Resistance to glyphosate in Chloris and Parthenium spp. in Latin America. Mechanisms of resistance and alternative control

La incidencia nociva de las malas hierbas constituye uno de los mayores obstáculos para alcanzar producciones agrícolas sustentables, produciendo pérdidas de hasta el 10% y más del 30% de las cosechas en los países desarrollados y en desarrollo, respectivamente. El control de malezas mediante el uso predominante de herbicidas produjo la aparición y difusión exponencial de biotipos tolerantes y resistentes a las principales familias químicas utilizadas. En Latinoamérica desde hace casi 40 años, las poblaciones de malas hierbas están bajo presión de selección continua por el uso de glifosato. Entre las especies que están incrementado en forma significativa su presencia en esta región podemos citar a Parthenium hysterophorus L y el género Chloris. Parthenium hysterophorus L. (Asteraceae, Heliantheae), es una planta herbácea anual o de corta duración nativa de la región del Golfo de México. Es considerada una de las peores malezas debido a su capacidad de invasión, potencial de propagación, impacto económico y sobre la salud humana y el ambiente. Debido a su alto potencial de invadir y perpetuarse sobre suelo no disturbados torna a Parthenium hysterophorus como una seria amenaza en sistemas agrícolas con grandes superficies bajo siembra directa como Brasil y Argentina. Dentro del género Chloris existen al menos 60 especies en Latinoamerica, incluyendo al género Trichloris y otras especies de la tribu de las Chlorideas. Estas especies aumentaron considerablemente su difusión en cultivos perennes, entre ellos los frutales cítricos con amplio uso del herbicida glifosato y en países con amplia adopción del sistema tecnológico siembra directa-soja RR (Roundup Ready)-glifosato, como Brasil y Argentina. Estos sistemas productivos propiciaron el aumento de la presión de selección y por ello, la difusión de biotipos resistentes a este principio activo como Chloris barbata, Chloris elata y Chloris virgata. Estas especies no son homogéneas en cuanto su distribución geográfica, taxonomia ni en su respuesta a herbicidas. Esta situación complica significativamente su estudio y su manejo con alternativas de control eficientes y homogéneas. Por ello, la caracterización morfológica mediante estudios de diferenciación de especies y la determinación de los mecanismos de resistencia al herbicida glifosato constituyen herramientas imprescindibles para poder establecer estrategias de manejo eficientes, integradas y sustentables de Parthenium hysterophorus L y de especies de Chloris presentes en áreas agrícolas de Latinoamérica. En relación a lo anteriormente descripto es que se plantea la justificación del este trabajo de investigación y los objetivos propuestos.The harmful incidence of weeds is one of the biggest obstacles to achieving sustainable agricultural production, producing losses of up to 10% and more than 30% of the harvests in developed and developing countries, respectively. The control of weeds by the predominant use of herbicides produced the appearance and exponential diffusion of tolerant and resistant biotypes to the main chemical families used. In Latin America for almost 40 years, weed populations are under constant selection pressure due to the use of glyphosate. Among the species that are significantly increased their presence in this region we can mention Parthenium hysterophorus L and the genus Chloris. Parthenium hysterophorus L. (Asteraceae, Heliantheae), is an annual or short-lived herbaceous plant native to the Gulf of Mexico region. It is considered one of the worst weeds due to its ability to invade, potential for propagation, economic impact and on human health and the environment. Due to its high potential to invade and perpetuate on undisturbed soil makes Parthenium hysterophorus a serious threat in agricultural systems with large areas under direct seeding such as Brazil and Argentina. Within the genus Chloris there are at least 60 species in Latin America, including the genus Trichloris and other species of the Chlorideas tribe. These species increased considerably their diffusion in perennial crops, among them the citrus fruit trees with ample use of the herbicide glyphosate and in countries with wide adoption of the direct-soybean RR (Roundup Ready) -glyphosate technology package, such as Brazil and Argentina. These productive systems favored the increase of selection pressure and, therefore, the diffusion of biotypes resistant to this active principle such as Chloris barbata, Chloris elata and Chloris virgata. These species are not homogenous in terms of their geographical distribution, taxonomy or in their response to herbicides. This situation significantly complicates its study and its management with efficient and homogeneous control alternatives. Therefore, the morphological characterization through studies of species differentiation and the determination of glyphosate herbicide resistance mechanisms are essential tools to establish efficient, integrated and sustainable management strategies of Parthenium hysterophorus L and Chloris species present in agricultural areas of Latin America. In relation to the previously described is that the rationale of this research work and the objectives proposed

Glyphosate-Resistant Parthenium hysterophorus in the Caribbean Islands: Non Target Site Resistance and Target Site Resistance in Relation to Resistance Levels

Peer reviewedGlyphosate has been the most intensely herbicide used worldwide for decades, and continues to be a single tool for controlling weeds in woody crops. However, the adoption of this herbicide in a wide range of culture systems has led to the emergence of resistant weeds. Glyphosate has been widely used primarily on citrus in the Caribbean area, but a study of resistance in the Caribbean islands of Cuba and the Dominican Republic has never been carried out. Unfortunately, Parthenium hysterophorus has developed glyphosate-resistance in both islands, independently. The resistance level and mechanisms of different P. hysterophorus accessions (three collected in Cuba (Cu-R) and four collected in the Dominican Republic (Do-R) have been studied under greenhouse and laboratory conditions. In in vivo assays (glyphosate dose causing 50% reduction in above-ground vegetative biomass and survival), the resistance factor levels showed susceptible accessions (Cu-S ≥ Do-S), low-resistance accessions (Cu-R3 Do-R2 > Cu-R2 > Do-R3 > Do-R4 > Cu-R3 >> Cu-S ≥ Do-S). Glyphosate was degraded to aminomethylphosphonic acid, glyoxylate and sarcosine by >88% in resistant accessions except in Cu-R3 and Do-R4 resistant accessions (51.12 and 44.21, respectively), whereas a little glyphosate (<9.32%) was degraded in both susceptible accessions at 96 h after treatment. There were significant differences between P. hysterophorus accessions in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity enzyme with and without different glyphosate rates. The R accessions showed values of between 0.026 and 0.21 μmol μg−1 TSP protein min−1 basal EPSPS activity values with respect to the S (0.024 and 0.025) accessions. The same trend was found in the EPSPS enzyme activity treated with glyphosate, where a higher enzyme activity inhibition (glyphosate μM) corresponded to greater resistance levels in P. hysterophorus accessions. One amino acid substitution was found at position 106 in EPSPS, consisting of a proline to serine change in Cu-R1, Do-R1 Do-R2. The above-mentioned results indicate that high resistance values are determined by the number of defense mechanisms (target-site and non-target-site resistance) possessed by the different P. hysterophorus accessions, concurrently.This work was funded by AGL2013-48946-C3-1-R and AGL2016-78944-R projects (Spain).Peer Reviewe

The triple amino acid substitution TAP-IVS in the EPSPS gene confers high glyphosate resistance to the superweed amaranthus hybridus

The introduction of glyphosate-resistant (GR) crops revolutionized weed management; however, the improper use of this technology has selected for a wide range of weeds resistant to glyphosate, referred to as superweeds. We characterized the high glyphosate resistance level of an Amaranthus hybridus population (GRH)—a superweed collected in a GR-soybean field from Cordoba, Argentina—as well as the resistance mechanisms that govern it in comparison to a susceptible population (GSH). The GRH population was 100.6 times more resistant than the GSH population. Reduced absorption and metabolism of glyphosate, as well as gene duplication of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) or its overexpression did not contribute to this resistance. However, GSH plants translocated at least 10% more 14C-glyphosate to the rest of the plant and roots than GRH plants at 9 h after treatment. In addition, a novel triple amino acid substitution from TAP (wild type, GSH) to IVS (triple mutant, GRH) was identified in the EPSPS gene of the GRH. The nucleotide substitutions consisted of ATA102, GTC103 and TCA106 instead of ACA102, GCG103, and CCA106, respectively. The hydrogen bond distances between Gly-101 and Arg-105 positions increased from 2.89 Å (wild type) to 2.93 Å (triple-mutant) according to the EPSPS structural modeling. These results support that the high level of glyphosate resistance of the GRH A. hybridus population was mainly governed by the triple mutation TAP-IVS found of the EPSPS target site, but the impaired translocation of herbicide also contributed in this resistance

Effects of the herbicide glyphosate on non-target plant native species from Chaco forest (Argentina)

Agriculture based on transgenic crops has expanded in Argentina into areas formerly occupied by Chaco forest. Even though glyphosate is the herbicide most widely used in the world, increasing evidence indicates severe ecotoxicological effects on non-target organisms as native plants. The aim of this work is to determine glyphosate effects on 23 native species present in the remaining Chaco forests immersed in agricultural matrices. This is a laboratory/greenhouse approach studying acute effects on seedlings after 21 days. A gradient of glyphosate rates (525, 1050, 2100, 4200, and 8400 g ai/Ha; recommended field application rate (RFAR) = 2100 g ai/Ha) was applied on four-week seedlings cultivated in a greenhouse and response variables (phytotoxicity, growth reduction, and sensitivity to the herbicide) were measured. This gradient of herbicide rates covers realistic rates of glyphosate applications in the crop field and also those that can reach vegetation of forest relicts by off-target drift and overspray. Testing was performed following guidelines for vegetative vigour (post-germination spray). All species showed lethal or sublethal effects after the application of the 25% of RFAR (50% of species showed severe phytotoxicity or death and 70% of species showed growth reduction). The results showed a gradient of sensitivity to glyphosate by which some of the studied species are very sensitive to glyphosate and seedlings died with 25% of RFAR while other species can be classified as herbicide-tolerant. Thus, the vegetation present in the forest relicts could be strongly affected by glyphosate application on crops. Lethal and sublethal effects of glyphosate on non-target plants could promote both the loss of biodiversity in native forest relicts immersed in the agroecosystems and the selection of new crop weeds considering that some biotypes are continuously exposed to low doses of glyphosate.Fil: Ferreira, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Torres, Carolina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Bracamonte, Enzo. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Galetto, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Glyphosate affects the susceptibility of non-target native plant species according to their stage of development and degree of exposure in the landscape

Unsustainable agriculture is producing a great socio-ecological transformation in Latin America because it has expanded into areas occupied by native forests. Glyphosate is the most widely used herbicide, with severe ecotoxicological effects on non-target organisms. The aim of this study was to determine the effects of glyphosate on seedlings of 24 non-target herbaceous and non-herbaceous plant species present in forest relicts of Argentine Chaco. The effects of a gradient of glyphosate doses (525, 1050, 2100, 4200, and 8400 g ai/ha) were measured in seedlings of each species under greenhouse conditions. Seedlings were grown from seeds collected from native forest fragments of different sizes (assuming three different degrees of historical exposure to glyphosate in the landscape). Doses were applied at different stages of seedling development (five- and ten-weeks after emergence), and phytotoxicity, growth reduction, and sensitivity were measured. Glyphosate produced lethal or sublethal effects in all 24 species, some of which were very sensitive (>60 % of the species presented strong to severe growth reduction with ¼ of the dose used on crops). The greatest toxicological effects were related to early stage of development, herbaceous species, and low historical exposure to glyphosate. According to the species sensitivity distribution, the drift-dose to protect 95 % of the plant species that occur in larger forest fragments should not exceed 5 % of the dose commonly used on crops. These results suggest that the current weed management linked to glyphosate-resistant crops could lead to a gradual loss of biodiversity in the landscape. Concurrently, selection of glyphosate-tolerant biotypes in some non-target species could represent a very problematic cycle for the current model of industrial agriculture. Some alternatives for weed control are proposed.Fil: Ferreira, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Torres, Carolina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Bracamonte, Enzo Ricardo. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Galetto, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Valoración de la eficiencia de uso del agua y huella hídrica en cultivos de Vitis vinífera L. en Córdoba, Argentina

Ponencia presentada en 8º Congreso Internacional sobre Gestión y Tratamiento Integral del Agua. Modalidad Virtual, 5, 6, 12 y 13 de Noviembre de 2020.Los objetivos de este trabajo fueron evaluar en Colonia Caroya, Córdoba, la eficiencia de uso del agua de riego (EUA) utilizando el Marco de Evaluación MESMIS, considerando con valor 1(baja eficiencia) a riego por manto y con valor 5 a riego por goteo, cuantificar la Huella Hídrica (HH) verde (v), azul (a) y gris (g) en las variedades de vid Pinot Noir y Malbec (11 ton/ha) e Isabella (14 tn/ha) con diferentes manejo de riego (manto, 60% de eficiencia y goteo, 95% de eficiencia) y establecer estrategias de sustentabilidad de las huellas hídricas obtenidas. Los valores de HH se obtuvieron utilizando el software CROPWAT 8.0 y la metodología propuesta por Hoekstra et al. (2011) y por Cibit et al (2012). Los resultados obtenidos mostraron que los cultivos de vid son ineficientes en el uso del agua de riego y alejado de un valor óptimo de eficiencia local, la HH total requerida es baja en relación a valores nacionales e internacionales. La precipitación efectiva (HHv) utilizada por el cultivo es mayor en relación a valores medios internacionales. La EUA del sistema por goteo representa un 7.6 % del total aportado por el uso de riego por manto. Los resultados evidenciaron que la HHt es insustentable debido al uso de sistemas de riegos tradicionales con baja eficiencia en el uso del agua. En año sin precipitaciones el agua suministrada no cubre las necesidades totales de consumo del cultivo de la vid. El consumo efectivo de agua (HHv) representa el 46% de la oferta anual de agua suministrada. El consumo de agua HHt del cultivo de vid posibilitan el consumo hasta 378 personas para necesidades personales mínimas. Las pérdidas de agua azul del riego por manto y por goteo posibilitan el consumo de 112 y 8 personas para necesidades personales mínimas, respectivamente.Fil: Bracamonte, Enzo Ricardo. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Cátedra de Ecotoxicología; Argentina.Fil: Angulo, Eduardo. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Cátedra de Ecotoxicología; Argentina.Fil: Romero, F. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina.Fil: Bustamante, O. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina.Fil: Casabo, A. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina.Fil: López, L. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina.Fil: Croce, A. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina.Fil: Mattof, Evangelina. Instituto Nacional de Tecnología Agropecuaria. Agencia De Extensión Rural Cordoba; Argentin

From tolerance to resistance: mechanisms governing the differential response to glyphosate in Chloris barbata

Susceptibility and the mechanism (s) governing tolerance/resistance to glyphosate were characterized in two putative-glyphosate-resistant Chloris barbata populations (R1 and R2), collected in Persian lime orchards from Colima State, Mexico, comparing them with one non-treated population (referred to as S). Glyphosate doses required to reduce fresh weight or cause mortality by 50% were 4.2–6.4 times higher in resistant populations than in the S population. The S population accumulated 4.3 and 5.2 times more shikimate than the R2 and R1 popu- lations, respectively. There were no differences in 14 C-glyphosate uptake between R and S populations, but the R plants translo- cated at least 12% less herbicide to the rest of plant and roots 96 h after treatment. Insignificant amounts of glyphosate were metabolized to aminomethyl phosphonate and glyoxylate in both R and S plants. The 5-enolpyruvylshikimate-3-phosphate syn- thase gene of the R populations contained the Pro106-Ser mutation, giving them a resistance 12 (R2) and 14.7 (R1) times greater at target-site level compared with the S population. The Pro106-Ser mutation governs the resistance to glyphosate of the R1 and R2 C barbata populations, but the impaired translocation could contribute to the resistance. These results confirm the first case of glyphosate resistance evolved in this species

Identifying Chloris Species from Cuban Citrus Orchards and Determining Their Glyphosate-Resistance Status

The Chloris genus is a C4 photosynthetic species mainly distributed in tropical and subtropical regions. Populations of three Chloris species occurring in citrus orchards from central Cuba, under long history glyphosate-based weed management, were studied for glyphosate-resistant status by characterizing their herbicide resistance/tolerance mechanisms. Morphological and molecular analyses allowed these species to be identified as C. ciliata Sw., Chloris elata Desv., and Chloris barbata Sw. Based on the glyphosate rate that causes 50% mortality of the treated plants, glyphosate resistance (R) was confirmed only in C. elata, The R population was 6.1-fold more resistant compared to the susceptible (S) population. In addition, R plants of C. elata accumulated 4.6-fold less shikimate after glyphosate application than S plants. Meanwhile, populations of C. barbata and C. ciliata with or without glyphosate application histories showed similar LD50 values and shikimic acid accumulation rates, demonstrating that resistance to glyphosate have not evolved in these species. Plants of R and S populations of C. elata differed in 14C-glyphosate absorption and translocation. The R population exhibited 27.3-fold greater 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) activity than the S population due to a target site mutation corresponding to a Pro-106-Ser substitution found in the EPSPS gene. These reports show the innate tolerance to glyphosate of C. barbata and C. ciliata, and confirm the resistance of C. elata to this herbicide, showing that both non-target site and target-site mechanisms are involved in its resistance to glyphosate. This is the first case of herbicide resistance in Cuba

Reduced absorption and impaired translocation endows glyphosate resistance in Amaranthus palmeri harvested in GR soybean from Argentina

Amaranthus palmeri S. Watson is probably the worst glyphosate-resistant (GR) weed worldwide. The EPSPS (5-enolpyruvylshikimate-3-phosphate-synthase) gene amplification has been reported as the major target-site-resistance (TSR) mechanism conferring resistance to glyphosate in this species. In this study, TSR and non-target-site-resistance (NTSR) mechanisms to glyphosate were characterized in a putative resistant A. palmeri population (GRP), harvested in a GR-soybean crop from Argentina. Glyphosate resistance was confirmed for the GRP population by dose-response assays. No evidence of TSR mechanisms as well as glyphosate metabolism was found in this population. Moreover, a susceptible population (GSP) that absorbed about 10% more herbicide than the GRP population was evaluated at different periods after treatment. The GSP population translocated about 20% more glyphosate to the remainder of the shoots and roots at 96 h after treatment than the control, while the GRP population retained 62% of herbicide in the treated leaves. This is the first case of glyphosate resistance in A. palmeri involving exclusively NTSR mechanisms