with a GR50 value of 4.65 g ai ha−1 (Table 2; Supplementary Table S1). The GR50 values of the R populations ranged from 12.62 to 149.06 g ai ha−1, producing 2.7- to 32.1-fold resistance to metamifop (Table 2).
Table 2. Herbicide dose causing 50% growth reduction (GR50) and resistance index (RI) values for metamifop, identification of ACCase gene mutations, codon sequence, number of mutants versus number tested in the susceptible (S) and different resistant (R) Digitaria ciliaris var. chrysoblephara populations
Since the first case of reported metamifop-resistance of Digitaria spp. in rice fields in 2017 (Jiang et al. Reference Jiang, Chen and Dong2017), the frequency of resistance has continuously increased in China, especially in areas with extensive application of herbicides. The rapid development of resistance to metamifop in D. ciliaris var. chrysoblephara may be related to the following two factors. First of all, the risk of resistance is quite high for ACCase-inhibiting herbicides, suggesting a marked decrease in herbicide sensitivity will be observed in a relatively short period of time (Bagavathiannan et al. Reference Bagavathiannan, Norsworthy, Smith and Neve2014; Kaundun Reference Kaundun2014). Second, the Digitaria spp. had been reported resistant to diverse herbicides with different MOAs worldwide, including ACCase inhibitors, ALS inhibitors, and glyphosate, indicating these species were prone to develop resistance to herbicides (de Carvalho et al. Reference de Carvalho, Alves, González-Torralva, Cruz-Hipolito, Rojano-Delgado, De Prado, Gil-Humanes, Barro and de Castro2012; Laforest et al. Reference Laforest, Soufiane, Simard, Obeid, Page and Nurse2017; Li et al. Reference Li, Li, Gao and Fang2017; Takano et al. Reference Takano, Melo, Ovejero, Ovejero, Westra, Todd, Gaines and Dayan2020; Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023; Yanniccari et al. Reference Yanniccari, Vázquez-García, Gigón, Palma-Bautista, Vila-Aiub and De Prado2022; Zhao et al. Reference Zhao, Xu, Li, Qi, Huang, Hu, Wang and Liu2023). Due to a dilution effect by susceptible homoeologous gene copies, ACCase herbicide resistance evolves faster in grass weeds that contain only one or two ACCase gene copies, such as E. indica (Deng et al. Reference Deng, Li, Yao, Duan, Yang and Yuan2023a) and rigid ryegrass (Lolium rigidum Gaudin) (Yu et al. Reference Yu, Collavo, Zheng, Owen, Sattin and Powles2007), than in hexaploid wild oat (Avena fatua L.) (Yu et al. Reference Yu, Ahmad-Hamdani, Han, Christoffers and Powles2013) and E. crus-galli (Yang et al. Reference Yang, Yang, Zhang, Wang, Fu and Li2021), which contain of three and six ACCase copies, respectively. This helps to explain the rapid spread of metamifop resistance in D. ciliaris var. chrysoblephara in recent years.
ACCase Mutations in Resistant Digitaria ciliaris var. chrysoblephara
The sequence of a 1,088-bp fragment covering part of the ACCase gene was amplified from each D. ciliaris var. chrysoblephara plant using a PCR-based approach, and it exhibited more than 98% nucleotide identity with sequences deposited in GenBank (accession nos. OQ354339 and OQ354340). Because there were two ACCase genes in D. ciliaris var. chrysoblephara (Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023), double peaks were observed in specific single-nucleotide polymorphism sites between two gene copies. The sequencing results showed that all 10 plants from the S population have no mutations in ACCase genes. Four amino acid substitutions, Ile-1781-Leu, Trp-2027-Cys/Ser, and Ile-2041-Asn, were found in a single ACCase gene of different resistant populations (Table 2; Figure 2). Among these mutations, the Trp-2027-Cys was the most common ACCase mutation identified in resistant D. ciliaris var. chrysoblephara. A total of 78 plants in 7 R populations and 5 DR populations survived metamifop treatment, and these populations contained a Trp-2027-Cys mutation in the ACCase gene (Supplementary Table S1). Two nucleotide mutations, TGT and TGC, were detected in codon position 2027, and conferred the same amino acid substitution of Trp-2027-Cys (Figure 2). Second, the Ile-2041-Asn substitution occurred in plants survived from 8 R populations. Conversely, both Ile-1781-Leu and Trp-2027-Ser were detected in only one R population, YC07 and SQ03, respectively. Notably, ACCase gene mutations were detected in all of the R and DR populations, indicating that the target-based mechanism plays a key role in the resistance evolution to metamifop in D. ciliaris var. chrysoblephara.
Figure 2. The chromatograms of different ACCase mutations involving Ile-1781-Leu, Trp-2027-Cys, Trp-2027-Ser, and Ile-2041-Asn.
Allelic variants in ACCase genes are the most commonly reported TSR mechanisms and have been characterized as yielding resistance in different kinds of grass weeds, including Alopecurus spp. (Petit et al. Reference Petit, Bay, Pernin and Délye2010), American sloughgrass [Beckmannia syzigachne (Steud.) Fernald] (Tang et al. Reference Tang, Zhou, Zhang and Chen2015), Echinochloa spp. (Iwakami et al. Reference Iwakami, Ishizawa, Sugiura, Kashiwagi, Oga, Niwayama and Uchino2024), E. indica (Deng et al. Reference Deng, Li, Yao, Duan, Yang and Yuan2023a), L. chinensis (Deng et al. Reference Deng, Li, Yao, Wu, Zhu, Yang and Yuan2023b), and L. rigidum (Yu et al. Reference Yu, Collavo, Zheng, Owen, Sattin and Powles2007). For Digitaria spp., the Ile-1781-Leu and Trp-2027-Cys mutations have been reported to confer high-level resistance to ACCase-inhibiting herbicides in previous studies (Basak et al. Reference Basak, McElroy, Brown, Gonçalves, Patel and McCullough2020; Cao et al. Reference Cao, Tao, Zhang, Gu, Li, Lou and Wang2023; Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023). The other two mutations, Trp-2027-Ser and Ile-2041-Asn, were first reported in the ACCase of Digitaria spp. Although NTSR mechanisms were not investigated in the current study, P450-involved metabolism was determined to mediate ACCase resistance in certain populations in our previous paper (Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023). In addition, both TSR and NTSR mechanisms simultaneously participating in ACCase-inhibiting herbicide resistance have been identified in some other grass weed species (Golmohammadzadeh et al. Reference Golmohammadzadeh, Rojano-Delgado, Vázquez-García, Romano, Osuna, Gherekhloo and De Prado2020; Zhao et al. Reference Zhao, Ge, Yan, Bai, Wang, Liu and Wang2019, Reference Zhao, Jiang, Li, Gao, Zhang, Liao and Cao2022). Hence, although we focused on the target-site ACCase gene mutations in D. ciliaris var. chrysoblephara in this paper, non–target site enhanced metabolism resistance was not ruled out in these resistant populations.
Cross-Resistance Patterns of Specific Mutations to Different Herbicides
Four R populations, YC07, YZ09, SQ03, and HA06, which carried the target ACCase Ile-1781-Leu, Trp-2027-Cys, Trp-2027-Ser, and Ile-2041-Asn mutations, respectively, were used for determining cross-resistance profiles to other herbicides with different MOAs. The results showed that all four R populations exhibited cross-resistance to several specific ACCase inhibitors, but no resistance to the ALS inhibitor bispyribac-sodium, the PPO inhibitor pyraclonil, the synthetic auxin herbicide quinclorac, and the VLCFA inhibitor anilofos, indicating that D. ciliaris var. chrysoblephara developed exclusive resistance to ACCase herbicides in rice-cropping systems (Table 3). The whole-plant experiment indicated that the S plants died completely at the recommended dose of each ACCase inhibitor (Figure 3). All four R populations exhibited different levels of cross-resistance to cyhalofop-butyl, fenoxaprop-P-ethyl, haloxyfop-P-methyl, and pinoxaden, producing 10.0- to 19.9-fold, 53.7- to 132.8-fold, 6.2 to 62.6-fold, and 2.3- to 5.4-fold decreases in sensitivity compared with the S population, respectively (Table 3; Figure 3). In addition, the YC07 (Ile-1781-Leu) and HA06 (Ile-2041-Asn) populations were resistant to sethoxydim (RI = 13.2 and 5.7, respectively), and the YC07 population was resistant to clethodim (RI = 2.7) as well (Table 3; Figure 3). It should also be noted that none of the four herbicides with other MOAs could kill the S population if they were applied at rates below the recommended field dosage recommended (data not shown), suggesting these herbicides were unable to control this weed due to poor effectiveness.
Table 3. Sensitivity to different herbicides for the susceptible (S) and resistant (YC07, YZ09, SQ03, and HA06) Digitaria ciliaris var. chrysoblephara populations a
a GR50, herbicide dose causing 50% growth reduction; RI, resistance index.
Figure 3. Dose–response curves of the susceptible (S) and four resistant (R) (YC07, YZ09, SQ03, and HA06) Digitaria ciliaris var. chrysoblephara populations to different acetyl-CoA carboxylase (ACCase)-inhibiting herbicides: (A) cyhalofop-butyl, (B) fenoxaprop-P-ethyl, (C) haloxyfop-P-methyl, (D) clethodim, (E) sethoxydim, and (F) pinoxaden.
Based on the results, we concluded that the Ile-1781-Leu substitution conferred wide-spectrum resistance to all of the APP, CHD, and DEN herbicides tested, which is in line with previous research in other weed species (Basak et al. Reference Basak, McElroy, Brown, Gonçalves, Patel and McCullough2020; Deng et al. Reference Deng, Cai, Zhang, Chen, Chen, Di and Yuan2019; Petit et al. Reference Petit, Bay, Pernin and Délye2010; Yu et al. Reference Yu, Collavo, Zheng, Owen, Sattin and Powles2007). Ile-1781 is within a domain close to the binding site for ACCase herbicides across three chemical groups, explaining the resistance spectrum to all three families (Beckie and Tardif Reference Beckie and Tardif2012; Gaines et al. Reference Gaines, Duke, Morran, Rigon, Tranel, Küpper and Dayan2020). In contrast, two substitutions at codon position 2027, Trp-2027-Cys and Trp-2027-Ser, endowed resistance to the APP and DEN herbicides, but susceptibility to the CHD herbicides. Similar results were obtained in Trp-2027-Cys and Trp-2027-Ser mutant L. chinensis, which showed resistance to metamifop, cyhalofop-butyl, and fenoxaprop-P-ethyl (APPs), but no resistance to clethodim (CHD) (Jiang et al. Reference Jiang, Wang, Li Wei, Zhang, Liao, Zhao and Cao2022). Moreover, the HA06 population carrying an Ile-2041-Asn mutation was resistant to the APP herbicides, the DEN herbicide, and the CHD herbicide sethoxydim, but susceptible to the CHD herbicide clethodim. Accordingly, the ACCase mutations at amino acid positions 1781, 2027, and 2041 exhibited varied cross-resistance patterns to ACCase inhibitors.
In addition, the whole-plant bioassays showed poor control of D. ciliaris var. chrysoblephara with other postemergence herbicides registered for rice cropping, including bispyribac-sodium, pyraclonil, quinclorac, and anilofos. Thus far, in rice fields, few alternative herbicides can be used for controlling D. ciliaris var. chrysoblephara, except ACCase inhibitors. Our previous study reported that three preemergence herbicides, including pretilachlor, pendimethalin, and oxadiazon, could greatly inhibit the seed germination of this weed (Yang et al. Reference Yang, Zhu, Yang, Wei, Lv and Li2023). On the basis of this analysis, reasonable use of preemergence herbicides can greatly reduce the selection pressure of postemergence herbicides and thus mitigate the risk of ACCase-inhibiting herbicide resistance in D. ciliaris var. chrysoblephara. In combination with chemical control, agricultural and ecological measures, such as crop rotation, straw mulching, and depleting the weed seedbank, can effectively improve the biodiversity of agroecosystems and reduce the number of viable seeds in the soil (Zhang et al. Reference Zhang, Li, Zhao and Qiang2021; Zhu et al. Reference Zhu, Wang, DiTommaso, Zhang, Zheng, Liang, Islam, Yang, Chen and Zhou2020). Therefore, integrated approaches including chemical and nonchemical control can be employed to develop diverse and sustainable weed management strategies in cropping systems.
In conclusion, it is evident that the D. ciliaris var. chrysoblephara in direct-seeded rice fields has evolved resistance to metamifop in Jiangsu Province, China. Four ACCase mutations, Ile-1781-Leu, Trp-2027-Cys/Ser, and Ile-2041-Asn, were found in resistant D. ciliaris var. chrysoblephara plants, resulting in various cross-resistance profiles to ACCase herbicides. Few postemergence herbicides can be selected for controlling D. ciliaris var. chrysoblephara plants in rice cultivation except ACCase inhibitors, and this poses a huge challenge to weed management for farmers. Integrated weed management approaches need to be adopted to delay the resistance evolution in D. ciliaris var. chrysoblephara and promote sustainable development of agroecosystems.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/wsc.2024.30
Funding
This research was funded by the National Key Research and Development Program of China (grant no. 2023YFD1401100), the National Natural Science Foundation of China (grant no. 32372569 and 32072435), the Natural Science Foundation of Jiangsu Province (grant no. BK20231243), and the Yangzhou Modern Agricultural Fund (grant no. YZ2022048).
Competing interests
The authors declare no competing interests.
