Abstract:

Author affiliation: Murray, Justine V.. Water for Healthy Country Flagship; Australia

Author affiliation: Lehnhoff, Erik A.. Montana State University; Estados Unidos

Author affiliation: Neve, Paul. University of Warwick; Reino Unido

Author affiliation: Poggio, Santiago Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Author affiliation: Webber, Bruce L.. CSIRO Ecosystems Sciences; Australia. The University of Western Australia; Australia

Abstract:

Twenty-two amino acid substitutions at seven conserved amino acid residues in the acetohydroxyacid synthase (AHAS) gene have been identified to date that confer target-site resistance to AHAS-inhibiting herbicides in biotypes of field-evolved resistant weed species. However, the effect of resistance mutations on AHAS functionality and plant growth has been investigated for only a very few mutations. This research investigates the effect of various AHAS resistance mutations in Lolium rigidum on AHAS functionality and plant growth. The enzyme kinetics of AHAS from five purified L. rigidum populations, each homozygous for the resistance mutations Pro-197-Ala, Pro-197-Arg, Pro-197-Gln, Pro-197-Ser or Trp-574-Leu, were characterized and the pleiotropic effect of three mutations on plant growth was assessed via relative growth rate analysis. All these resistance mutations endowed a herbicide-resistant AHAS and most resulted in higher extractable AHAS activity, with no-to-minor changes in AHAS kinetics. The Pro-197-Arg mutation slightly (but significantly) increased the Km for pyruvate and remarkably increased sensitivity to feedback inhibition by branched chain amino acids. Whereas the Pro-197-Ser and Trp-574-Leu mutations exhibited no significant effects on plant growth, the Pro-197-Arg mutation resulted in lower growth rates. It is clear that, at least in L. rigidum, these five AHAS resistance mutations have no major impact on AHAS functionality and hence probably no plant resistance costs. These results, in part, explain why so many Pro-197 AHAS resistance mutations in AHAS have evolved and why the Pro-197-Ser and the Trp-574-Leu AHAS resistance mutations are frequently found in many weed species.

Author affiliation: Yu, Qin. University of Western Australia; Australia

Author affiliation: Han, Heping. University of Western Australia; Australia

Author affiliation: Vila Aiub, Martin Miguel. University of Western Australia; Australia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Author affiliation: Powles, Stephen B.. University of Western Australia; Australia

Abstract:

BACKGROUND: Soon after the commercial release of sunflower cultivars resistant to imidazolinone herbicides, several uncontrolled feral radish (Raphanus sativus L.) populations were found in south-eastern Buenos Aires, Argentina. These populations were studied in field, glasshouse and laboratory experiments aiming to characterise their resistance profile and to develop management tools. RESULTS: Three feral radish accessions were highly resistant to ten active ingredients of five families of acetohydroxyacid synthase (AHAS)-inhibiting herbicides. Sequence analysis of the AHAS gene detected a Trp574Leu mutation in all resistant accessions. One accession with an intermediate level of resistance was heterozygous for this mutation, probably owing to gene exchange with a susceptible subpopulation located in the field margin. Herbicide-resistant and herbicide-susceptible radish could be controlled in sunflower by alternative herbicides. CONCLUSION: This is the first report of feral radish with resistance to herbicides belonging to all the AHAS-inhibiting herbicide families, conferred by Trp574Leu mutation in the AHAS gene. An appropriate herbicide rotation with alternative herbicides such as fluorochloridone or aclonifen and anincreasein the diversity of cropping systems areimportant forminimising the prevalence of these biotypes. resistance profile and to develop management tools.

Author affiliation: Pandolfo, Claudio Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Author affiliation: Presotto, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Author affiliation: Moreno, Florencia. Badische Anilin und Soda Fabrik; Argentina

Author affiliation: Dossou, Ida. DNA LandMarks; Canadá

Author affiliation: Migasso, Juan Pablo. Badische Anilin und Soda Fabrik; Argentina

Author affiliation: Sakima, Ernesto. Badische Anilin und Soda Fabrik; Argentina

Author affiliation: Cantamutto, Miguel Ángel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Abstract:

The potential for human-driven evolution in economically and environmentally important organisms in medicine, agriculture and conservation management is now widely recognised. The evolution of herbicide resistance in weeds is a classic example of rapid adaptation in the face of human-mediated selection. Management strategies that aim to slow or prevent the evolution of herbicide resistance must be informed by an understanding of the ecological and evolutionary factors that drive selection in weed populations. Here, we argue for a greater focus on the ultimate causes of selection for resistance in herbicide resistance studies. The emerging fields of eco-evolutionary dynamics and applied evolutionary biology offer ameans to achieve this goal and to consider herbicide resistance in a broader and sometimes novel context. Four relevant research questions are presented, which examine (i) the impact of herbicide dose on selection for resistance, (ii) plant fitness in herbicide resistance studies, (iii) the efficacy of herbicide rotations and mixtures and (iv) the impacts of gene flow on resistance evolution and spread. In all cases, fundamental ecology and evolution have the potential to offer new insights into herbicide resistance evolution and management.

Author affiliation: Neve, Paul. University of Warwick. School of Life Sciences; Reino Unido

Author affiliation: Busi, Roberto. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Author affiliation: Renton, Michael. University of Western Australia. School of Plant Biology; Australia

Author affiliation: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. University of Western Australia. School of Plant Biology; Australia

Abstract:

BACKGROUND: In the Mediterranean area, Lolium species have evolved resistance to glyphosate after decades of continual use without other alternative chemicals in perennial crops (olive, citrus and vineyards). In recent years, oxyfluorfen alone or mixed with glyphosate and glufosinate has been introduced as a chemical option to control dicot and grass weeds. RESULTS: Dose-response studies confirmed that three glyphosate-resistant Lolium weed species (L. rigidum, L. perenne, L. multiflorum) collected from perennial crops in the Iberian Peninsula have also evolved resistance to glufosinate and oxyfluorfen herbicides, despite their recent introduction. Based on the LD50 resistance parameter, the resistance factor was similar among Lolium species and ranged from 14- to 21-fold and from ten- to 12-fold for oxyfluorfen and glufosinate respectively. Similarly, about 14-fold resistance to both oxyfluorfen and glufosinate was estimated on average for the three Lolium species when growth reduction (GR50) was assessed. This study identified oxyfluorfen resistance in a grass species for the first time. CONCLUSION: A major threat to sustainability of perennial crops in the Iberian Peninsula is evident, as multiple resistance to non-selective glyphosate, glufosinate and oxyfluorfen herbicides has evolved in L. rigidum, L. perenne and L. multiflorum weeds.

Author affiliation: Fernández, Pablo. Universidad de Córdoba; España

Author affiliation: Alcántara, Ricardo. Universidad de Córdoba; España

Author affiliation: Osuna, María D. Centro de Investigaciones Científicas y Tecnológicas de Extremadura; España

Author affiliation: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Author affiliation: Prado, Rafael De. Universidad de Córdoba; España

Abstract:

Field evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in a multiple resistant Lolium rigidum population (VLR69) is known to be mainly due to enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases. The present study investigates genetic inheritance of P450-mediated metabolic resistance to the ALS-inhibiting herbicide chlorsulfuron. To this end, a P450-mediated, metabolism-based resistant sub-set of VLR69 was carefully selected using plant vegetative cloning, appropriate herbicide screen test and the known P450 inhibitor malathion. Both intermediate and near-dominant nuclear-encoded phenotypic resistance traits were observed in 14<br />reciprocal F1 families. The segregation of phenotypic chlorsulfuron resistance in j-F2 families was analysed using genetic inheritance models involving one or two loci. The results from four j-F2 families revealed complex patterns of genetic inheritance of P450-mediated metabolic resistance in genetically diverse and cross-pollinated species L. rigidum: multiple loci are likely involved and interact with herbicide rates and environmental conditions in mediating the resistance phenotype.

Author affiliation: Han, H.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Author affiliation: Yu, Q.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Author affiliation: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Author affiliation: Powles, S. B.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Abstract:

Synthetic herbicides have been used globally to control weeds in major field crops. This has imposed a strong selection for any trait that enables plant populations to survive and reproduce in the presence of the herbicide. Herbicide resistance in weeds must be minimized because it is a major limiting factor to food security in global agriculture. This represents a huge challenge that will require great research efforts to develop control strategies as alternatives to the dominant and almost exclusive practice of weed control by herbicides. Weed scientists, plant ecologists and evolutionary biologists should join forces and work towards an improved and more integrated understanding of resistance across all scales. This approach will likely facilitate the design of innovative solutions to the global herbicide resistance challenge.

Author affiliation: Busi, Roberto. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina; University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Beckie, Hugh J.. Agriculture and Agri-Food Canada. Saskatoon Research Centre; Canadá;

Author affiliation: Gaines, Todd A.. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Goggin, Danica E.. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Kaundun, Shiv S.. Syngenta. Biology and Logistics; Reino Unido;

Author affiliation: Lacoste, Myrtille. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Neve, Paul. University of Warwick. School of Life Sciences; Reino Unido;

Author affiliation: Nissen, Scott J.. Colorado State University. Department of Bioagricultural Sciences and Pest Management; Estados Unidos de América;

Author affiliation: Norsworthy, Jason K.. University of Arkansas. Crop, Soil and Environmental Sciences Department (Weed Science); Estados Unidos de América;

Author affiliation: Renton, Michael. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Shaner, Dave L.. United States Department of Agriculture. Agricultural Research Service; Estados Unidos de América;

Author affiliation: Tranel, Patrick J.. University of Illinois. Department of Crop Science; Estados Unidos de América;

Author affiliation: Wright, Terry. Dow AgroSciences. Intellectual Property Portfolio Development; Estados Unidos de América;

Author affiliation: Yu, Quin. University of Western Australia. School of Plant Biology; Australia;

Author affiliation: Powles, Stephen B.. University of Western Australia. School of Plant Biology; Australia;

Abstract:

Agricultural weeds have rapidly adapted to intensive herbicide selection and resistance to herbicides has evolved within ecological timescales. Yet, the genetic basis of broad-spectrum generalist herbicide resistance is largely unknown. This study aims to determine the genetic control of non-target-site herbicide resistance trait(s) that rapidly evolved under recurrent selection of the novel lipid biosynthesis inhibitor pyroxasulfone in Lolium rigidum. The phenotypic segregation of pyroxasulfone resistance in parental, F1 and back-cross (BC) families was assessed in plants exposed to a gradient of pyroxasulfone doses. The inheritance of resistance to chemically dissimilar herbicides (cross-resistance) was also evaluated. Evolved resistance to the novel selective agent (pyroxasulfone) is explained by Mendelian segregation of one semi-dominant allele incrementally herbicide-selected at higher frequency in the progeny. In BC families, cross-resistance is conferred by an incompletely dominant single major locus. This study confirms that herbicide resistance can rapidly evolve to any novel selective herbicide agents by continuous and repeated herbicide use. The results imply that the combination of herbicide options (rotation, mixtures or combinations) to exploit incomplete dominance can provide acceptable control of broad-spectrum generalist resistance-endowing monogenic traits. Herbicide diversity within a set of integrated management tactics can be one important component to reduce the herbicide selection intensity.

Author affiliation: Busi, Roberto. University Of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Author affiliation: Gaines, Todd A.. University Of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Author affiliation: Vila Aiub, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Author affiliation: Powles, Stephen B.. University Of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australia

Abstract:

Radish has developed feral and weedy biotypes, which is a concern for agriculturearound the world. In Argentina, it is one of the most widespread and troublesome crop weeds. In Brazil, this species has developed herbicide-resistance to acetohydroxyacid synthase (AHAS) inhibiting herbicides. The objective of this study was to record the presence of herbicide-resistant weedy radish plants in Argentina. In spring 2008, we found a small population of radish at the end of the flowering stage in an imidazolinone-tolerant canolafield treated with imazethapyr. Screening and dose-response tests were conducted to two successive generations. They proved the biotype resistant status, and showed extensive survival (between 50 and 80% of control) to the application of a double dose of four AHAS-inhibiting herbicides from two different chemical families (imidazolinones and sulfonylureas). Dose-response assays exhibited very high resistance for imazethapyr (LD50 = 2452.5 g a.i. ha-1, GR50 = 2926.9 g a.i. ha-1) and intermediate for metsulfuron (LD50 = 3.0 g a.i. ha-1, GR50 = 43.2 g a.i. ha-1). The acquisition of cross-resistance to different herbicide families would confer an adaptive and invasive advantage in agricultural environments to this biotype. Due to the herbicide rotation conducted in the field, thedispersion of this biotype was restricted. This is the first report of resistance in weedy radish in Argentina.

O nabo tornou-se feral, sendo uma preocupação para a agricultura em diversas partes do mundo. Na Argentina, é uma das plantas daninhas mais difundidas e problemáticas das culturas. No Brasil, essa espécie gerou biótipos resistentes aos herbicidas inibidores de AHAS. O objetivo deste estudo foi documentar a presença de nabo-silvestre com resistência na Argentina. Na primavera de 2008, observaram-se plantas de nabo nos últimos estádios de floração em um campo de canola tolerante aos herbicidas do grupo químico das imidazolinonas, que havia recebido uma aplicação de imazethapyr. Testes de rastreio e dose-resposta foram conduzidos por duas gerações sucessivas, os quais provaram o status de biótipo resistente e mostraram alta sobrevivência (entre 50 e 80% de controle) na aplicação de dose dupla de quatro herbicidas inibidores da AHAS (duas famílias químicas diferentes: imidazolinonas e sulfonilureias). Os ensaios de dose-resposta exibiram resistência muito elevada para imazethapyr (LD50 = 2.452,5 g i.a. ha-1, GR50 = 2.926,9 g i.a. ha-1) e intermediária para metsulfuron (LD50 = 3.0 g i.a. ha-1, GR50 = 43.2 g i.a. ha-1). A aquisição de resistência cruzada para famílias de herbicidas diferentes proporcionaria uma vantagem adaptativa e invasiva em ambientes agrícolas para esse biótipo. Devido à rotação do herbicida conduzida no campo, a dispersão desse biótipo foi restringida. Esse é o primeiro relato de resistência em nabo-silvestre para a Argentina.

Author affiliation: Pandolfo, Claudio Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Author affiliation: Presotto, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Author affiliation: Poverene, Maria Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Author affiliation: Cantamutto, Lucía Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Abstract:

A 2,4-D-resistant tall waterhemp population (FS) from Nebraska was evaluated for resistance to other TIR1 auxin receptor herbicides and to herbicides having alternative mechanisms of action using greenhouse bioassays and genetic markers. Atrazine, imazethapyr, lactofen, mesotrione, glufosinate, and glyphosate were applied in a single-dose bioassay, and tissue was collected from marked plants for genetic analysis. The FS population was not injured by atrazine or by imazethapyr. Approximately 50% of the plants survived lactofen and were actively growing 28 d after treatment. The population was susceptible to mesotrione, glufosinate, and glyphosate. Ametryn, chlorimuron-ethyl, 2,4-D, aminocyclopyraclor, aminopyralid, and picloram were applied in dose - response studies. The FS population was sensitive to ametryn, and the Ser-264-Gly substitution in the D1 protein was not detected, suggesting the lack of response to atrazine is not due to a target-site mutation. The FS population exhibited less than 50% injury to chlorimuron-ethyl at application rates 20 times the labeled use rate. The Ser-653-Asn acetolactate synthase (ALS) substitution, which confers resistance to imidazolinone herbicides, was present in the FS population. However, this does not explain the lack of response to the sulfonylurea herbicide, chlorimuron-ethyl. Sequencing of a portion of the PPX2L gene did not show the ΔG210 mutation that confers resistance to protoporphyrinogen oxidase - inhibiting herbicides, suggesting that other factors were responsible for waterhemp survival after lactofen application. The FS population was confirmed to be at least 30-fold resistant to 2,4-D relative to the susceptible populations. In addition, it was at least 3-fold less sensitive to aminopyralid and picloram, two other TIR1 auxin receptor herbicides, than the 2,4-D-susceptible populations were. These data indicated that the FS population contains both target and non - target site mechanisms conferring resistance to herbicides spanning at least three mechanisms of action: TIR1 auxin receptors, ALS inhibitors, and photosystem II inhibitors.

Author affiliation: Crespo, Roberto Javier. University of Nebraska; Estados Unidos

Author affiliation: Wingeyer, Ana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Entre Ríos. Estación Experimental Agropecuaria Paraná; Argentina

Author affiliation: Kruger, Greg R.. University of Nebraska; Estados Unidos

Author affiliation: Riggins, Chance W.. University of Illinois at Urbana; Estados Unidos

Author affiliation: Tranel, Patrick J.. University of Illinois at Urbana; Estados Unidos

Author affiliation: Bernards, Mark L.. University of Nebraska; Estados Unidos