Cytochrome P450 Herbicide Metabolism as the Main Mechanism of Cross-Resistance to ACCase- and ALS-Inhibitors in Lolium spp. Populations From Argentina: A Molecular Approach in Characterization and Detection

Knowledge about the mechanisms of herbicide resistance provide valuable insights into evolving weed populations in response to selection pressure and should be used as a basis for designing management strategies for herbicide-resistant weeds. The selection pressure associated with reactive management against glyphosate-resistant Lolium spp. populations would have favored the herbicide resistance to ACCase- and ALS-inhibitors. This work was aimed to determine the sensitivity of 80 Argentinean Lolium spp. populations to ALS- and ACCase-inhibitor herbicides for use in wheat or barley and to study the mechanisms of resistance involved. Sensitivity to pinoxaden and iodosulfuron-mesosulfuron were positively correlated (r = 0.84), even though both affect different target sites. Inhibitors of cytochrome P450 monooxygenases (P450s) increased the sensitivity to pinoxaden and iodosulfuron-mesosulfuron in 94% of herbicide-resistant populations and target-site ACCase resistance mutations were detected only in two cases. Polymorphic variants were obtained with a pair primer designed on P450 sequences, cluster analysis discriminated around 80% of susceptible and P450-metabolic resistant plants sampled from a single population or different populations. Five markers corresponding to herbicide sensitivity were identified to be significantly associated with phenotypic variance in plants. Resistance to ALS- and ACCase-inhibitor herbicides were closely related, challenging the rotation of herbicides of both sites of action as a practice against resistance. In that sense, the use of pinoxaden and iodosulfuron-mesosulfuron would have provoked a selection on P450 genes that conduced a convergence of P450-metabolism based resistant Lolium spp. populations, which was detected by markers in a contribution to elucidate the molecular basis of this type of resistance.Fil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Gigón, Ramón. Private Consultant In Weed Control; ArgentinaFil: Larsen, Adelina Olga. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentin

Effects of glyphosate on nodulation and nitrogen fixation of transgenic glyphosate-tolerant soybean

Background: The use of glyphosate on glyphosate-tolerant soybean crops led to improved control of a wide range of weeds, which resulted in reduced costs with the no-till system. The emergence of the first herbicide-resistant weeds have driven an increase in glyphosate applications, and even though those soybean materials have a low sensitivity to glyphosate, the rhizobial symbionts could be affected by the herbicide, and plants might be indirectly injured. Objective: This study aimed to determine the effect of multiple glyphosate applications throughout the soybean crop cycle on plant growth, nodulation and biological nitrogen fixation (BNF). Methods: The effects of one, two and three treatments of a recommended dose of glyphosate on BNF and growth of glyphosate-tolerant soybean plants were evaluated in greenhouse and field experiments. Results: Two or more applications of glyphosate inhibited the BNF and growth of soybean plants. Under controlled conditions, at least one glyphosate application at V1 affected the number and mass of nodules per plant, and successive applications in advanced phonological stages resulted in the inhibition of nodule growth. With two and three sprayings of glyphosate, the proportion of N derived from the air in plants was reduced by 41% compared with the treatment without glyphosate. In field experiments, detrimental effects of three sequential applications of glyphosate on number of nodules per plant (-25%), biomass production (-21%) and grain yield (-36%) were detected. Conclusions: Multiple glyphosate applications of glyphosate inhibited the BNF and growth of soybean plants and it could be as damaging as +weed interference. Nomenclature: Glyphosate; soybean, Glycine max (L.) Merril.Fil: Corral, Raúl Alejandro. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Giaccio, Gustavo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa; Argentin

Evaluación de herbicidas post-emergentes en variedades de trigo candeal

Si bien gran parte de los productores de la zona reconocen al trigo candeal como una interesante alternativa al trigo pan, el manejo de malezas resulta sensiblemente diferente en ambos casos. Existen evidencias que demuestran que el trigo candeal responde de manera diferencial a herbicidas post-emergentes comparado a trigo pan. A su vez, dentro de los posibles herbicidas empleados en trigo candeal, se han detectado diferencias de tolerancia entre cultivares.En función de lo expuesto, surge el objetivo del presente trabajo: evaluar la tolerancia/fitotoxicidad de herbicidas post-emergentes registrados para trigo pan sobre distintas variedades de trigo candeal. Las variedades estudiadas presentaron una tolerancia levemente diferencial a herbicidas post-emergentes evaluados. Sin embargo, tales diferencias no afectaron el rendimiento de alguna variedad en particular. Los herbicidas evaluados resultaron ser seguros para las variedades estudiadas en las condiciones del ensayo, donde se destaca la elevada tolerancia pese a la ocurrencia de heladas en post-aplicación.Fil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Sur; ArgentinaFil: Larsen, Adelina Olga. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Istilart, Carolina María. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentin

¿Cuánto paga una maleza por ser resistente a un herbicida?

La resistencia a herbicidas suele tener un costo energético para las malezas. Esto se traduce en una menor producción de semillas comparado a las plantas susceptibles. El conocimiento de estos aspectos ecológicos permite diseñar estrategias de manejo donde se favorezcan las plantas susceptibles a expensas de las resistentes.EEA BarrowFil: Yanniccari, Marcos. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; ArgentinaFil: Gigón, Ramón. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; ArgentinaFil: Istilart, Carolina Maria. Instituto Nacional de Tecnología Agropecuaria (INTA). Chacra Experimental Integrada Barrow; Argentin

Dynamics of Glyphosate Resistance in Lolium perenne: Pollen-Mediated Gene Flow under Field Conditions in Argentina

The genus Lolium has shown a high tendency to evolve resistance to herbicides. Considering the high level of allogamy of L. perenne and the importance of the wind as an agent for pollen dispersion, the aim of this work was to assess and quantify the effective glyphosate-resistant gene flow by pollen in L. perenne under field conditions. Pollen-mediated gene flow from glyphosate-resistant to -susceptible plants was studied using a donor–receptor design. The results indicate that the effective gene flow reached trap plants distanced ≤35 m downwind from the source of pollen. The progeny of receptor plants growing 0 m from the pollen donors showed 13% of individuals with low glyphosate sensitivity. This represents a seven-fold increase in the frequency of glyphosate-resistant individuals found in the progeny of plants isolated during the flowering period (negative control). Similarly, the progenies of plants grown at 15 and 25 m from the source of glyphosate resistance showed an increase in the frequency of resistant plants by about four- and two-fold, respectively. When the receptor plants were located at >35 m, no glyphosate-resistant plants were detected in their progenies. Management should aim for prevention or delay of flowering of glyphosate-resistant plants.Facultad de Ciencias Agrarias y Forestale

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

Comparação da Sensibilidade ao Glyphosate de Populações de Euphorbia davidii

Euphorbia davidii (Euphorbiaceae) is a summer annual weed present in the Province of Buenos Aires, Argentina. The aim of this study was to compare the sensitivity to glyphosate of different populations of Euphorbia davidii. Twotechniques were used: a seed bioassay and shikimate determination in glyphosa tetreated plants. Germination rates of seeds belonging to the populations from Espartillar, Barrow, Olavarria and Azul exposed to different concentrations of glyphosate were compared. Plants from the same locations treated with glyphosate were evaluated to determine shikimate levels. The most sensitive population was from Espartillar, with a CE50 (average effective concentration) of 4.00 g e.a. L-1. Based on this finding, the resistance index for each population was 1.76, 2.39 and 2.48 for Azul, Olavarria and Barrow respectively. Regarding glyphosate-treated plants in which shikimate levels were determined, a significant increase in the concentration of this metabolite was only observed in the population from Espartillar. Accumulation of shikimate was not detected in the other groups. These results show differential sensitivity to glyphosate of the evaluated populations.Euphorbia davidii (Euphorbiaceae) é uma planta infestante de ciclo anual primaveril-estival presente na Província de Buenos Aires, Argentina. O objetivo deste estudo foi comparar a sensibilidade ao glyphosate de diferentes populações de Euphorbia davidii. Para isso, foram usadas duas técnicas: bioensaio com sementes e determinação dos níveis de chiquimato nas plantas tratadas com glyphosate. Fez-se uma comparação da germinação de sementes de populações provenientes de Espartillar, Barrow, Olavarria e Azul, expostas a diferentes concentrações de glyphosate. Procedeu-se à determinação dos níveis de chiquimato em plantas provenientes das mesmas localidades e tratadas com o herbicida. A população mais sensível foi a de Espartillar, com uma CE50 (concentração efetiva média) de 4,00 g a.e. L-1. Com base neste valor, o índice de resistência de cada local de origem foi de 1,76 , 2,39 e 2,48 para Azul, Olavarría e Barrow, respectivamente. Entre as plantas tratadas, em que os valores de chiquimato foram determinados, observou-se apenas aumento significativo na concentração desse metabólito na população de Espartillar. Nas outras populações não foi identificada qualquer acumulação de chiquimato. Os resultados mostram a sensibilidade diferencial ao glyphosate das populações avaliadas.Fil: Núñez Fré, Federico Roberto. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Juan, Victor Fabian. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Yanniccari, Marcos Ezequiel. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saint André, Horacio María. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Fernandez, R.R.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; Argentin

Cambios de las comunidades de malezas como consecuencia de las rotaciones de cultivos

La rotación de cultivos es una práctica agronómica clave para prevenir y evitar la aparición de malezas resistentes y tolerantes a herbicidasEEA BarrowFil: Istilart, Carolina Maria. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; ArgentinaFil: Forjan, Horacio Jose. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; ArgentinaFil: Manso, Marina Lucrecia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; ArgentinaFil: Yanniccari, Marcos. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Barrow; Argentin

Pérdidas de rendimiento en trigo y cebada asociadas a la interacción con Lolium perenne

La evolución de biotipos resistentes a glifosato, y luego a ciertos graminicidas aplicados en post-emergencia, ya fue demostrada en los últimos años (Diez de Ulzurrun y Leaden, 2012; Yanniccari et al., 2012). Esto complejiza el manejo de la maleza basado únicamente en el control químico donde la frecuencia de escapes se ha incrementado. Como resultado de esto, el ryegrass ha sido una de las malezas comúnmente relevada en la zona, hallándose en interacción con trigo y cebada (Berriolo et al., 2014).Pese a la importancia del complejo Lolium spp. como maleza de ambos cereales de invierno, para los sistemas de producción actuales no se dispone de abundante información regional que muestre el nivel de pérdida en rendimiento y calidad de trigo y cebada como resultado de la interacción con la maleza. El objetivo del trabajo fue determinar el nivel de pérdida de rendimiento y calidad comercial en trigo y cebada provocado por la interacción con Lolium perenne. La maleza interfirió con ambos cultivos conduciendo a la pérdida de alrededor del 25 y 50% del rendimiento en trigo y cebada, respectivamente. Esta caída en el rendimiento no se correspondió con pérdidas en el tamaño de los granos, por tanto se asume que el efecto de la maleza sobre el rendimiento de ambos cereales fue debido a la reducción en el número de granos.Se conoce que el período crítico para la generación del número de granos coincide con el momento de crecimiento activo de las espigas y los tallos hasta el cuajado (aproximadamente 20 días pre-floración y 10 días post-floración). La interferencia generada por la maleza en ese período, explicaría la caída en el número de granos producidos. Principalmente esta interferencia podría estar asociada a la fuerte competencia radical que genera el ryegrass a través de la elevada capacidad de absorción de nitrógeno. Al momento de definirse el peso de los granos (período entre floración y madurez fisiológica), la interferencia del ryegrass no habría llegado a alterar ese componente del rendimiento. En consistencia con esto, tampoco se observaron alteraciones significativas en el porcentaje de proteínas en los granos de trigo ni de cebada. Sin embargo, al comparar valores promedios, una leve caída en el tenor proteico del grano tendría importantes implicancias en la comercialización.Fil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Gigón, Ramón. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Molfese, Elena. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Istilart, Carolina María. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; ArgentinaFil: Astiz, Valentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentin

Cross-resistance to acetyl-CoA carboxylase–inhibiting herbicides conferred by a target-site mutation in perennial ryegrass ( Lolium perenne ) from Argentina

In Argentina, Lolium spp. occur in 40% of winter cereal crops from the Pampas. Several years ago, cases of glyphosate-resistant perennial ryegrass (Lolium perenne L.) were detected, and the use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides to eradicate these plants has been considered. The aim of this study was to evaluate the sensitivity of a putative pinoxaden-resistant L. perenne population to ACCase-inhibiting herbicides. Around 80% of plants from the putative resistant population survived at a recommended dose of pinoxaden, and they produced viable seeds. The resistance indices (RIs) to pinoxaden were 5.1 and 2.8 for plant survival and seed production, respectively. A single point mutation that conferred a Asp-2078-Gly substitution in ACCase was the source of the resistance. To match the plant control achieved in the susceptible population, the resistant population required 5.4- and 10.4-fold greater doses of clethodim and quizalofop, respectively. RIs for viable seed production when treated with clethodim and quizalofop were 3.3 and 6.6, respectively. The Asp-2078-Gly mutation endowed significant levels of resistance to pinoxaden, clethodim, and quizalofop. For three herbicides, the level of resistance of a pinoxaden-resistant L. perenne population to ACCase inhibitors was evaluated, based on an evaluation of dose response for plant survival and seed production. The RIs were higher for plant survival than for seed production. In Argentina, the selection pressure associated with clethodim and haloxifop preplant application and pinoxaden use on wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops, would have favored the propagation of the Asp-2078-Gly mutation with its associated resistance.Fil: Yanniccari, Marcos Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gigón, Ramón. No especifíca