Fitness of herbicide-resistant weeds: Current knowledge and implications for management

Herbicide resistance is the ultimate evidence of the extraordinary capacity of weeds to evolve under stressful conditions. Despite the extraordinary plant fitness advantage endowed by herbicide resistance mutations in agroecosystems under herbicide selection, resistance mutations are predicted to exhibit an adaptation cost (i.e., fitness cost), relative to the susceptible wild-type, in herbicide untreated conditions. Fitness costs associated with herbicide resistance mutations are not universal and their expression depends on the particular mutation, genetic background, dominance of the fitness cost, and environmental conditions. The detrimental effects of herbicide resistance mutations on plant fitness may arise as a direct impact on fitness-related traits and/or coevolution with changes in other life history traits that ultimately may lead to fitness costs under particular ecological conditions. This brings the idea that a “lower adaptive value” of herbicide resistance mutations represents an opportunity for the design of resistance management practices that could minimize the evolution of herbicide resistance. It is evident that the challenge for weed management practices aiming to control, minimize, or even reverse the frequency of resistance mutations in the agricultural landscape is to “create” those agroecological conditions that could expose, exploit, and exacerbate those life history and/or fitness traits affecting the evolution of herbicide resistance mutations. Ideally, resistance management should implement a wide range of cultural practices leading to environmentally mediated fitness costs associated with herbicide resistance mutations.Fil: 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. University of Western Australia; Australi

Contrasting plant ecological benefits endowed by naturally occurring EPSPS resistance mutations under glyphosate selection

Concurrent natural evolution of glyphosate resistance single- and double-point EPSPS mutations in weed species provides an opportunity for the estimation of resistance fitness benefits and prediction of equilibrium resistance frequencies in environments under glyphosate selection. Assessment of glyphosate resistance benefit was conducted for the most commonly identified single Pro-106-Ser and less-frequent double TIPS mutations in the EPSPS gene evolved in the global damaging weed Eleusine indica. Under glyphosate selection at the field dose, plants with the single Pro-106-Ser mutation at homozygous state (P106S-rr) showed reduced survival and compromised vegetative growth and fecundity compared with TIPS plants. Whereas both homozygous (TIPS-RR) and compound heterozygous (TIPS-Rr) plants with the double TIPS resistance mutation displayed similar survival rates when exposed to glyphosate, a significantly higher fecundity in the currency of seed number was observed in TIPS-Rr than TIPS-RR plants. The highest plant fitness benefit was associated with the heterozygous TIPS-Rr mutation, whereas plants with the homozygous Pro-106-Ser and TIPS mutations exhibited, respectively, 31% and 39% of the fitness benefit revealed by the TIPS-Rr plants. Populations are predicted to reach stable allelic and genotypic frequencies after 20 years of glyphosate selection at which the WT allele is lost and the stable genotypic polymorphism is comprised by 2% of heterozygous TIPS-Rr, 52% of homozygous TIPS-RR and 46% of homozygous P106S-rr. The high inbreeding nature of E. indica is responsible for the expected frequency decrease in the fittest TIPS-Rr in favour of the homozygous TIPS-RR and P106S-rr. Mutated alleles associated with the glyphosate resistance EPSPS single EPSPS Pro-106-Ser and double TIPS mutations confer contrasting fitness benefits to E. indica under glyphosate treatment and therefore are expected to exhibit contrasting evolution rates in cropping systems under recurrent glyphosate selection.Fil: 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. University of Western Australia; AustraliaFil: Han, Heping. University of Western Australia; AustraliaFil: Yu, Qin. University of Western Australia; AustraliaFil: García, Federico. 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; ArgentinaFil: Powles, Stephen B.. University of Western Australia; Australi

Physiological Fitness Cost Associated with Glyphosate Resistance in Echinochloa colona: Seed Germination Ecology

The expression of fitness cost associated with herbicide resistance in weeds is not universal and may vary during different life stages. Hence, an analysis of the fitness cost of a glyphosate-resistant Echinochloa colona at the seed stage was conducted. Seed germination ecology of glyphosate-susceptible and - resistant E. colona was studied to examine the physiological fitness cost between the S (susceptible) and R (resistant) phenotypes. The plant material was selected from within one segregating glyphosateresistant E. colona population to minimise allelic interference from other fitness-related loci. Experiments were conducted in a growth incubator at alternating temperatures of 30/20C day/night with a 12-h photoperiod. Seed dormancy and germination were also tested under constant darkness at the same temperature regime. Seeds of both the S and R phenotypes kept at warmer temperatures (after-ripening dry storage at 15 to 35C) or on the ground surface outdoors for 14 days, germinated better (with more than 95% of seeds had germinated) than those seeds (about 20% germination) that were kept at lower temperature (8C) for the same period of storage. Light and longer dry after-ripening times increased the rate of seed dormancy release and germination (almost 100% seed germination) for both the S and R phenotypes. Equal decline in seedling emergence in both the S and R phenotypes was evident with increasing soil burial depth (P > 0.05). Thus, the S and R phenotypes exhibited similar characteristics of seed dormancy release, germination and seedling emergence. As there is lack of physiological fitness cost in the R phenotype of E. colona at the seed and early seedling stage, it remains a challenge to develop specific control measures for the R phenotype. An alternative herbicide with different mode of action should be integrated with other weed management approach such as cultural, mechanical and biological control to reduce sole reliance of glyphosate in controlling the R phenotype of this E. colona population.Fil: Sheng Goh, Sou. The Malaysian Rubber Board; MalasiaFil: 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; ArgentinaFil: Busi, Roberto. University of Western Australia; AustraliaFil: Goggin, Danica. University of Western Australia; AustraliaFil: Powles, Stephen B.. University of Western Australia; Australi

Global patterns of herbicide resistance evolution in Amaranthus spp.: an analysis comparing species, cropping regions and herbicides

Herbicide resistance in weeds is an evolutionary process. Although there is a great global diversity of weeds, independent origins of herbicide resistance evolution have been shown to converge into similar molecular and physiological resistance mechanisms in geographically distant weed populations. Amaranthus species have shown an extraordinary ability to evolve herbicide resistance and invade new environments at a global scale, which represents an opportunity for identifying adaptive evolutionary patterns. The most frequent cases of herbicide-resistant Amaranthus species have been identified in North America, where A. hybridus, A. palmeri, A. tuberculatus and A. retroflexus comprise more than 90% of them. Meanwhile, A. retroflexus, A. hybridus and A. palmeri have been the most reported species in South America. Around 70% of the cases of herbicide-resistant Amaranthus species have been identified in global soybean and corn crops. The higher fecundity and adaptability of plants to a broad range of environments would make populations more likely to persist and be selected for herbicide resistance. Co-evolution of multiple herbicide resistance mechanisms at the plant and/or population level is evident in weed species. For Amaranthus spp., resistance cases highlight evolutionary responses to herbicide use with clear patterns of selection for multiple herbicide resistance in particular regions and spread to new areas within and between global cropping systems. Seed-mediated gene flow is an important component to the spread of herbicide resistant Amaranthus spp. populations. Reduction of the intensity of herbicide selection by combining diverse and integrated weed control practices should be a common goal in weed management programs.Fil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gaines, Todd. University of Colorado; Estados UnidosFil: Scursoni, Julio Alejandro. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: De Prado, Rafael. Universidad de Córdoba; EspañaFil: 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; Argentin

Glyphosate resistance in perennial Sorghum halepense (Johnsongrass), endowed by reduced glyphosate translocation and leaf uptake

Background: In a large cropping area of northern Argentina, Sorghum halepense (Johnsongrass) has evolved towards glyphosate resistance. This study aimed to determine the molecular and biochemical basis conferring glyphosate resistance in this species. Experiments were conducted to assess target EPSPS gene sequences and 14C-glyphosate leaf absorption and translocation to meristematic tissues. Results: Individuals of all resistant (R) accessions exhibited significantly less glyphosate translocation to root (11% versus 29%) and stem (9% versus 26%) meristems when compared with susceptible (S) plants. A notably higher proportion of the applied glyphosate remained in the treated leaves of R plants (63%) than in the treated leaves of S plants (27%). In addition, individuals of S. halepense accession R 2 consistently showed lower glyphosate absorption rates in both adaxial (10-20%) and abaxial (20-25%) leaf surfaces compared with S plants. No glyphosate resistance endowing mutations in the EPSPS gene at Pro-101-106 residues were found in any of the evaluated R accessions. Conclusion: The results of the present investigation indicate that reduced glyphosate translocation to meristems is the primary mechanism endowing glyphosate resistance in S. halepense from cropping fields in Argentina. To a lesser extent, reduced glyphosate leaf uptake has also been shown to be involved in glyphosate-resistant S. halepense.Fil: 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; ArgentinaFil: Balbi, María C.. No especifíca;Fil: Distéfano, Ana J.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; Argentina. Universidad de Buenos Aires; ArgentinaFil: Fernández, Luis. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; ArgentinaFil: Hopp, Esteban. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; Argentina. Universidad de Buenos Aires; ArgentinaFil: Yu, Qin. University of Western Australia; AustraliaFil: Powles, Stephen B.. University of Western Australia; Australi

Investigating the origins and evolution of a glyphosate-resistant weed invasion in South America

The global invasion, and subsequent spread and evolution of weeds provides unique opportunities to address fundamental questions in evolutionary and invasion ecology. Amaranthus palmeri is a widespread glyphosate-resistant (GR) weed in the USA. Since 2015, GR populations of A. palmeri have been confirmed in South America, raising questions about introduction pathways and the importance of pre- vs. post-invasion evolution of GR traits. We used RAD-sequencing genotyping to characterize genetic structure of populations from Brazil, Argentina, Uruguay and the USA. We also quantified gene copy number of the glyphosate target, 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS), and the presence of an extrachromosomal circular DNA (eccDNA) replicon known to confer glyphosate resistance in USA populations. Populations in Brazil, Argentina and Uruguay were only weakly differentiated (pairwise FST ≤0.043) in comparison to USA populations (mean pairwise FST =0.161, range =0.068–0.258), suggesting a single major invasion event. However, elevated EPSPS copy number and the EPSPS replicon were identified in all populations from Brazil and Uruguay, but only in a single Argentinean population. These observations are consistent with independent in situ evolution of glyphosate resistance in Argentina, followed by some limited recent migration of the eccDNA-based mechanism from Brazil to Argentina. Taken together, our results are consistent with an initial introduction of A. palmeri into South America sometime before the 1980s, and local evolution of GR in Argentina, followed by a secondary invasion of GR A. palmeri with the unique eccDNA-based mechanism from the USA into Brazil and Uruguay during the 2010s.Fil: Gaines, Todd A. State University of Colorado - Fort Collins; Estados UnidosFil: Slavov, Gancho. No especifíca;Fil: Hughes, David. No especifíca;Fil: Kupper, Anita. State University of Colorado - Fort Collins; Estados UnidosFil: Sparks, Crystal. State University of Colorado - Fort Collins; Estados UnidosFil: Oliva, Julian. Universidad Católica de Córdoba; ArgentinaFil: 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; ArgentinaFil: García, Alejandro Marcelo. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Merotto, Aldo. Universidade Federal do Rio Grande do Sul; BrasilFil: Neve, Paul. No especifíca

Respuesta a herbicidas con diferentes modos de acción (HRAC) en poblaciones de Amaranthus hybridus L. de la Argentina

Amaranthus hybridus L. (yuyo colorado) es actualmente una de las especies maleza más problemáticas en los sistemas de producción de cultivos primavera estivales. Durante diciembre y febrero (2018-2019) se estudió en la Facultad de Ciencias Agrarias de la UNR y la Facultad de Agronomía de la UBA, la respuesta a distintos herbicidas de 50 poblaciones de A. hybridus. Los individuos de cada una de las poblaciones estudiadas se obtuvieron a partir de semillas cosechadas en lotes de producción de soja de diferentes áreas de producción, durante la campaña 2017-18. Se evaluó la respuesta a 2,4-D (1140 g e.a. ha-1), dicamba (560 g e.a. ha-1), fomesafén (250 g ha-1), topramezone (34 g ha-1) y glifosato (1080 g e.a. ha-1). Los herbicidas se aplicaron en cabina estática con un volumen de 140 l ha-1 y sobre plantas entre 2 a 6 hojas. A los 30 días de aplicados se cuantificó la supervivencia de individuos para cada tratamiento. En el conjunto de las poblaciones 84% y 76% fueron absolutamente susceptibles (supervivencia 0%) a 2,4-D y dicamba, respectivamente. No se identificaron poblaciones absolutamente susceptibles a los otros herbicidas evaluados. El 43%, 72% y 82% de las poblaciones presentaron supervivencia mayor a 60% a fomesafén, topramezone y glifosato, respectivamente. Más del 90% de las poblaciones presentaron elevados valores de supervivencia a glifosato, sin embargo, siguen encontrándose algunas susceptibles. Las diferencias en los valores de supervivencia permiten inferir la existencia de variabilidad genética para estos modos de acción, sobre la que podrían actuar los herbicidas, promoviendo procesos de selección de resistencia. Los resultados obtenidos sugieren la necesidad prioritaria de aplicar otras prácticas de manejo culturales que conserven la utilidad y la eficacia de los diferentes herbicidas, particularmente de los auxínicos.Amaranthus hybridus L. (pigweed) is currently one of the most problematic weed species in spring-summer crop production systems During December and February (2018-19) the response to different herbicides from fifty populations of A. hybridus was studied at the Faculty of Agronomy (UNR) and the Faculty of Agronomy (UBA). Individuals from each of the studied populations were obtai - ned from seeds harvested in soybean fields from different production areas, during the 2017-18 season. The response to 2,4-D (1140 g e. a.ha-1), Dicamba (560 g e.a. ha-1), Fomesafén (250 g ha-1), Topramezone (34 g ha-1) and Glyphosate (1080 g e.a. ha-1) were evaluated. Herbi - cides were applied in a static cabin with volume of 140 l ha-1 and 30 days after application, the survival of individuals was quantified for each treatment. In all the populations, 84% and 76% were absolutely susceptible (survival 0%) to 2,4-D and Dicamba, respectively. There were not totally susceptible populations to the other herbicides evaluated. The 43%, 72% and 82% of the populations presented survival greater than 60% to fomesafén, topramezone and glyphosate, respectively. More than 90% of the populations presented high glyphosate survival values, however some susceptible ones are still found. The differences in survival values allow us to infer the existence of genetic variability for these modes of action, on which herbicides could act, promoting resistance selection processes. The results obtained suggest the priority to apply management practices that preserve the usefulness and efficacy of different herbicides, particularly auxinics.Fil: Scursoni, Julio Alejandro. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: 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; ArgentinaFil: Tuesca, Daniel Horacio. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Balassone, Federico Emmanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Morello, Juan Pablo. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Medina Herrera, Daniela. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Lescano Martinez, María Cecilia. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Montero Bulacio, Nicolás. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Crespo, Roberto Javier. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; ArgentinaFil: Depetris, María Rosa. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentin

Experimental methods for estimation of plant fitness costs associated with herbicide-resistance genes

Since the beginning of agriculture, crops have been exposed to recurrent invasion by weeds that can impose severe reductions in crop quality and yield. There have been continuing efforts to reduce the impacts of weeds on production. More than 40 yr ago, overreliance on herbicide technology to reduce weed infestations resulted in the selection of adaptive traits that enabled weed survival and reproduction under herbicide treatments. As a result, herbicide resistance in > 200 weed species has evolved worldwide.Fil: 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; ArgentinaFil: Gundel, Pedro Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Preston, Christopher. University of Adelaide. School of Agriculture, Food and Wine; Australi

Genetic inheritance of cytochrome P450-mediated metabolic resistance to chlorsulfuron in a multiple herbicide resistant Lolium rigidum population

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 14reciprocal 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.Fil: Han, H.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; AustraliaFil: Yu, Q.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; AustraliaFil: 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; ArgentinaFil: Powles, S. B.. University of Western Australia. School of Plant Biology. Australian Herbicide Resistance Initiative; Australi

AHAS herbicide resistance endowing mutations: Effect on AHAS functionality and plant growth

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.Fil: Yu, Qin. University of Western Australia; AustraliaFil: Han, Heping. University of Western Australia; AustraliaFil: 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; ArgentinaFil: Powles, Stephen B.. University of Western Australia; Australi