Evolution Of Herbicide Resistance Research Articles

Early adopter insights on physical impact mill technology for harvest weed seed control in Canada

The evolution and spread of herbicide resistance among the weed community has increased interest in alternative weed management strategies such as harvest weed seed control. Western Canadian producers have begun adopting physical impact mills as an additional weed management strategy. A survey of early adopters of physical impact mill technology in Canada was conducted to better understand the motivations behind producers adopting, initial experiences, and research needs. Ten producers responded to the survey, accounting for 18 out of an estimated 30 impact mills in use in Canada, believed to be located primarily in the Canadian Prairies. These producers were mainly from larger farms (> 4,000 ha), equipped the majority of their combines (75% average) and used the mills in essentially all crops grown. The majority of respondents were located in Saskatchewan, with 2 mills being used in Alberta. Wild oat (60%) and kochia (50%) were the weeds most frequently mentioned as specific motivators of impact mill adoption. Average increased fuel cost from the mill was estimated at CAD $3.46 ha-1, with average annual maintenance costs of about $1,500 per impact mill. Producers relied on information from mill companies and other early-adopting farmers primarily, followed by extension talks and social media. Research needs were also identified by producers that could inform the future direction of harvest weed seed control research in Canada. Future research should focus on confirming efficacy, optimizing combine settings, and looking at integrated systems with precision agriculture technologies.

Effects of Bipolaris yamadae strain HXDC-1-2 as a bioherbicide against Echinochloa crus-galli in rice and dry fields.

Barnyardgrass (Weed Science Society of America recommended) or Barnyard grass (Britannica recommended) (Echinochloa crus-galli (L.) P. Beauv.) is one of the most problematic and dominant weeds in world agricultural systems, especially in paddy fields, where tillering and grain yield can be reduced by 50-70% because of its competitive pressure. The frequent use of chemical herbicides to control E. crus-galli has led to the evolution of herbicide resistance. Developing bioherbicides using pathogenic fungi to control E. crus-galli could be an alternative option. In a previous study we showed that a strain of Bipolaris yamadae (HXDC-1-2) was promising in controlling gramineous weeds. Here we present a study that evaluated this fungus as a mycoherbicide against E. crus-galli in greenhouse and paddy fields, characterized mycelium growth and conidial production, and examined the infection development. The median effective dose (ED50) and 90% effective dose (ED90) values of microcapsulated B. yamadae strain HXDC-1-2 on E. crus-galli in the greenhouse were 7.17 × 102 and 9.35 × 103 conidia mL-1, respectively. Conidial germination, mycelial growth, and attachment formation occurred on E. crus-galli leaves within 1 to 6 h. The hyphae directly invaded cells and stomata, primarily from the appressorium on the epidermis, and necrotic lesions were observed on the leaf surface within 20 to 24 h. Applied to E. crus-galli plants at 1 × 105 conidia mL-1, the fungus reduced the weed's fresh weight of 75%. B. yamadae strain HXDC-1-2 has the potential to be developed as a bioherbicide against E. crus-galli plants, especially in rice fields. © 2024 Society of Chemical Industry.

Palmer amaranth (Amaranthus palmeri S. Wats.) and waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) biovigilance in Canadian Agro-ecosystems

The evolution and spread of herbicide-resistant weeds threatens long-term sustainability of Canadian agro-ecosystems. Herbicide-resistant weeds increase management inputs and costs, increase off-target and environmental exposure to pesticides, reduce yield quality and quantity, and impede harvest efficiency. Amaranthus species including Palmer amaranth ( Amaranthus palmeri S. Wats.) and waterhemp ( Amaranthus tuberculatus (Moq.) J.D. Sauer) are particularly concerning due to both their propensity towards herbicide resistance evolution, their history of invasion, and their spread in agro-ecosystems. A biovigilance approach is taken to build awareness of these pigweeds' initial invasion and spread in the USA. Characteristics of their identification, potential hybridization, and known herbicide resistance evolution are reviewed. Fourteen species of Amaranthus are found in Canada, nine of which (including waterhemp) possess herbicide-resistant biotypes. A total of 45 hybrids between various Canadian Amaranthus species with each other or Palmer amaranth have been noted. Hybrids have been experimentally produced or observed from herbarium specimens, with three cases of herbicide resistance transfer notably with Palmer amaranth or waterhemp. Mitigation strategies will depend on successful species identification and herbicide resistance status determination. Common pathways for Palmer amaranth introductions in the northern USA include both animal feed systems with grain screenings and crop production systems including seed and equipment contamination. Regional awareness campaigns will be critical to support Canadian farmers in identifying and quickly mitigating invasions of Palmer amaranth and waterhemp to prevent establishment and spread of infestations into new areas.

Control of multiple herbicide-resistant waterhemp (Amaranthus tuberculatus) with acetochlor-based herbicide mixtures in corn

Abstract Waterhemp is a summer annual, broadleaf weed with high fecundity, short seed longevity in the soil, and wide genetic diversity. Populations have evolved resistance to five herbicide modes of action (Groups 2, 5, 9, 14, and 27), which are present across southern Ontario; this has increased the challenge of controlling this competitive weed species in corn, the most important grain crop produced worldwide, and the highest value agronomic crop in Ontario. Acetochlor is a Group 15 soil-applied residual herbicide that has activity on many grass and broadleaf weeds but has yet to be registered in Canada. The objective of this study was to ascertain whether mixtures of acetochlor with flumetsulam, dicamba, atrazine, isoxaflutole/diflufenican, or mesotrione + atrazine applied preemergence would increase the control of multiple herbicide-resistant (MHR) waterhemp in corn. Five field trials were conducted between 2022 and 2023. No corn injury was observed. Acetochlor applied alone controlled MHR waterhemp 97% 12 weeks after application (WAA). All herbicide mixtures controlled MHR waterhemp similarly at ≥98% 12 WAA; there were no differences among herbicide mixtures. Flumetsulam, dicamba, and atrazine provided lower MHR waterhemp control than all other herbicide treatments and did not reduce density or biomass. Acetochlor reduced waterhemp density 98%, while the acetochlor mixtures reduced density similarly at 99 to 100%. This study concludes that the acetochlor mixtures evaluated provide excellent waterhemp control; however, control was not greater than acetochlor alone. Herbicides herbicide mixtures should be used as a best management practice to mitigate the evolution of herbicide resistance.

Multiple resistance to EPSPS and ALS inhibitors in Palmer amaranth (Amaranthus palmeri) identified in Turkey

AbstractAmaranthus palmeri was first reported in Turkey in 2016, and an immediate heavy infestation of the weed was found in fruit orchards and summer crops such as maize, cotton, and sunflower. There have been farmers' complaints about the ineffective control of Palmer amaranth through the use of glyphosate and some sulfonylureas herbicides. Hence, this study aimed to determine the possible herbicide resistance evolution in Palmer amaranth against glyphosate and acetolactate synthase (ALS) herbicides. Seeds of 21 Palmer amaranth populations were collected from five provinces of Turkey where control problems with glyphosate and ALS inhibitors were reported in maize fields. Seeds of certain biotypes categorized as resistant or susceptible were grown to obtain the F2 generation. A single‐dose experiment determined the possible resistance to ALS inhibitors and glyphosate among the 21 populations. Of this, 18 populations were included in the subsequent dose–response experiments due to evident survival. Based on ED50 values from the dose–response experiment, SNU‐04 and ADN‐21 biotypes had the highest resistance index for glyphosate which was more than 7. The biotypes ADN‐21, OSM‐15, and DIR‐09 recorded the highest ED50 value with a resistance index of 9.21–10.35 after nicosulfuron application. Whereas, the biotypes SNU‐04, OSM‐15, and ADN‐21 were with the highest ED50 value and resistance index of 6.41–7.44, after the application of foramsulfuron + iodosulfuron methyl‐sodium. The increase in genomic 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS) copy number has been observed in suspected cases that have been accepted as the molecular basis for the development of resistance against glyphosate. The sequence alignment results for the ALS gene contained Ala122Val and Pro197Arg mutations related to target‐site resistance against ALS herbicides.

Verticillium Species as an Ecofriendly Alternative to Manage the Invasive Tree Ailanthus altissima (Mill.) Swingle

Environmental pollution, unintended harm to beneficial organisms, and the development of herbicide resistance among weeds are the main consequences of the massive and consistent use of chemical herbicides in recent decades. The growing need for alternative solutions has been reinforced by restrictive policies, leading to a search for natural herbicidal candidates. Mycoherbicides, formulations containing plant pathogenic fungi, are viewed as promising substitutes for chemical herbicides. In the case of Ailanthus altissima (Mill.) Swingle, one of the worst invasive alien tree species in the world, Verticillium-based mycoherbicides offer a viable method for control, inducing a lethal wilt disease and leading plants to death within a few years. The demonstrated significant effectiveness enables addressing challenges posed by other—conventional—approaches. The current analysis matches key internal (strengths and weaknesses) and external factors (opportunities and threats) of Verticillium Nees isolates as environmentally-friendly control agents against the invasive A. altissima, by listing each singularly and then crossing them among the categories, drawing from the collaborative efforts of American, Austrian, and Italian research teams.

Quantifying the impacts of management and herbicide resistance on regional plant population dynamics in the face of missing data

Abstract A key challenge in the management of populations is to quantify the impact of interventions in the face of environmental and phenotypic variability. However, accurate estimation of the effects of management and environment, in large‐scale ecological research is often limited by the expense of data collection, the inherent trade‐off between quality and quantity, and missing data. In this paper we develop a novel modelling framework, and demographically informed imputation scheme, to comprehensively account for the uncertainty generated by missing population, management, and herbicide resistance data. Using this framework and a large dataset (178 sites over 3 years) on the densities of a destructive arable weed (Alopecurus myosuroides) we investigate the effects of environment, management, and evolved herbicide resistance, on weed population dynamics. In this study we quantify the marginal effects of a suite of common management practices, including cropping, cultivation, and herbicide pressure, and evolved herbicide resistance, on weed population dynamics. Using this framework, we provide the first empirically backed demonstration that herbicide resistance is a key driver of population dynamics in arable weeds at regional scales. Whilst cultivation type had minimal impact on weed density, crop rotation, and earlier cultivation and drill dates consistently reduced infestation severity. Synthesis and applications: As we demonstrate that high herbicide resistance levels can produce extremely severe weed infestations, monitoring herbicide resistance is a priority for farmers across Western Europe. Furthermore, developing non‐chemical control methods is essential to control current weed populations, and prevent further resistance evolution. We recommend that planning interventions that centre on crop rotation and incorporate spring sewing and cultivation to provide the best reductions in weed densities. More generally, by directly accounting for missing data our framework permits the analysis of management practices with data that would otherwise be severely compromised.

The Pro-197-Thr mutation in the ALS gene confers novel resistance patterns to ALS-inhibiting herbicides in Bromus japonicus in China.

Bromus japonicus is one of the most notorious agricultural weeds in China. The long-term use of ALS-inhibiting herbicides has led to rapid evolution of herbicide resistance in B. japonicus. B. japonicus population (BJ-R) surviving mesosulfuron-methyl treatment was collected from wheatland. Here, we aimed to confirm the resistance mechanisms in this putative resistant population. The dose-reponse tests were used to test the resistance level of the B. japonicus to ALS-inhibiting herbicides. Pretreatment with P450 and GST inhibitors and GST activity assays were used to determine whether P450 or GST was involved in the resistance of the BJ-R population. Sanger sequencing was used to analyse the ALS mutation of the BJ-R population. RT-qPCR was used to confirm the the expression levels of the ALS gene in mesosulfuron-methyl -resistant (BJ-R) and-susceptible (BJ-S) B. japonicus. An in vitro ALS activity assay was used to determine the ALS activity of the BJ-R and BJ-S populations. Homology modelling and docking were used to determine the binding energy of the BJ-R and BJ-S populations with ALS-inhibiting herbicides. B. japonicus population (BJ-R) was confirmed to be 454- and 2.7-fold resistant to the SU herbicides mesosulfuron-methyl and nicosulfuron, and 7.3-, 2.3-, 1.1- and 10.8-fold resistant to the IMI herbicide imazamox, the TP herbicide penoxsulam, the PTB herbicide pyribenzoxim and the SCT herbicide flucarbazone-sodium, respectively, compared with its susceptible counterpart (BJ-S). Neither a P450 inhibitor nor a GST inhibitor could reverse the level of resistance to mesosulfuron-methyl in BJ-R. In addition, no significant differences in GST activity were found between the BJ-R and BJ-S. ALS gene sequencing revealed a Pro-197-Thr mutation in BJ-R, and the gene expression had no significant differences between the BJ-R and BJ-S. The ALS activity of BJ-R was 106-fold more tolerant to mesosulfuron-methyl than that of BJ-S. Molecular docking showed that the binding energy of the ALS active site and mesosulfuron-methyl was changed from -6.67 to -4.57 kcal mol-1 due to the mutation at position 197. These results suggested that the Pro-197-Thr mutation was the main reason for the high resistance level of BJ-R to mesosulfuron-methyl. Unlike previous reports of the cross-resistance pattern conferred by this mutation, we firstly documented that the Pro-197-Thr mutation confers broad cross-resistance spectrums to ALS-inhibiting herbicides in B. japonicus.

Joint Action of Selective Herbicides used in Paddy Field on Control of Lemna minor L.

To minimise herbicide inputs, reduce environmental burdens, and delay the evolution of herbicide resistance, it is of the utmost significance to study the interaction between herbicides. This may be accomplished by selecting the optimal combination, which, through synergy, delivers more cost-effective weed control than a single herbicide. Under laboratory conditions, interactions between binary mixtures of bensulfuron, propanil, 2,4-D, or bentazon on chlorophyll reduction of Lemna minor were investigated using the Additive Dose Model. Mixtures of propanil/2,4-D resulted in low antagonism whereas strong antagonism was evident in bensulfuron-methyl/propanil. Combinations of bensulfuron/bentazon and bensulfuron/2,4-D led to moderate antagonism. By contrast, propanil in combination with bentazon demonstrated a modest degree of synergism. The findings of this study could provide good guideline and insights when mixing two herbicides for weed control in rice fields and other aquatic environment.

Herbicide‐resistant weeds from dryland agriculture in Argentina

AbstractWe reviewed and performed a quantitative synthesis on herbicide‐resistant weeds from rain‐fed crops in Argentina. Twenty‐four weed species distributed in the main extensive crops (soybean, maize, wheat, barley, oilseed rape, sunflower, chickpea and peanut) have evolved herbicide resistance. Of the total, 54% are grasses, 88% are annual species and 63% are cross‐pollinated species. The most representative families were Poaceae with 54% resistant species, followed by Brassicaceae with 17%, and Asteraceae with 13%. Buenos Aires, Santa Fe and Córdoba were the provinces with the most documented cases of resistance (35%, 33% and 30%, respectively). The proportion of cases resistant to pre‐emergence herbicides was 10%, whereas the proportion of cases resistant to post‐emergence herbicides was 90%. Glyphosate was the herbicide with the highest incidence (92%) of resistance among weed species, followed by 29% of species that evolved resistance to ALS‐inhibiting herbicides. Whereas resistance to auxin‐like herbicides comprised 17% of the weed species, acetyl‐CoA carboxylase (8%) and protoporphyrinogen oxidase (4%) inhibiting herbicides showed the least incidence of resistance evolution among weeds. The highest number of resistant species was identified in soybean (19), followed by maize (13), wheat/barley (10) and fallow (9). Weed species with a higher number of resistant populations to a higher number of herbicide mode of action were Amaranthus hybridus, A. palmeri, Lolium multiflorum and Raphanus sativus. The change in the production system since the mid‐1990s, based on the use of herbicides (glyphosate mainly) to control weeds, is likely to account for the notorious increase in the average rate of evolution of herbicide‐resistant weeds in Argentina.

Novel use pattern of pendimethalin for annual ryegrass (Lolium rigidum Gaudin) control in wheat and barley

Annual ryegrass (Lolium rigidum Gaudin) is a problematic weed in most of the cropping regions in Australia. Evolved herbicide resistance to multiple modes of action groups, the lack of new herbicidal molecules, and the emergence of late cohorts in winter season crops necessitate the use of existing herbicides in an innovative way to control L. rigidum. Pendimethalin as pre-emergence (PRE) is used for L. rigidum control; however, it is unable to control late cohorts of L. rigidum in winter season crops. Pot studies were conducted from 2019 to 2021 to evaluate the effect of a post-emergence (POST) application of pendimethalin with six doses (0, 220, 440, 880, 1,760, and 3,520 g a.i. ha-1) on L. rigidum control in addition to crop safety in wheat, barley, and sorghum. POST application of pendimethalin was found to be safe for wheat and barley, and the biomass reduction in both crops at varied rates (220 to 3,520 g ha−1) of pendimethalin ranged from 10% to 20%. A dose–response study revealed that the pendimethalin dose required for 50% mortality and growth reduction of L. rigidum was 179 and 144 g ai ha−1, respectively. Pendimethalin at 880 g ai ha−1 completely killed late cohorts of L. rigidum. These results suggest that the POST application of pendimethalin can be used for the effective control of late cohorts of L. rigidum in wheat and barley crops. POST application of pendimethalin suppressed the biomass of sorghum plants compared with the non-treated control treatment, and biomass reduction in sorghum at different pendimethalin doses ranged from 32% to 40%. Results implied that POST applications of pendimethalin in wheat and barley can diversify herbicide programs in managing L. rigidum and may help in delaying the evolution of resistance in this weed.

Management of Herbicide-Resistant Common Lambsquarters, Chenopodium album , in Atlantic Canada

Abstract Common lambsquarters ( Chenopodium album ) is one of the most troublesome annual broadleaf weeds in potato production in Atlantic Canada. Historically controlled by a combination of cultivation and herbicides, potato producers now often rely on a single herbicide application to provide season long control of common lambsquarters. The reliance on a few herbicides for common lambsquarters control has led to widespread incidence of herbicide resistance in this species, negatively impacting potato yield. This case study explores common lambsquarters’ biology, development of herbicide resistance, and the evolving management practices including chemical, cultural, and mechanical to help mitigate its impact on potato productivity. Information © The Author 2024

Non–target site mechanisms of cross-resistance evolution to florpyrauxifen-benzyl in 2,4-D–resistant Palmer amaranth (Amaranthus palmeri)

AbstractThe evolution of herbicide resistance in weeds can reduce the herbicide’s efficacy, depleting crop yield and quality. Our group previously confirmed 2,4-D resistance in three Palmer amaranth (Amaranthus palmeri S. Watson) populations (R1 to R3). In the current study, the first filial (F1) seeds of 2,4-D–resistant populations were subjected to screening tests for resistance to other auxin-mimicking herbicides, florpyrauxifen-benzyl (FPB; 30 g ai ha−1) and dicamba (560 g ae ha−1). Dicamba killed all resistant populations. FPB provided 100% control of only the R3 population. Sensitivities to FPB were reduced by 2 and 35 percentage points in R1 and R2 populations, respectively. Pretreatment with malathion increased FPB sensitivity by 15 percentage points in the R2 population. FPB resistance characterization and mechanism were evaluated using a purified line of the R2 population (F2). The FPB sensitivity was 29-fold lower in the F2 line than in the susceptible (S) standard. Absorption, translocation, and total metabolism of FPB were similar for S and R2 populations. However, less florpyrauxifen-acid (FPA) was detected in the R2 population (17.0% to 25.4%) than in the S population (22.8% to 33.2%), due to its rapid metabolism and/or reduced production with resistance evolution. Because the results of the non–target site resistance mechanism evaluation observed in this study were insufficient to account for the 29-fold reduced sensitivity of the R2 population to FPB, further genetic studies are needed to investigate the presence of target-site resistance in that population.

Integrated Weed Management in Minor Millets: A Review

Presently, agriculture is facing tremendous problem due to climate change and global warming. To ensure food and nutritional security at national level, there is an immediate need to promote the cultivation of millets as millets are considered climate smart and nature friendly crops because of high nutritive value and can withstand under warm and drought conditions with short life, low external inputs requirement, tolerance to water and temperatures stress. Ten millet crops have been declared as ‘Nutri Cereals’ which include three major millets i.e., pearl millet, sorghum and finger millet; five minor millets i.e. foxtail millet, proso millet, kodo millet, barnyard millet, little millet; and two pseudo millets i.e. kuttu (buckwheat) and amaranthus. Due to sluggish growth in initial phases of life, millets proved relatively poor competitors against weeds. Manual weeding is the most commonly adopted for weed control in millets. But the non-availability of labour and ever-increasing labour wages have compelled the farmers to seek alternate method of weed management. Herbicide use is the most viable method of weed control but their continuous and excessive use is not advisable due to its ill effects on environment and development of herbicide resistance in weeds. Very limited options are available in literature for weed control in minor millets. Thus, integrated weed management practices should be followed on site and time specific basis for effective and efficient weed management in minor millets. For integrated weed management in minor millets, 2-3 times inter-cultivation and 1-2 time hand weeding during initial 25 days after sowing in addition to pre-emergence spray with Isoproturon @ 0.5 -1.0 kg a.i./ha and post emergence spray of 2, 4-D sodium salt @ 0.75-1.0 kg a.i./ha at 20-25 days after sowing should be done for effective weed control.

Repeated evolution of herbicide resistance in Lolium multiflorum revealed by haplotype-resolved analysis of acetyl-CoA carboxylase.

Herbicide resistance in weeds is one of the greatest challenges in modern food production. The grass species Lolium multiflorum is an excellent model species to investigate evolution under similar selection pressure because populations have repeatedly evolved resistance to many herbicides, utilizing a multitude of mechanisms to neutralize herbicide damage. In this work, we investigated the gene that encodes acetyl-CoA carboxylase (ACCase), the target site of the most successful herbicide group available for grass weed control. We sampled L. multiflorum populations from agricultural fields with history of intense herbicide use, and studied their response to three ACCase-inhibiting herbicides. To elucidate the mechanisms of herbicide resistance and the genetic relationship among populations, we resolved the haplotypes of 97 resistant and susceptible individuals by sequencing ACCase amplicons using long-read DNA sequencing technologies. Our dose-response data indicated the existence of many, often unpredictable, resistance patterns to ACCase-inhibiting herbicides, where populations exhibited as much as 37-fold reduction in herbicide response. The majority of the populations exhibited resistance to all three herbicides studied. Phylogenetic and molecular genetic analyses revealed multiple evolutionary origins of resistance-endowing ACCase haplotypes, as well as widespread admixture in the region regardless of cropping system. The amplicons generated were diverse, with haplotypes exhibiting 26-110 polymorphisms. Polymorphisms included insertions and deletions 1-31 bp in length, none of which were associated with the resistance phenotype based on an association analysis. We also found evidence that some populations have multiple mechanisms of resistance. Our results highlight the astounding genetic diversity in L. multiflorum populations, and the potential for repeated evolution of herbicide resistance across the landscape that challenges weed management approaches and jeopardizes sustainable weed control practices. We provide an in-depth discussion of the evolutionary and practical implications of our results.

Ethofumesate-resistant annual bluegrass (Poa annua) in grass seed production systems

AbstractThe prolific seed production and polyploidy of annual bluegrass allow for the rapid development of herbicide resistance. Ethofumesate-resistant annual bluegrass plants were identified in the 1990s in grass seed production in Oregon, but their prevalence and distribution are not well documented. Therefore a dose–response experiment was initiated to determine the potential level of ethofumesate resistance in seed production systems. Seeds from 55 annual bluegrass populations were obtained from three sources: seed production fields (31 populations), the seed cleaning process (6 populations), and seed testing lots prior to retail distribution (18 populations). Additionally, two populations, one with known ethofumesate resistance and one with known susceptibility, were identified in preliminary testing and used as controls in this experiment. Seed from each collected population was increased. Individual seedlings were then transplanted into separate cone-tainers, grown to a size of 2 to 3 tillers in the greenhouse, and then sprayed using a compressed air track spray chamber with 10 doses of ethofumesate at 0, 0.56, 1.1, 2.8, 5.6, 8.4, 11.2, 16.8, 22.4, and 44.8 kg ai ha−1, with 0.84 to 2.2 kg ha−1 as the label application rate for perennial ryegrass. The resistant to susceptible ratio of populations across all sources ranged from 0.5 to 5.5. The most resistant populations found in production fields, seed cleaning, and seed testing lots had the effective dose necessary to kill 50% of the population (ED50) of 12.1, 9.4, and 13.1 kg ha−1, respectively. Furthermore, 68% of the populations found in production fields had ED50 higher than 6 kg ha−1, indicating common annual bluegrass resistance in grass seed production. As such, growers should implement integrated weed management strategies, as herbicides alone will likely be ineffective at controlling annual bluegrass.

Comprehensive insights into herbicide resistance mechanisms in weeds: a synergistic integration of transcriptomic and metabolomic analyses.

Omics techniques, including genomics, transcriptomics, proteomics, and metabolomics have smoothed the researcher's ability to generate hypotheses and discover various agronomically relevant functions and mechanisms, as well as their implications and associations. With a significant increase in the number of cases with resistance to multiple herbicide modes of action, studies on herbicide resistance are currently one of the predominant areas of research within the field of weed science. High-throughput technologies have already started revolutionizing the current molecular weed biology studies. The evolution of herbicide resistance in weeds (particularly via non-target site resistance mechanism) is a perfect example of a complex, multi-pathway integration-induced response. To date, functional genomics, including transcriptomic and metabolomic studies have been used separately in herbicide resistance research, however there is a substantial lack of integrated approach. Hence, despite the ability of omics technologies to provide significant insights into the molecular functioning of weeds, using a single omics can sometimes be misleading. This mini-review will aim to discuss the current progress of transcriptome-based and metabolome-based approaches in herbicide resistance research, along with their systematic integration.

Responses of rice genotypes to foliar-applied metribuzin

AbstractThe increasing development of herbicide resistance in weeds found in rice cropping systems has encouraged researchers to evaluate alternate herbicides to prevent and manage herbicide-resistant weed biotypes. Metribuzin is a photosynthetic-inhibiting herbicide that controls various important grass and broadleaf weeds. Several crops, including soybean, wheat, peas, and potato, have shown differential varietal responses to metribuzin. To determine whether rice has differential varietal responses to metribuzin for potential utilization in a rice breeding program, greenhouse experiments were conducted to evaluate the responses of 142 long-, medium-, and short-grain rice genotypes to the herbicide. Metribuzin was applied at 0, 22, 44, 88, 176, and 352 g ai ha−1 when rice plants were in the 3- to 4-leaf stage. Crop response regarding phytotoxicity, height reduction, and biomass reduction was evaluated. Metribuzin caused significant injury to all rice genotypes tested, but short-grain rice genotypes were, on average, more susceptible than medium- and long-grain rice genotypes. Short-grain rice genotypes generally had greater height reduction and produced less biomass than long-grain or medium-grain rice genotypes. Crop visual injury ratings were correlated with plant height reductions and biomass reductions. The results indicate that the level of metribuzin tolerance in rice is inadequate for commercial use; however, further research is needed to develop higher levels of herbicide resistance by mutagenized rice cultivars.

Strengths and Weaknesses of Non-chemical Weed Management Strategies in Small-scale Vegetable Production

Weeds are continuing to create problems for vegetable growers more than ever before due to climate change, frequent cultivation, and the evolution of herbicide resistance. Weeds not only decrease vegetable yields but also reduce their quality. This case study aims to investigate weed management strategies, their strengths and weaknesses, and, the scope for improvements in a small-scale vegetable garden in Australia. The Armidale community garden in the New England region was selected for this study because of its wider types of vegetable production. The data was collected by observing and, taking an in-depth and unstructured interview of the convener of the garden. The study showed that the growers only use non-chemical weed management strategies to tackle the predicament. Mechanical and cultural methods including mulching, hand weeding, tillage, and grazing are mainly used to manage the weed infestation in the vegetable garden. Among them mulching with wood chips and hand weeding were considered more effective in minimizing the weed competition during the critical periods of crop development but they could not reach a satisfactory level. Thus, further improvements by integrating several approaches simultaneously are needed to control weeds more effectively and economically. The outcomes of the study will benefit both conventional and organic vegetable producers as well as researchers to keep weed populations at a manageable level.

Variability to flooding tolerance in barnyardgrass and early flooding benefits on weed management and rice grain yield

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) is one of the most problematic weed species in paddy fields. The recent large-scale evolution of herbicide resistance in this species requires the adoption of integrated methods of weed control. The present study aimed to determine the interaction of water depth, flooding irrigation onset, and pre-emergent herbicides on the control of barnyardgrass populations and to identify the variability and the putative genes involved in the regulation of flooding tolerance in this species. We identified tolerant, moderately tolerant, and flood-sensitive barnyardgrass populations through water depth-response experiments in a greenhouse. The relative expression of genes related to flooding tolerance were evaluated to confirm the flooding tolerance variability. A field experiment was conducted during the summer seasons of 2020/21 and 2021/22 to assess the interaction of the flooding onset, water depth, and pre-emergent herbicides on populations with different flood tolerances and herbicide resistance mechanisms. Water depths of 7.5 cm and 12.5 cm and plant height were selected for the diagnosis of flood tolerance. After 28 days under flooding, the 7.5 cm depth reduced plant height by an average of 26.82%. Of the 45 populations evaluated, 43 overcame the water depth of 7.5 cm, and four surpassed 12.5 cm. The relative expression of alcohol dehydrogenase 1 (ADH1), alcohol dehydrogenase 2 (ADH2), pyruvate decarboxylase (PDC1), aldehyde dehydrogenase (ALDH), and sucrose synthase 3 (SUS3) was between eight and sixteen times higher for the flood-tolerant population than for the sensitive one. In the field study, the anticipation of flooding to the two-leaves (V2) stage of rice resulted in an increase of up to 55.6% in the control of all populations evaluated compared with conventional irrigation at the four-leaves (V4) stage, including those resistant to herbicides. The grain yield was increased by approximately 11.4% with flooding onset in the V2 stage compared to the V4 stage. Barnyardgrass control and rice grain yield were not affected by water depths of 5 cm or 15 cm. The early flooding, in the V2 stage, increased rice grain yield and favored barnyardgrass control. However, variability in flood tolerance was identified in barnyardgrass populations, which may jeopardize the effect of early flooding for weed control in rice crops. The results we obtained add information on the basic knowledge of flooding tolerance in barnyardgrass and to the integrated weed management for dry direct-seeded rice.