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Background: We have previously demonstrated that an aldo‐keto reductase (AKR) from Echinochloa colona (EcAKR4‐1) can metabolize glyphosate and confers glyphosate resistance. This study aims to investigate if the EcAKR4‐1 orthologs from Lolium rigidum also play a role in glyphosate resistance in non‐target‐site based, glyphosate‐resistant (R) L. rigidum populations from Western Australia. Results: The full‐length L. rigidum AKR gene (LrAKR4C10) orthologous to EcAKR4‐1, together with a distinct LrAKR1, were cloned from plants of a glyphosate‐susceptible (S) (VLR1) and three glyphosate R L. rigidum populations (WALR50, WALR60 and WALR70). Reverse transcription quantitative polymerase chain reaction (RT‐qPCR) results showed that basal expression levels of the two LrAKR genes did not differ between the R and S populations, but their expression was significantly induced by glyphosate (up to 4.3‐fold) or 2,4‐D treatment (up to 3.4‐fold) in R populations. Escherichia coli cells transformed respectively with LrAKR4C10 and LrAKR1 were more tolerant to glyphosate. Rice (Oryza sativa) seedlings overexpressing each of the two LrAKR gene survived glyphosate rates that were lethal to the green fluorescence protein (GFP) control plants. Structural modeling predicts a similar way of glyphosate binding and detoxification by LrAKR4C10 and EcAKR4‐1, but an alternative way of glyphosate binding by LrAKR1. Relatively lower capacity of the two LrAKRs in conferring glyphosate resistance than the known EcAKR4‐1 was discussed in relation to structural interaction. Conclusion: Glyphosate‐induced higher expression of the two LrAKR genes in L. rigidum populations contributes to a moderate level of glyphosate resistance likely through enhanced glyphosate metabolism. The herbicide 2,4‐D can also induce the LrAKR expression, indicating the potential antagonistic effect of 2,4‐D to glyphosate. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: Eleusine indica (L.) Gaertn. (goosegrass) is a major weed in global cropping systems. It has evolved resistance to glyphosate due to single Pro‐106‐Ser (P106S) or double Thr‐102‐Ile + Pro‐106‐Ser (TIPS) EPSPS target site mutations. Here, experiments were conducted to evaluate the single effect of soybean competition and its combined effect with a glyphosate field dose (1080 g ae ha−1) on the growth and fitness of plants carrying these glyphosate resistance endowing target site mutations. RESULTS: TIPS E. indica plants are highly glyphosate‐resistant but the double mutation endows a substantial fitness cost. The TIPS fitness penalty increased under the effect of soybean competition resulting in a cost of 95%, 95% and 96% in terms of, respectively, vegetative growth, seed mass and seed number investment. Glyphosate treatment of these glyphosate‐resistant TIPS plants showed an increase in growth relative to those without glyphosate. Conversely, for the P106S moderate glyphosate resistance mutation, glyphosate treatment alone reduced survival rate, vegetative growth, aboveground biomass (34%), seed mass (48%) and number (52%) of P106S plants relative to the glyphosate nontreated plants. However, under the combined effects of both soybean competition and the field‐recommended glyphosate dose, vegetative growth, aboveground biomass, seed mass and number of P106S and TIPS plants were substantially limited (by ≤99%). CONCLUSION: The ecological environment imposed by intense competition from a soybean crop sets a significant constraint for the landscape‐level increase of both the E. indica single and double glyphosate resistance mutations in the agroecosystem and highlights the key role of crop competition in limiting the population growth of weeds, whether they are herbicide‐resistant or susceptible. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND Trifluralin is widely used in Australia as one of the important pre‐emergence herbicides to control annual ryegrass (Lolium rigidum Gaud.) populations. Trifluralin resistance evolution and mechanisms have been identified in some ryegrass populations. RESULTS: In this study, 21 putative resistant field survey populations from Western Australian were screened with trifluralin, and 90% (19 of 21) contained individuals surviving 480 g ha−1 trifluralin treatment. Twelve populations contained individuals possessing the known α‐tubulin resistance mutations at Val‐202, Thr‐239 and Arg‐243 in TUA4 (alpha‐tubulin 4 n), plus multiple potential resistance mutations in TUA4 pending genetic confirmation. Three populations had only individuals carrying newly identified (but uncharacterized) mutations in TUA3/TUA4. Radioactive work found that six populations evolved metabolic resistance to trifluralin, and at least four of them also possessed the known and/or putative target‐site mutations. CONCLUSION: These results confirm that a high incidence of resistance to the dinitroaniline herbicide (trifluralin) is present, and target‐site tubulin mutations make a major contribution to resistance in these annual ryegrass populations. Co‐evolution of both target‐site and non‐target‐site resistance to per‐emergence herbicides warrants diverse management tactics. [ABSTRACT FROM AUTHOR]

BACKGROUND Tubulin, the target site of dinitroaniline herbicides, is encoded by small gene families in plants. To better characterize the mechanisms of target‐site resistance to dinitroaniline herbicides in the globally important weedy species Lolium rigidum, attempts were made to amplify and sequence α‐tubulin transcripts. RESULTS: Four α‐tubulin isoforms (TUA1, TUA2, TUA3 and TUA4) were identified in L. rigidum. Variations in the number and sequence of transcripts encoding these α‐tubulin proteins were found in individuals from the two L. rigidum populations examined. Within and among populations, differences in the 5′‐ and 3′‐untranslated regions of cDNA in TUA3 and TUA4 were identified. Furthermore, a novel double mutation, Arg‐390‐Cys+Asp‐442‐Glu, in the TUA3 transcript was identified and has the potential to confer dinitroaniline resistance. CONCLUSION: This research reveals the complexity of the α‐tubulin gene family in individuals/populations of the cross‐pollinated weedy species L. rigidum, and highlights the need for better understanding of the molecular architecture of tubulin gene families for detecting resistance point mutations. Although TUA4 is a commonly expressed α‐tubulin isoform containing most frequently reported resistance mutations, other mutant tubulin isoforms may also have a role in conferring dinitroaniline resistance. [ABSTRACT FROM AUTHOR]

BACKGROUND Barnyardgrass (Echinochloa spp.) is a global weed in rice fields. Quinclorac is commonly used to control barnyardgrass. However, due to persistent use, quinclorac resistance has evolved. We obtained quinclorac‐susceptible (QS) and ‐resistant (QR1, QR2) lines from the progeny of a single resistant E. crus‐pavonis for a resistance mechanism study. RESULTS: Line QR1 exhibited resistance to high quinclorac rates (up to 6400 g ha−1), whereas line QR2 exhibited a resistance/susceptibility segregation ratio of 3:1 at the field or lower rates (400, 100 g ha−1). Intriguingly, a lower level of 14C‐quinclorac metabolism and hence a higher level of 14C‐quinclorac translocation was observed in QR1 than QS plants. The basal expression levels of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase (ACS) and ACC oxidase 2 (ACO2) genes did not differ significantly between the QR1 and QS lines. However, more expression of ACS and ACO genes was induced by quinclorac treatment in QS than in QR1. Basal levels of β‐cyanoalanine synthase (β‐CAS) gene expression were similar in QS and QR1 plants, but a greater level of down‐regulation was detected in QS than in QR1 plants after quinclorac treatment. CONCLUSION: These results indicate QR plants are less responsive to quinclorac than QS plants in terms of up‐regulating quinclorac metabolism and ethylene synthesis. Resistance in this E. crus‐pavonis line is likely controlled by a single major gene, involving possibly an alteration in auxin signal perception/transduction to the ethylene biosynthesis pathway. The β‐CAS is unlikely to play a major role in quinclorac resistance in this particular population. [ABSTRACT FROM AUTHOR]

BACKGROUND The photosystem II (PSII)‐inhibiting herbicides are important for Australian farmers to control Lolium rigidum Gaud. and other weed species in trazine tolerant (TT)‐canola fields. A L. rigidum population (R) collected from a TT‐canola field from Western Australia showed multiple resistance to PSII, acetyl‐coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors. The mechanisms of multiple resistance in this R population were determined. RESULTS: The R population showed a low‐level (about 3.0‐fold) resistance to the PSII‐inhibiting herbicides metribuzin and atrazine. Sequencing of the psbA gene revealed no differences between the R and susceptible (S) sequences. Furthermore, [14C]‐metribuzin experiments found no significant difference in metribuzin foliar uptake and translocation between the R and S plants. However, [14C]‐metribuzin metabolism in R plants was 2.3‐fold greater than in S plants. The cytochrome P450 monooxygenase inhibitor piperonyl butoxide (PBO) enhanced plant mortality response to metribuzin and atrazine in both R and S populations. In addition, multiple resistance to ALS and ACCase inhibitors are due to known resistance mutations in ALS and ACCase genes. CONCLUSION: The results demonstrate that enhanced metribuzin metabolism likely involving cytochrome P450 monooxygenase contributes to metribuzin resistance in Lolium rigidum. This is the first report of metabolic resistance to the PSII‐inhibiting herbicide metribuzin in Australian Lolium rigidum. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: A Lolium rigidum population collected from Western Australia was previously reported as highly resistant to dinitroaniline herbicides mainly due to a Val‐202‐Phe substitution in the target site α‐tubulin protein. To further determine the contribution of the 202 mutation to resistance, two sub‐populations, respectively comprising the 202 mutant and wild‐type (WT) individuals, were isolated from within the same resistant population and subject to dinitroaniline herbicide doses. A rice transgenic study was conducted to demonstrate whether the amino acid substitution at the 202 residue confers resistance. In addition, as indicated in the phenotyping and genotyping study, non‐target enhanced trifluralin metabolism was further examined in the same population. RESULTS: The 202 mutants were more resistant than the wild‐type plants. Rice calli transformed with the L. rigidum mutant α‐tubulin gene (Val‐202‐Phe) were more resistant to dinitroaniline herbicides relative to calli transformed with the wild‐type gene. Also, enhanced trifluralin metabolism was detected in the 202 mutants in comparison to the susceptible seedlings. CONLCUSION: Both target‐site Val‐202‐Phe α‐tubulin mutation and non‐target‐site enhanced trifluralin metabolism co‐exist in this dinitroaniline‐resistant L. rigidum population. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Weed resistance to foliar herbicides has dramatically increased worldwide in the last two decades. As a consequence, current practices of weed management have changed, with an increased adoption of soil‐applied herbicides to restore control of herbicide‐resistant weeds. We foresee metabolism‐based resistance and cross‐resistance to soil‐applied herbicides as a potential global consequence to the increased and widespread adoption of new and old soil‐applied herbicides. Thus, the aim of this study is to use computer simulation modelling to quantify and rank the risk of weeds evolving resistance to soil‐applied herbicides under different usage strategies (single herbicide use, rotations and mixtures) and population genetic hypotheses. RESULTS: Simulations indicate that without rotation it takes twice as long to select for resistance to a particular soil‐applied herbicide – trifluralin – than to any other herbicide option considered. Relative to trifluralin‐only use, simple herbicide rotation patterns have no effect in delaying resistance, whereas more complex rotation patterns can delay resistance two‐ or three‐fold. Herbicide mixtures further delay resistance up to six‐fold in comparison to single use or simple herbicide rotations. CONCLUSION: By computer modelling simulations we demonstrate that mixtures maximize herbicide effectiveness and the selection heterogeneity of soil‐applied herbicides, and delay herbicide resistance evolution in weedy plants. Our study is consistent with previous state‐of‐art scientific evidence (i.e. epidemiological and modelling studies across different systems and pests) and extension efforts (i.e. 'rotate herbicide mixtures') to provide insight to manage the selection and evolution of weed resistance. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Wild radish (Raphanus raphanistrum) is a globally important weed of crops. Two atrazine‐resistant wild radish populations (R1 and R2), collected from the Western Australia grain belt, were investigated for resistance to photosystem II (PSII) herbicides. RESULTS: Sequencing of the full‐length psbA gene revealed the well‐known Ser264–Gly substitution in population R1, whereas population R2 displayed a novel Phe274–Val substitution. Herbicide dose–response studies confirmed that the population with the Ser264–Gly mutation exhibited high‐level resistance to atrazine, but super‐sensitivity to bromoxynil. Plants possessing the novel Phe274–Val mutation exhibited a modest level of resistance to atrazine, metribuzin and diuron, and were bromoxynil susceptible. Structural modelling of the mutant D1 proteins predicts that the Ser264–Gly mutation endows atrazine resistance by abolishing H‐bonds, but confers bromoxynil super‐sensitivity by enhancing hydrogen bonding. The Phe274–Val substitution provides resistance to atrazine and diuron by indirectly affecting H‐bond formation between the Ser264 residue and the herbicides. CONCLUSION: The results demonstrate that the Phe274–Val mutation is likely responsible for resistance to PSII‐inhibiting triazine and urea herbicides. To our knowledge, this is the first evidence of the psbA Phe274–Val mutation in wild radish conferring resistance to PSII herbicides. © 2018 Society of Chemical Industry This study identifies a novel psbA Phe274–Val mutation conferring photosystem II (PSII) herbicide resistance. Structural modelling predicts that this mutation endows resistance by reducing H‐bonds between herbicides and the D1 protein. [ABSTRACT FROM AUTHOR]

BACKGROUND Organophosphate insecticides can inhibit specific cytochrome P450 enzymes involved in metabolic herbicide resistance mechanisms, leading to synergistic interactions between the insecticide and the herbicide. In this study we report synergistic versus antagonistic interactions between the organophosphate insecticide phorate and five different herbicides observed in a population of multiple herbicide-resistant Lolium rigidum. RESULTS Phorate synergised with three different herbicide modes of action, enhancing the activity of the ALS inhibitor chlorsulfuron (60% LD50 reduction), the VLCFAE inhibitor pyroxasulfone (45% LD50 reduction) and the mitosis inhibitor trifluralin (70% LD50 reduction). Conversely, phorate antagonised the two thiocarbamate herbicides prosulfocarb and triallate with a 12-fold LD50 increase. CONCLUSION We report the selective reversal of P450-mediated metabolic multiple resistance to chlorsulfuron and trifluralin in the grass weed L. rigidum by synergistic interaction with the insecticide phorate, and discuss the putative mechanistic basis. This research should encourage diversity in herbicide use patterns for weed control as part of a long-term integrated management effort to reduce the risk of selection of metabolism-based multiple herbicide resistance in L. rigidum. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Rice is a major field crop of paramount importance for global food security. However, the increased adoption of more profitable and resource-efficient direct-seeded rice ( DSR) systems has contributed to greater weed infestations, including weedy rice, which has become a severe problem in several Asian regions. In this study we have developed a conceptually novel method to protect rice plants at high doses of clomazone and triallate. RESULTS The insecticide phorate applied to rice seeds provided a substantial level of protection against the herbicides clomazone or triallate. A quantity of 15 kg phorate ha−1 significantly increased the LD50 values, which were more than twofold greater than for rice plants treated only with clomazone. A quantity of 20 kg phorate ha−1 in combination with 2000 g triallate ha−1 safened rice plants (80% survival) with LD50 >3.4-fold greater than in phorate-untreated rice. Weed control efficacy was not lowered by the presence of phorate-treated rice seeds. CONCLUSION Weedy rice is one of the most damaging global weeds and a major threat to DSR systems. In this study we have developed a proof-of-concept method to allow selective weedy rice control in rice crops. We call for herbicide discovery programmes and research to identify candidate safener and herbicide combinations to achieve selective herbicide control of weedy rice and alleviate weed infestations in global rice crops. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Weeds can be a greater constraint to crop production than animal pests and pathogens. Pre-emergence herbicides are crucial in many cropping systems to control weeds that have evolved resistance to selective post-emergence herbicides. In this study we assessed the potential to evolve resistance to the pre-emergence herbicides prosulfocarb + S-metolachlor or pyroxasulfone in 50 individual field Lolium rigidum populations collected in a random survey in Western Australia prior to commercialisation of these pre-emergence herbicides. RESULTS This study shows for the first time that in randomly collected L. rigidum field populations the selection with either prosulfocarb + S-metolachlor or pyroxasulfone can result in concomitant evolution of resistance to both prosulfocarb + S-metolachlor and pyroxasulfone after three generations. CONCLUSIONS In the major weed L. rigidum, traits conferring resistance to new herbicides can be present before herbicide commercialisation. Proactive and multidisciplinary research (evolutionary ecology, modelling and molecular biology) is required to detect and analyse resistant populations before they can appear in the field. Several studies show that evolved cross-resistance in weeds is complex and often unpredictable. Thus, long-term management of cross-resistant weeds must be achieved through heterogeneity of selection by effective chemical, cultural and physical weed control strategies that can delay herbicide resistance evolution. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND When applied at the correct plant stage and dose, herbicides are highly toxic to plants. At reduced, low herbicide doses (below the recommended dose) plants can survive and display continuous and quantitative variation in dose-survival responses. Recurrent (directional) selection studies can reveal whether such a phenotypic variation in plant survival response to low herbicide dose is heritable and leads to herbicide resistance. In a common experimental garden study, we have subjected a susceptible population of self-pollinated hexaploid Avena fatua to low-dose recurrent selection with the ACCase-inhibiting herbicide diclofop-methyl for three consecutive generations. RESULTS Significant differences in response to low-dose diclofop-methyl selection were observed between the selected progenies and parent plants, with a twofold diclofop-methyl resistance and cross-resistance to ALS-inhibiting herbicides. Thus, the capacity of self-pollinated A. fatua to respond to low-dose herbicide selection is marginal, and it is much lower than in cross-pollinated L. rigidum. Lolium rigidum in the same experiment evolved 40-fold diclofop-methyl resistance by progressive enrichment of quantitative resistance-endowing traits. CONCLUSION Cross-pollination rate, genetic variation and ploidy levels are identified as possible drivers affecting the contrasting capacity of Avena versus Lolium plants to respond to herbicide selection and the subsequent likelihood of resistance evolution at low herbicide dose usage. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Lolium rigidum populations in Australia and globally have demonstrated rapid and widespread evolution of resistance to acetyl coenzyme A carboxylase ( ACCase)-inhibiting and acetolactate synthase ( ALS)-inhibiting herbicides. Thirty-three resistant L. rigidum populations, randomly collected from crop fields in a most recent resistance survey, were analysed for non-target-site diclofop metabolism and all known target-site ACCase gene resistance-endowing mutations. RESULTS The HPLC profile of [ 14C]-diclofop-methyl in vivo metabolism revealed that 79% of these resistant L. rigidum populations showed enhanced capacity for diclofop acid metabolism (metabolic resistance). ACCase gene sequencing identified that 91% of the populations contain plants with ACCase resistance mutation(s). Importantly, 70% of the populations exhibit both non-target-site metabolic resistance and target-site ACCase mutations. CONCLUSIONS This work demonstrates that metabolic herbicide resistance is commonly occurring in L. rigidum, and coevolution of both metabolic resistance and target-site resistance is an evolutionary reality. Metabolic herbicide resistance can potentially endow resistance to many herbicides and poses a threat to herbicide sustainability and thus crop production, calling for major research and management efforts. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND This study confirms and characterises glyphosate resistance in two polyploid Echinochloa colona populations from north-eastern Australia. RESULTS Glyphosate dose response revealed that the two resistant populations were marginally (up to twofold) resistant to glyphosate. Resistant plants did not differ in non-target-site foliar uptake and translocation of 14C-glyphosate, but contained the known target-site 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS) mutation Pro-106-Thr and/or Pro-106-Leu. Although plants carrying either a single or two EPSPS mutations were glyphosate resistant relative to the susceptible population, they were still controlled at the field rate of glyphosate (450 g a.e. ha−1) when treated under warm conditions (25/20 °C). However, when treated in hot conditions (35/30 °C), most mutant resistant plants (68%) can survive the field rate, and an increase (2.5-fold) in glyphosate LD50 was found for both the R and S populations. CONCLUSIONS This study shows that one or two EPSPS Pro-106 mutations are insufficient to confer field-rate glyphosate resistance in polyploidy E. colona at mild temperatures. However, control of these mutant plants at the glyphosate field rate is poor at high temperatures, probably owing to reduced glyphosate efficacy. Therefore, glyphosate should be applied during relatively mild (warm) temperature periods in the summer growing season to improve E. colona control. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]