Resistance Level and Metabolism of Barnyard-Grass (Echinochloa crusgalli (L.) Beauv.) Populations to Quizalofop-p-ethyl in Heilongjiang Province, China

A natural glutathione S-transferase gene GSTU23 confers metabolic resistance to metamifop in Echinochloa crus-galli

Herbicides are essential for farmers to control weed. However, prolonged use of herbicides has caused the development of herbicide resistance in weeds. Here, the resistant Echinochloa crus-galli (RL5) was obtained by continuous treatment with metamifop for five generations in paddy fields. RL5 plants showed a 13.7-fold higher resistance to metamifop compared to susceptible E. crus-galli (SL5) plants. Pre-treatment with GST inhibitor (NBD-Cl) significantly increased the susceptibility of RL5 plants to metamifop. Faster metamifop metabolism and higher GST activity in RL5 plants than in SL5 plants were also confirmed, highlighting the role of GST in metabolic resistance. RNA-Seq analysis identified EcGSTU23 as a candidate gene, and this gene was up-regulated in RL5 and field-resistant E. crus-galli plants. Furthermore, the EcGSTU23 gene was overexpressed in the transgenic EcGSTU23-Maize, and the EcGSTU23-Maize showed resistance to metamifop. In vitro metabolic studies also revealed that the purified EcGSTU23 displayed catalytic activity in glutathione (GSH) conjugation, and metamifop was rapidly metabolized in the co-incubation system containing EcGSTU23 protein. These results provide direct experimental evidence of EcGSTU23's involvement in the metabolic resistance of E. crus-galli to metamifop. Understanding the resistance mechanism can help in devising effective strategies to combat herbicide resistance and breeding of genetically modified herbicide resistant crops.

Cloning and functional characterization of a tau class glutathione transferase associated with haloxyfop-P-methyl resistance in Digitaria sanguinalis

BACKGROUND

Haloxyfop-P-methyl, an acetyl-CoA carboxylase (ACCase)-inhibiting herbicide, has been extensively used to control grass weeds. Widespread use of haloxyfop-P-methyl in cotton fields in China has led to the development of glutathione transferase (GST)-mediated resistance in Digitaria sanguinalis. An RNA-seq analysis identified DsGSTU1, a tau class glutathione transferase from the D. sanguinalis transcriptome as a potential candidate. Here, we cloned DsGSTU1 from D. sanguinalis young leaf tissues and subsequently characterized DsGSTU1 by a combination of sequence analysis, as well as functional heterologous expression in rice.

RESULTS

The full-length coding DNA sequence (CDS) of DsGSTU1 is 717 bp in length. Higher DsGSTU1 expression was observed in haloxyfop-P-methyl-resistant (HR) D. sanguinalis than in haloxyfop-P-methyl-susceptible (HS) plants. Overexpression of the DsGSTU1 gene was confirmed by transformation into the wild-type (WT) Nipponbare rice with pBWA(V)HS, a recombinant expression vector. GST activity in transgenic rice seedlings was 1.18-1.40-fold higher than the WT rice seedlings before and after haloxyfop-P-methyl treatment, respectively. Additionally, transgenic rice seedlings overexpressing DsGSTU1 were less sensitive to haloxyfop-P-methyl.

CONCLUSION

Our combined findings suggest that DsGSTU1 is involved in metabolic resistance to haloxyfop-P-methyl in D. sanguinalis. A better understanding of the major genes contributing to herbicide-resistant D. sanguinalis facilitates the development of resistance management strategies for this global invasive grass weed. © 2023 Society of Chemical Industry.

High aquaporin expression correlates with increased translocation of quinclorac from shoots to roots in resistant Echinochloa crus-galli var. zelayensis

BACKGROUND

Echinochloa crus-galli var. zelayensis is a troublesome weed in rice fields and can be controlled by using quinclorac. However, over-reliance on quinclorac has resulted in resistant (R) barnyardgrass, which differs significantly in its ability to transport quinclorac compared to susceptible (S) barnyardgrass. This study aimed to investigate the underlying mechanisms for this different translocation between R and S barnyardgrass.

RESULTS

Larger amount of quinclorac was transferred from shoots to roots in R compared to S barnyardgrass. After 1 day of quinclorac [300 g active ingredient (a.i.) ha^-1 ] foliar treatment, its content in shoots of R was 81.92% of that in S barnyardgrass; correspondingly, in roots of R was 1.17 fold of that in S barnyardgrass. RNA-sequencing and quantitative real-time polymerase chain reaction (qRT-PCR) confirmed the expression levels of PIPs belonging to aquaporins (AQPs) in R were higher than in S barnyardgrass, with or without quinclorac treatment. With co-application of quinclorac and AQPs inhibitors [mercury(II) chloride (HgCl₂ )] treatment, even though the expression levels of PIPs and the transport rates of quinclorac were both suppressed in R and S barnyardgrass, this process was less pronounced in R than in S barnyardgrass.

CONCLUSION

This report provides clear evidence that higher PIPs expression results in rapid quinclorac translocation from shoots to roots and reduces the quinclorac accumulation in the shoot meristems in R barnyardgrass, thus reducing the control efficacy of quinclorac. © 2022 Society of Chemical Industry.

First Asp-2078-Gly Mutation Conferring Resistance to Different ACCase Inhibitors in a Polypogon fugax Population from China

Asia minor bluegrass (Polypogon fugax) is a common and problematic weed throughout China. P. fugax that is often controlled by acetyl-CoA carboxylase (ACCase) inhibitors in canola fields. Herein, we confirmed a P. fugax population (R) showing resistance to all ACCase inhibitors tested with resistance indexes ranging from 5.4-18.4. We further investigated the resistance mechanisms of this R population. Molecular analyses revealed that an amino acid mutation (Asp-2078-Gly) was present in the R population by comparing ACCase gene sequences of the sensitive population (S). In addition, differences in susceptibility between the R and S population were unlikely to be related to herbicide metabolism. Furthermore, a new derived cleaved amplified polymorphic sequence (dCAPS) method was developed for detecting the Asp-2078-Gly mutation in P. fugax efficiently. We found that 93.75% of plants in the R population carried the Asp-2078-Gly mutation, and all the herbicide-resistant phenotype of this R population is inseparable from this mutation. This is the first report of cross resistance to ACCase inhibitors conferred by the Asp-2078-Gly target-site mutation in P. fugax. The research suggested the urgent need to improve the diversity of weed management practices to prevent the widespread evolution of herbicide resistance in P. fugax in China.

Identification and Comprehensive Evaluation of Resistant Weeds Using Unmanned Aerial Vehicle-Based Multispectral Imagery

Atrazine is one of the most widely used herbicides in weed management. However, the widespread use of atrazine has concurrently accelerated the evolution of weed resistance mechanisms. Resistant weeds were identified early to contribute to crop protection in precision agriculture before visible symptoms of atrazine application to weeds in actual field environments. New developments in unmanned aerial vehicle (UAV) platforms and sensor technologies promote cost-effective data collection by collecting multi-modal data at very high spatial and spectral resolution. In this study, we obtained multispectral and RGB images using UAVs, increased available information with the help of image fusion technology, and developed a weed spectral resistance index, WSRI = (RE-R)/(RE-B), based on the difference between susceptible and resistant weed biotypes. A deep convolutional neural network (DCNN) was applied to evaluate the potential for identifying resistant weeds in the field. Comparing the WSRI introduced in this study with previously published vegetation indices (VIs) shows that the WSRI is better at classifying susceptible and resistant weed biotypes. Fusing multispectral and RGB images improved the resistance identification accuracy, and the DCNN achieved high field accuracies of 81.1% for barnyardgrass and 92.4% for velvetleaf. Time series and weed density influenced the study of weed resistance, with 4 days after application (4DAA) identified as a watershed timeframe in the study of weed resistance, while different weed densities resulted in changes in classification accuracy. Multispectral and deep learning proved to be effective phenotypic techniques that can thoroughly analyze weed resistance dynamic response and provide valuable methods for high-throughput phenotyping and accurate field management of resistant weeds.

Increasing the value and efficiency of herbicide resistance surveys

The scale of herbicide resistance within a cropping region can be estimated and monitored using surveys of weed populations. The current approach to herbicide resistance surveys is time-consuming, logistically challenging and costly. Here we review past and current approaches used in herbicide resistance surveys with the aims of (i) defining effective survey methodologies, (ii) highlighting opportunities for improving efficiencies through the use of new technologies and (iii) identifying the value of repeated region-wide herbicide resistance surveys. One of the most extensively surveyed areas of the world's cropping regions is the Australian grain production region, with >2900 fields randomly surveyed in each of three surveys conducted over the past 15 years. Consequently, recommended methodologies are based on what has been learned from the Australian experience. Traditional seedling-based herbicide screening assays remain the most reliable and widely applicable method for characterizing resistance in weed populations. The use of satellite or aerial imagery to plan collections and image analysis to rapidly quantify screening results could complement traditional resistance assays by increasing survey efficiency and sampling accuracy. Global management of herbicide-resistant weeds would benefit from repeated and standardized surveys that track herbicide resistance evolution within and across cropping regions. © 2021 Society of Chemical Industry.

Quizalofop-p-ethyl resistance in Polypogon fugax involves glutathione S-transferases

BACKGROUND

Asia minor bluegrass (Polypogon fugax) is one of the main weeds invading Chinese canola fields. The P. fugax resistant population SC-R, which survived quizalofop-p-ethyl at the field-recommended rate (67.5 g ha^-1 ), was collected from a canola field in Qingsheng County in China. The present study aimed to (1) characterize the SC-R resistance pattern to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides, and (2) investigate the mechanism of quizalofop-p-ethyl resistance in this population.

RESULTS

Dose-response studies showed that resistance to quizalofop-p-ethyl and haloxyfop occurred in the SC-R population. Four transcripts/genes encoding the plastidic ACCase carboxyl-transferase domain were isolated from the P. fugax plants. No mutations in the four ACCase genes were detected in the SC-R population compared to the SC-S population. Pre-treatment with the known glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBDCl), reversed resistance to quizalofop-p-ethyl and partially reversed resistance to haloxyfop-R-methyl in the resistant population (SC-R). However, the cytochrome P450 inhibitor malathion did not reverse the resistance. There was no difference in basal GST activity (using CDNB as a substrate), but there was higher inducible GST activity in SC-R relative to SC-S. Two GST genes, GST2c and GSTL3, were constitutively overexpressed in the resistant SC-R population.

CONCLUSION

This study confirmed that resistance to quizalofop-p-ethyl in the resistant P. fugax population is likely nontarget-site based involving GST, and this resistance mechanism also partially confers haloxyfop-R-methyl resistance. © 2020 Society of Chemical Industry.

Cross-resistance mechanisms to ACCase-inhibiting herbicides in short-spike canarygrass (Phalaris brachystachys)

Herbicides that inhibit acetyl-coenzyme A carboxylase (ACCase) are commonly used to control weedy grasses such as short-spike canarygrass (Phalaris brachystachys). Two resistant biotypes of P. brachystachys (R1 and R2) were found in different winter wheat fields in Iran. This study was done to confirm the suspected resistance observed in the field and to elucidate the resistance mechanisms involved. The results indicated that the both resistant biotypes showed cross-resistance to diclofop-methyl (DM), pinoxaden (PN) and cycloxydim (CD) herbicides. Based on the herbicide dose that inhibited 50% of the ACCase activity (I₅₀), the ACCase activity of the resistant biotypes was less sensitive than the S biotype to DM, CD, and PN. No differences in translocation were detected between biotypes; most of the herbicide remained in the treated leaves. The ¹⁴C-DM metabolites were identified using thin-layer chromatography. Pre-treatment with the cytochrome P450 inhibitor ABT inhibited ¹⁴C-DM metabolism in the R1 biotype, indicating that metabolism is involved in the DM resistance in the R1 biotype. DNA sequencing studies found an Ile-1781-Thr change in both resistant biotypes, conferring cross-resistance to ACCase inhibitors. In general, in the R1 biotype which showed a higher level of resistance than that of the R2 biotype, cross-resistance was observed because of mutation and DM metabolism, while in the R2 biotype, the mutation confers resistance to ACCase-inhibiting herbicides. This is the first reported evidence of the mechanisms responsible for the resistance to ACCase herbicides in P. brachystachys. These results could be useful for improved management of resistant biotypes carrying similar mutations.

Non-Target-Site Resistance to Herbicides: Recent Developments

Non-target-site resistance (NTSR) to herbicides in weeds can be conferred as a result of the alteration of one or more physiological processes, including herbicide absorption, translocation, sequestration, and metabolism. The mechanisms of NTSR are generally more complex to decipher than target-site resistance (TSR) and can impart cross-resistance to herbicides with different modes of action. Metabolism-based NTSR has been reported in many agriculturally important weeds, although reduced translocation and sequestration of herbicides has also been found in some weeds. This review focuses on summarizing the recent advances in our understanding of the physiological, biochemical, and molecular basis of NTSR mechanisms found in weed species. Further, the importance of examining the co-existence of TSR and NTSR for the same herbicide in the same weed species and influence of environmental conditions in the altering and selection of NTSR is also discussed. Knowledge of the prevalence of NTSR mechanisms and co-existing TSR and NTSR in weeds is crucial for designing sustainable weed management strategies to discourage the further evolution and selection of herbicide resistance in weeds.

Basis of ACCase and ALS inhibitor resistance in Hordeum glaucum Steud

BACKGROUND

Acetyl coenzyme-A carboxylase (ACCase) and/or acetolactate synthase (ALS) inhibitor resistance has been identified by herbicide resistance screening in eight populations obtained from cropping regions of South Australia. This study aimed to quantify the level of resistance and characterise the molecular basis of resistance to ACCase and ALS inhibitors in these H. glaucum populations.

RESULTS

H. glaucum populations from the Upper-North region were highly resistant (resistance index RI > 12) to the aryloxyphenoxypropionate (APP) herbicides quizalofop and haloxyfop and less resistant (RI = 2-12) to cyclohexanedione (CHD) herbicide clethodim, and some Mid-North populations had a low level of resistance (RI = 2-6) to the sulfonylurea (SU) herbicide mesosulfuron. Gene sequencing confirmed the presence of Ile-1781-Leu, Ile-2041-Asn and Gly-2096-Ala mutations in the ACCase gene, with no mutation found in the ALS gene. The use of the known metabolic inhibitor malathion in combination with mesosulfuron enhanced the activity of this herbicide. These populations were also susceptible to SU herbicide sulfometuron.

CONCLUSION

This study has documented APP-to-CHD herbicide cross-resistance, the first case of ACCase inhibitor resistance due to Ile-2041-Asn mutation, and characterised the resistance to ALS inhibitors in H. glaucum. Resistance to ACCase inhibitors is due to a target-site mutation. The reversal of SU resistance by malathion and susceptibility to sulfometuron suggests that non-target-site mechanisms confer resistance to ALS inhibitors. © 2016 Society of Chemical Industry.