Resistant Weeds Research Articles

Near‐term challenges for global agriculture: Herbicide‐resistant weeds

AbstractPrior to the 1950s, weeds were controlled by a wide variety of mechanical and cultural methods with limited use of inorganic chemicals at very high rates (100s kg ha–1). With the advent of selective carbon‐based herbicides in the 1950s, herbicide weed management became the norm throughout much of the world, using grams to a few kilograms of active ingredient per hectare. However, with the benefits, there are problems. A few resistant weeds were recognized in the 1970s, but in 2021, 521 unique cases of resistance have been documented throughout the world. It is imperative for farmers to rethink the herbicide paradigm and for researchers to explore and provide alternative weed management methods so that today's herbicides maintain efficacy and benefits into the future. Near‐term management strategies include going back to more integrated approaches, using mechanical techniques, and linking to new technologies to hit weeds with “many little hammers” rather than the “sledge hammer” of one or multiple herbicides.

Effect of Method of Application, Herbicide Rate and Cultivar on Processing Pea Tolerance to Saflufenacil

The purpose of this work was to determine the effect of method of application, herbicide rate and cultivar on tolerance of processing pea tolerance to saflufenacil. Two field experiments were established to address this—each experiment was conducted over a 3-year period. The first experiment, conducted in 2014, 2015 and 2016, was arranged in a split-plot design with method of application (pre-plant incorporation (PPI) or preemergence (PRE)) as the main plot factor, and saflufenacil rate (0, 75 and 150 g ai ha-1) as the subplot factor. Pea (Pisum sativum L.) was not injured, and dry matter, pea tenderness and yield were not less than the untreated check when saflufenacil was applied either PPI or PRE, at 75 and 150 g ai ha-1 of the herbicide. The second experiment was conducted from 2017 to 2019, at two locations each year; each repetition of this experiment was arranged in a factorial design to determine the effect of two factors on processing pea: saflufenacil rate (0, 75 and 150 g ai ha-1) and cultivar. Saflufenacil did not cause more than 5% visible injury to pea, nor did it reduce pea dry matter, tenderness or marketable yield of the eight cultivars included in the experiment. Application method, saflufenacil rate and cultivar did not affect pea tolerance across a wide range of soil and environmental conditions. Registration of saflufenacil in processing pea would significantly improve growers’ options for control of Group 2 resistant broadleaf weeds such as common lamb’s-quarters (Chenopodium album L.), eastern black nightshade (Solanum ptycanthum Dunal.) and common ragweed (Ambrosia artemisiifolia L.).

Systematic, small-scale screening with Arabidopsis reveals herbicides synergies that extend to lettuce.

Combining herbicides into a mixture is a common approach used to overcome the potential for herbicide resistance in weeds. Many herbicide mixtures can be antagonistic and they are rarely synergistic. Here, 24 commercial herbicides, each representing a different mode of action were used to create a matrix of all 276 unique combinations to search for new synergies in agar using Arabidopsis thaliana. Herbicides were used at an appropriate sublethal dose such that any synergies gave visible growth inhibition. We found five synergies including three new ones, namely mesotrione-norflurazon, mesotrione-clethodim and clomazone-paraquat. All three were reproducible in soil-grown conditions. Interestingly, the three new combinations all included a bleaching herbicide, suggesting that synergy might be a class-specific phenomenon. We also found that mesotrione-norflurazon and mesotrione-clethodim combinations were also synergistic against lettuce (Lactuca sativa), but not tef (Eragrostis tef). Our study shows that screening herbicide mixtures against A. thaliana is an efficient approach for finding rare herbicide synergies.

Glyphosate Herbicide: Reproductive Outcomes and Multigenerational Effects.

Glyphosate base herbicides (GBHs) are the most widely applied pesticides in the world and are mainly used in association with GBH-tolerant crop varieties. Indiscriminate and negligent use of GBHs has promoted the emergence of glyphosate resistant weeds, and consequently the rise in the use of these herbicides. Glyphosate, the active ingredient of all GBHs, is combined with other chemicals known as co-formulants that enhance the herbicide action. Nowadays, the safety of glyphosate and its formulations remain to be a controversial issue, as evidence is not conclusive whether the adverse effects are caused by GBH or glyphosate, and little is known about the contribution of co-formulants to the toxicity of herbicides. Currently, alarmingly increased levels of glyphosate have been detected in different environmental matrixes and in foodstuff, becoming an issue of social concern. Some in vitro and in vivo studies have shown that glyphosate and its formulations exhibit estrogen-like properties, and growing evidence has indicated they may disrupt normal endocrine function, with adverse consequences for reproductive health. Moreover, multigenerational effects have been reported and epigenetic mechanisms have been proved to be involved in the alterations induced by the herbicide. In this review, we provide an overview of: i) the routes and levels of human exposure to GBHs, ii) the potential estrogenic effects of glyphosate and GBHs in cell culture and animal models, iii) their long-term effects on female fertility and mechanisms of action, and iv) the consequences on health of successive generations.

Characterization of mutations conferring inherent resistance to acetyl coenzyme A carboxylase‐inhibiting herbicides in turfgrass and grassy weeds

AbstractAn herbicide‐resistant weed control system that utilizes naturally occurring mutations to acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides could provide herbicide selectivity and improve control of grassy weeds in turf. Knowledge regarding the presence of these mutations in grasses is needed to guide development of this type of system. This research subjected 24 species of warm‐season, cool‐season, and grassy weed species to rates of 0, 400, and 1200 g a.i. ha−1 of fenoxaprop herbicide and surveyed these species for the presence of site‐of‐action mutations in ACCase at amino acid (aa) positions 1781, 1999, 2027, 2041, 2076, 2088, and 2096. Nine species including Agrostis capillaris L., Festuca ovina L., Festuca rubra L., Lolium multiflorum Lam., Lolium perenne L., Paspalum dilatatum Poir., Poa annua L., Zoysia japonica Steud., and Z. matrella [L.] Merr. were tolerant to fenoxaprop. Site of action point mutations conferring resistance to ACCase herbicides were found at aa position 1781 in only three of 24 species surveyed (Festuca ovina, Festuca rubra, and Poa annua). The information obtained from this study provide guidance for the development of ACCase resistant weed control systems for turfgrass.

A, The Evaluating Allelopathic potential of aqueous extracts of Sow thistle (Sonchus oleraceus L.) on emergence and seedling growth of Red rice (Oryza punctata)

ABSTRACT Chemical weed control method caused environmental hazards and residual effects in crops and soil. Alternate approach to control weeds is getting attentions in sustainable production system. Use of aqueous extracts of weed is getting scientific attention as eco-friendly alternative to chemical herbicides especially under scenario of fast increasing herbicide resistance in weeds. To investigate the herbicidal potential of aqueous extract of winter weed of Sonchus oleraceus L. (Sow thistle) on summer weed Oryza punctate L. (red rice) seed emergence and initial seedling growth, a study was planned. In this study, seeds of O. punctate were incubated in seven concentrations (0, 0.25, 0.50, 1, 2, 4, and 8%) of different parts i.e. leaves, stem, flower of S. oleraceus. All the tested concentrations of various plant parts of S. oleraceus significantly inhibited the mean emergence time, emergence index, emergence percentage (%), time taken to 50% emergence as well as growth of O. punctata weed. However, maximum mean emergence time (5.26 days), minimum germination index (1.69), germination percentage (40%), root length (2.04 cm), shoot length (5.71 cm), fresh weight (59 g), dry weight (4.06 g) was noted at 8% concentration with fruit aqueous extract of S. oleraceus. Seed of O. punctata take maximum time to complete 50% emergence (3.33 days) under control where we applied distilled water. Results suggested fruit extract of S. oleraceus at 8% concentration can be used potential bio-herbicide for the control of O. punctate. Key words: Chemical, eco-friendly, herbicidal potential, fruit extract

Transcriptomic analysis reveals the transcription factors involved in regulating the expression of EPSPS gene, which confers glyphosate resistance of goosegrass (Eleusine indica)

Glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and overexpression of the EPSPS gene is one of the molecular mechanisms conferring glyphosate resistance in weeds. A regulatory sequence of EPSPS gene was isolated previously, and an alteration in its 5´-untranslated region (UTR) pyrimidine (Py)-rich stretch element is involved in the regulation of EPSPS expression in glyphosate-resistant (GR) Eleusine indica. However, the transcription factors involved in this regulatory sequence remain to be elucidated. In this study, we investigated the regulatory network of EPSPS overexpression associated genes in a GR E. indica population by RNA-seq. The differentially expressed transcript analyses revealed that glyphosate treatment caused an increase in the expression of 2752 unigenes and a decrease in the expression of 4025 unigenes in the GR E. indica, compared to the glyphosate-susceptible (GS) E. indica. Among them, 1373 unigenes were identified to be co-expressed with the EPSPS gene in GR E. indica. GO and KEGG pathway analyses showed that the up-regulated unigenes were mainly enriched in chloroplasts and associated with the shikimate biosynthesis pathway, chlorophy II and peroxisome metabolism processes. Notably, the expression of a Shikimate kinase which catalyzed the conversion of Shikimate to Shikimate 3-phosphate (S3P, a substrate of EPSPS), was also up-regulated. Eight transcription factors were identified as likely to be involved in the regulation of the EPSPS expression, and three of them (ARF2, ARF8 and BPC6) showed more binding sites because of a (CT)n insertion of the 5´-UTR Py-rich stretch element in GR. However, the yeast one-hybrid assay illustrated that ARF8 and BPC6 could bind to the 5´-UTR Py-rich stretch element of wild type EPSPS, but could not bind to the mutated form. Our data suggests that the transcriptional regulation of EPSPS expression is complex and was significantly altered in GR E. indica. These discoveries provide new references for further study of the EPSPS overexpression mechanism that endows glyphosate resistance.

Recurrent Selection with Sub-Lethal Doses of Mesotrione Reduces Sensitivity in Amaranthus palmeri.

Amaranthus palmeri, ranked as the most prolific and troublesome weed in North America, has evolved resistance to several herbicide sites of action. Repeated use of any one herbicide, especially at lower than recommended doses, can lead to evolution of weed resistance, and, therefore, a better understanding of the process of resistance evolution is essential for the management of A. palmeri and other difficult-to-control weed species. Amaranthus palmeri rapidly developed resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors such as mesotrione. The objective of this study was to test the potential for low-dose applications of mesotrione to select for reduced susceptibility over multiple generations in an A. palmeri population collected from an agricultural field in 2001. F0 plants from the population were initially treated with sub-lethal mesotrione rates and evaluated for survival three weeks after treatment. All F0 plants were controlled at the 1× rate (x = 105 g ai ha−1). However, 2.5% of the F0 plants survived the 0.5× treatment. The recurrent selection process using plants surviving various mesotrione rates was continued until the F4 generation was reached. Based on the GR50 values, the sensitivity index was determined to be 1.7 for the F4 generation. Compared to F0, HPPD gene expression level in the F3 population increased. Results indicate that after several rounds of recurrent selection, the successive generations of A. palmeri became less responsive to mesotrione, which may explain the reduced sensitivity of this weed to HPPD-inhibiting herbicides. The results have significance in light of the recently released soybean and soon to be released cotton varieties with resistance to HPPD inhibitors.

Herbicide Resistance to Metsulfuron-Methyl in Rumex dentatus L. in North-West India and Its Management Perspectives for Sustainable Wheat Production

Herbicide resistance in weeds is a global threat to sustaining food security. In India, herbicide-resistant Phalaris minor was the major problem in wheat for more than two decades, but the continuous use of metsulfuron-methyl (an ALS inhibitor) to control broadleaf weeds has resulted in the evolution of ALS inhibitor-resistant Rumex dentatus L. This review summarizes the current scenario of herbicide resistance in R. dentatus, along with its ecology and management perspectives. Studies have provided valuable insights on the emergence pattern of R. dentatus under different environments in relation to tillage, cropping systems, nutrients, and irrigation. Moreover, R. dentatus has exhibited higher emergence under zero tillage, with high infestation levels in rice-wheat compared to other wheat-based cropping systems (sorghum-wheat). Alternative herbicides for the management of resistant R. dentatus include pendimethalin, 2,4-D, carfentrazone, isoproturon, and metribuzin. Although the pre-emergence application of pendimethalin is highly successful in suppressing R. dentatus, but its efficiency is questionable under lower field soil moisture and heavy residue load conditions. Nevertheless, the biological data may be utilized to control R. dentatus. Therefore, herbicide rotation with suitable spray techniques, collecting weed seeds at differential heights from wheat, crop rotation, alternate tillage practices, and straw retention are recommended for addressing the resistance issue in R. dentatus in North India conditions. Overall, we discuss the current state of herbicide resistance in R. dentatus, the agronomic factors affecting its population, its proliferation in specific cropping systems (rice-wheat), and management strategies for containing an infestation of a resistant population.

The Use of Intellectual Property Systems in Plant Breeding for Ensuring Deployment of Good Agricultural Practices

Breeding innovations are relevant for sustainable agricultural development and food security, as new, resilient production systems require crop varieties optimally suited for these systems. In the societal debate around genetic engineering and other plant breeding innovations, ownership of patents on the technology used in the hands of large companies is often seen as a reason that small breeding companies are denied opportunities for further improving varieties or that farmers are restricted in using such varieties. However, intellectual property (IP) systems may also be used as tools to ensure the use of good agricultural practices when cultivating the resulting varieties. This paper explores documented cases in which IP systems (plant variety rights, patents and brand names) are used to promote that innovative varieties are grown according to good agricultural practices (GAP). These include effective disease resistance management regimes in innovative crop varieties of potato in order to prevent or delay pathogens from overcoming disease resistance genes, management regimes for transgenic insect-resistant Bt or herbicide-tolerant crops to prevent the development of resistant pests or weeds, respectively. The results are discussed with respect to the influence of breeders on GAP measures through various forms of IP and the contribution and role of other stakeholders, authorities and society at large in stimulating and ensuring the use of GAP.

Comprehensive machine learning based study of the chemical space of herbicides

Widespread use of herbicides results in the global increase in weed resistance. The rotational use of herbicides according to their modes of action (MoAs) and discovery of novel phytotoxic molecules are the two strategies used against the weed resistance. Herein, Random Forest modeling was used to build predictive models and establish comprehensive characterization of structure–activity relationships underlying herbicide classifications according to their MoAs and weed selectivity. By combining the predictive models with herbicide-likeness rules defined by selected molecular features (numbers of H-bond acceptors and donors, logP, topological and relative polar surface area, and net charge), the virtual stepwise screening platform is proposed for characterization of small weight molecules for their phytotoxic properties. The screening cascade was applied on the data set of phytotoxic natural products. The obtained results may be valuable for refinement of herbicide rotational program as well as for discovery of novel herbicides primarily among natural products as a source for molecules of novel structures and novel modes of action and translocation profiles as compared with the synthetic compounds.

Herbicide resistant weeds: the case of resistance to glyphosate

Glyphosate has become the most widely used herbicide worldwide since 1974 with a global use of 8.6 billion kg (glyphosate active ingredient) between 1974 and 2014. This study reports on glyphosate resistant (GR) weeds and their resistance mechanisms based on global scientifically reported cases. Forty-nine different weed species have evolved resistance to glyphosate in 29 countries with a total of 318 identified cases worldwide. Fifty percent of these resistance cases were found in glyphosate-resistant cropping systems. There were 255 identified cases (80.2%) of glyphosate resistance in the top five countries (in terms of number of cases and species), namely USA, Australia, Argentina, Brazil, and Canada. The five most popular weed species (in terms of number of cases) found to be resistant to glyphosate were Conyza canadensis, Amaranthus palmeri, Amaranthus tuberculatus, Lolium perenne ssp. Multiflorum,and Ambrosia artemisiifolia with 42, 42, 29, 26, and 21 reported cases, respectively. Out of 49 weed species, 19 GR weed species were found to not only be resistant to glyphosate but also to other herbicide sites of action (multiple herbicide resistance). Glyphosate resistance mechanisms in weeds include (1) target-site alterations: target-site mutation and target-site gene amplification; and (2) non-target-site mechanisms involving different modes of exclusion from the target site: reduced glyphosate uptake, reduced glyphosate translocation, and enhanced glyphosate metabolism. It is essential to have an integrated weed management program that includes not only smart herbicide mixtures and rotations, but also cultural, manual, mechanical, and crop-based weed management methods.

A REVIEW ON WEED IN DIRECT-SEEDED RICE (DSR)

Oryza sativa, cereal crop grown worldwide which feeds 60% of world. DSR, feasible and resource conserving technique of rice cultivation is gaining popularity, but due to weed infestation, crop experience a yield loss from 15%-100%. Various journals were assessed and books were consulted with the objective of compiling the various weeds of DSR and their management strategies in a comprehensive single document. Weed can be manage by different methods but integration of all methods is the best and eco-friendly compared to chemical one. Biotechnological method for development of herbicide resistance varieties, biological methods are new and are best alternative options. Different pre and post emergence herbicides could be applied to kill or suppress in short period with recommended doses and stage of crop. No single method is perfect for killing all the weeds, integrating different strategies having different modes of action can reduce the weed density and resistance to herbicides.

USDA Research

It had been a long time since the author last participated in a series of presentations on Integrated Weed Management (IWM) and he left it with mixed feelings. The first presentation from Henry Creissen, only 65% of the 225 responses to his IPM survey claimed to be practising IPM and it seemed to me that there was some way to go to encourage its take up and the need for inclusion of IPM in legislation was understandable. However, in most of the following presentations, IWM was clearly being practiced. As Sean Sparling stated, most farmers practice it whether they know it or not and that it is common sense. I would like to think that most, if not all farmers and growers, practice IWM measures and practice sustainable agricultural and horticultural practices. Hopefully, the days of unsustainable mono-cultural practices with repeated use of the same herbicides for weed control, year after year, have passed, as many of these herbicides now have resistance issues, even if they are still available. Changing weather conditions will mean adjusting weed management practices, which if sustainable will meet IWM requirements. One concern is that all presenters stated that herbicides were a key component of IWM, particularly the use of glyphosate. Its use is threatened from a regulatory perspective, or more appropriately political perspective, although regulatory science does not suggest there is an issue. However there is also the issue of loss of efficacy due to the development of weed resistance due to overuse. I live in hope that glyphosate can remain as part of the toolbox IWM and that my former colleagues in the remaining Agrochemical Companies undertaking R&D are able to discover and develop new and environmentally safe herbicides to provide the tools to contribute to IWM for years to come.

An Overview of Rice Cultivation in Spain and the Management of Herbicide-Resistant Weeds

Spain is the second highest rice-producing country in the European Union, with approximately 105,000 ha used to grow this crop. The major rice-producing regions in Spain are Andalusia, Extremadura, Catalonia, and Valencia, followed by Aragon and Navarre. The main soil texture throughout Spanish rice areas is silty clay loam, with alkaline soils (pH > 7.5)—except in the Extremadura area (pH = 5.5–6)—and a low organic matter content. Water quality in terms of salinity is acceptable, although in some coastal rice areas salinity issues occasionally appear to be a determining factor for high yield achievement. According to a survey carried out on farmers and technicians, the most problematic weeds found in rice crops today in Spain are Echinochloa spp., Leptochloa spp., and Cyperus difformis. Most of the currently authorized herbicides can be classified according to two modes of action: ALS-inhibiting and ACCase-inhibiting. Repeated field applications of herbicides with the same mode of action have resulted in the selection of herbicide-resistant weeds. At present, resistance has been confirmed in different regions of Spain to ALS inhibitors in Echinochloa spp., Leptochloa spp., and Cyperus difformis, and to ACCase inhibitors in Echinochloa spp. and Leptochloa spp. The mechanism of resistance in these species is a mutation in the target site of these herbicides. Several mutations have been found in the ALS gene, both in Echinochloa spp. and Cyperus difformis, distributed in the different rice-growing regions considered in this work. ACCase gene mutations have been mainly found in Leptochloa spp. individuals from Extremadura and Valencia. These different mutations have resulted in different patterns of cross-resistance to ALS- and ACCase-inhibiting herbicides. It is likely that the repeated use of these two modes of action in rice will result in the evolution of more resistant weed populations. The possible availability of new herbicides with alternative modes of action in a short space of time seems very limited, suggesting the need for a more appropriate use of the available alternative strategies (crop rotation, dry sowing, manual weeding, etc.). This work presents a review of the main characteristics of rice cultivation in Spain, emphasizing the current problems in this crop and the management of herbicide-resistant weeds.

Research Progress on Phytopathogenic Fungi and Their Role as Biocontrol Agents.

Phytopathogenic fungi decrease crop yield and quality and cause huge losses in agricultural production. To prevent the occurrence of crop diseases and insect pests, farmers have to use many synthetic chemical pesticides. The extensive use of these pesticides has resulted in a series of environmental and ecological problems, such as the increase in resistant weed populations, soil compaction, and water pollution, which seriously affect the sustainable development of agriculture. This review discusses the main advances in research on plant-pathogenic fungi in terms of their pathogenic factors such as cell wall-degrading enzymes, toxins, growth regulators, effector proteins, and fungal viruses, as well as their application as biocontrol agents for plant pests, diseases, and weeds. Finally, further studies on plant-pathogenic fungal resources with better biocontrol effects can help find new beneficial microbial resources that can control diseases.

Can new herbicide discovery allow weed management to outpace resistance evolution?

While herbicides are the most effective and widely adopted weed management approach, the evolution of multiple herbicide resistance in damaging weed species threatens the yield and profitability of many crops. Weeds accumulate multiple resistance mechanisms through sequential selection and/or gene flow, with long-range and international transport of herbicide-resistant weeds proving to be a serious issue. Metabolic resistance mechanisms can confer resistance across multiple sites of action and even to herbicides not yet discovered. When a new site of action herbicide is introduced to control a key driver weed, it likely will be one of very few effective available herbicide options for that weed in a specific crop due to the continuous use of herbicides over the years and the resulting accumulation of resistance mechanisms, placing it at even higher risk to be rapidly lost to resistance due to the high selection pressure it will experience. The number of available, effective herbicides for certain driver weeds is decreasing over time because the rate of resistance evolution is faster than the rate of new herbicide discovery. Effective monitoring for species movement and diagnostics for resistance should be deployed to rapidly identify emerging resistance to any new site of action. While innovation in herbicide discovery is urgently needed to combat the pressing issue of resistance in weeds, the rate of selection for herbicide resistance in weeds must be slowed through changes in the patterns of how herbicides are used. © 2021 Society of Chemical Industry. © 2021 Society of Chemical Industry.

Trp-574-Leu mutation in wild mustard (Sinapis arvensis L.) as a result of als inhibiting herbicide applications.

Wheat is one of the most important crops grown all around the world. Weeds cause significant yield loss and damage to wheat and their control is generally based on herbicide application. Regular use leads to herbicide resistance in weeds. This study aims to reveal molecular detection of Sinapis arvensis resistance mutation against ALS inhibiting herbicides. For this purpose, survey studies have been carried out in wheat growing areas in Amasya, Çorum, Tokat, and Yozgat provinces and wild mustard seeds have been collected from 310 different fields. According to bioassay tests with tribenuron-methyl, 13 of these populations, have not been affected by the registered dose of herbicide. When survived populations were subjected to dose-effect study and herbicides were applied at 26-fold, the highest and lowest resistance coefficients were determined as 7.2 (A-007) and 1.02 (T-034) respectively. In addition, B domain region from ALS gene was amplified and analyzed in molecular studies to determine point mutation in wild mustard against ALS herbicides. The PCR products were sequenced and target-site mutation to Leucine was observed at Trp-574 amino acide. In the study, point mutation in Trp-574 amino acide and Trp-574 Leu mutation in Sinapis arvensis have been detected for the first time in Turkey.

Glyphosate resistance in Chloris radiata from colombian rice fields involves one target-site mechanism

At present, appearance of herbicide resistant weeds is not new because repeated herbicide treatments per agricultural year/cycle are usual in both perennial and annual crops worldwide. Characterizing resistance mechanisms implied in each herbicide resistant weed is the best tool and the basis to develop integrated weed management (IWM) strategies. The main resistance mechanisms which confer low sensibility to glyphosate in a previously confirmed glyphosate-resistant Chloris radiata population (ChrR), occurring in Colombian rice fields, were characterized. Pure line selection by clone plants showed high resistance levels in ChrR. Comparing with GR50 and LD50 values, ChrR was 9.6 and 10.8 times more resistant with respect to a representative susceptible population (ChrS). The nontarget site mechanisms reduced glyphosate absorption and translocation did not contribute to the glyphosate resistance of the ChrR population. However, enzyme activity assays and DNA sequencing demonstrated that at least one target-site resistance mechanism is involved in such resistance. All ten ChrR plants tested had the amino acid substitution Pro-106-Ser. The results may be crucial to decrease the resistance distribution of C. radiata in Colombia by implementing IWM programs. The change in weed control strategies in rice fields from Colombia must include herbicides with different mode of action from glyphosate and non chemical methods to preserve the useful life of glyphosate longer for weed control in the country.

Seed Germination Ecology of South Eastern Australian Rigid Ryegrass (Lolium rigidum) Populations

Abstract Herbicide resistance is an increasing issue in many weed species, including rigid ryegrass (Lolium rigidum Gaudin); a major weed of winter cropping systems in southern Australia. Recently, this weed has also been found in summer crops in the south eastern region of Australia. Effective control of this herbicide resistant weed across south eastern Australia requires alternative management strategies. These strategies can be informed from analyses on the interaction of germinable seeds with their regional environment and by identifying the differences between populations of varying herbicide resistance levels. In this study, we explore how various environmental factors differentially affect the seed germination and seedling emergence of three L. rigidum populations, including one glyphosate-resistant population (GR), one glyphosate-susceptible population (GS) and one population of unknown resistance status (CC04). Germination was greater than 90% for all populations at each temperature regime except 15/5 C. Populations germinated at a lower rate under 15/5 C, ranging from 74 to 87%. Salt stress had a similar effect on the germination of all populations, with 0% germination occurring at 250 mM salt stress. Population GS had greater tolerance to osmotic stress with 65% germination at −0.4 MPa compared to 47% and 43% germination for CC04 and GR, respectively; however, germination was inhibited at −0.8 and −1.6 MPa for all populations. All populations had lower germination when placed in complete darkness as opposed to alternating light/dark. Germination in darkness was lower for CC04 (69%) than GR (83%) and GS (83%). Seedling emergence declined with increasing burial depth but retained 37% emergence at 8 cm when averaged over the populations. These results indicate that L. rigidum Gaud. can survive under a range of environmental variables and the extent of survival differs based on population, however, there was no difference based on herbicide resistance status.