RESUMO
The characterization of the mechanisms conferring resistance to herbicides in weeds is essential for developing effective management programs. This study was focused on characterizing the resistance level and the main mechanisms that confer resistance to glyphosate in a resistant (R) Steinchisma laxum population collected in a Colombian rice field in 2020. The R population exhibited 11.2 times higher resistance compared to a susceptible (S) population. Non-target site resistance (NTSR) mechanisms that reduced absorption and impaired translocation and glyphosate metabolism were not involved in the resistance to glyphosate in the R population. Evaluating the target site resistance mechanisms by means of enzymatic activity assays and EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene sequencing, the mutation Pro106Ser was found in R plants of S. laxum. These findings are crucial for managing the spread of S. laxum resistance in Colombia. To effectively control S. laxum in the future, it is imperative that farmers use herbicides with different mechanisms of action in addition to glyphosate and adopt Integrate Management Programs to control weeds in rice fields of the central valleys of Colombia.
RESUMO
Bromus catharticus Vahl. has been used as a valuable forage crop, but it has also been noted as a weed of winter crops and an invader in several countries. In Argentina, a putative glyphosate-resistant population of B. catharticus was identified as a consequence of the lack of effective control with glyphosate in the pre-sowing of wheat. Plant survival and shikimate accumulation analysis demonstrated a lower glyphosate-sensitivity of this population in comparison to a susceptible B. catharticus population. The resistant population was 4-fold more resistant to glyphosate than its susceptible counterpart. There was no evidence of target-site mechanisms of glyphosate resistance or an enhanced capacity to metabolize glyphosate in the resistant population. However, the resistant plants showed a lower foliar retention of glyphosate (138.34 µl solution g-1 dry weight vs. 390.79 µl solution g-1 dry weight), a reduced absorption of 14C-glyphosate (54.18 vs. 73.56%) and lower translocation of 14C-glyphosate from the labeled leaf (27.70 vs. 62.36%). As a result, susceptible plants accumulated a 4.1-fold higher concentration of 14C-glyphosate in the roots compared to resistant plants. The current work describes the first worldwide case of glyphosate resistance in B. catharticus. A reduced foliar retention of herbicide, a differential rate of glyphosate entry into leaves and an altered glyphosate translocation pattern would be the most likely mechanisms of glyphosate exclusion.
RESUMO
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.
Assuntos
3-Fosfoshikimato 1-Carboxiviniltransferase/genética , Amaranthus/efeitos dos fármacos , Amaranthus/genética , Substituição de Aminoácidos , Glicina/análogos & derivados , Resistência a Herbicidas/genética , Herbicidas/farmacologia , Argentina , Relação Dose-Resposta a Droga , Duplicação Gênica , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Glicina/metabolismo , Glicina/farmacologia , Mutação/efeitos dos fármacos , Fosfatos/metabolismo , Proteínas de Plantas/metabolismo , Raízes de Plantas/metabolismo , Plantas Daninhas/efeitos dos fármacos , Plantas Daninhas/genética , Alinhamento de Sequência , Análise de Sequência de Proteína , Ácido Chiquímico/metabolismo , Glycine max , GlifosatoRESUMO
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.
Assuntos
Amaranthus/metabolismo , Glycine max/efeitos dos fármacos , Glicina/análogos & derivados , Herbicidas/metabolismo , Plantas Daninhas/metabolismo , 3-Fosfoshikimato 1-Carboxiviniltransferase/genética , 3-Fosfoshikimato 1-Carboxiviniltransferase/metabolismo , Amaranthus/efeitos dos fármacos , Argentina , Transporte Biológico , Glicina/metabolismo , Glicina/farmacologia , Resistência a Herbicidas , Herbicidas/farmacologia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Daninhas/efeitos dos fármacos , Glycine max/crescimento & desenvolvimento , GlifosatoRESUMO
The constant presence of genetically modified (GM) soybean in conventional seed lots has become a growing problem for international seed trade. In this context, seed companies have prompted the development of routine tests for accurate genetically modified soybean seeds detection. In this study, a quantitative PCR-based method was standardized in order to detect and quantify mixtures of seeds (i.e. certified seed) or GM grains (i.e. seeds came from field) into samples of non-GM soybean, in a way that soybean lots can be assessed within the standards established by legislation. The method involved the use of p35S-f2/petu-r1 primers targeting CP-4 enolpyruvylshikimate-3-phosphate synthase (cp4-epsps) gene (i.e. that confers herbicide tolerance in Roundup ReadyTM (RR)) for real-time PCR detection and quantification through mericon Quant GMO Detection Assay. The results revealed the method efficiency to detect and quantify the presence of even one soybean seed in batch used for routine evaluation of GM seeds. In addition, it was possible to detect of up to 0.1% of transgenic DNA relative to the soybean grains content. Thus, the sensitive GMO quantitative approach described in this study will provide support in supervising activities, and facilitate the process and control of GM soybean.
A constante presença da soja geneticamente modificada (GM) em lotes de sementes convencionais têm se tornado um grande problema para o comércio internacional de sementes. Neste contexto, as empresas de sementes estão em busca de testes de rotina extremamente precisos para a detecção de sementes de soja geneticamente modificadas. Neste estudo, um método baseado em PCR quantitativo foi padronizado para detectar e quantificar misturas de sementes (i.e. sementes certificadas) ou grãos geneticamente modificados (i.e. sementes oriundas do campo) dentro de lotes de soja não transgênica, de um modo que os lotes de soja possam ser avaliados dentro dos parâmetros estabelecidos pela legislação. O método envolveu o uso dos iniciadores p35S-f2/petu-r1 alvejando o gene CP-4 5-nolpiruvil-shikimato-3-fosfato sintase (cp4-epsps) (i.e. que confere a tolerância ao herbicida Roundup Ready® (RR)) para detecção e quantificação em PCR de tempo real via Ensaio de detecção Mericon Quant GMO. Os resultados revelaram um método eficiente para detectar e quantificar a presença de até mesmo uma única semente de soja no lote usado para a avaliação de rotina de sementes geneticamente modificadas. Adicionalmente, foi possível detectar até 0,1% de DNA transgênico relativo ao conteúdo de grãos de soja. Dessa forma, uma abordagem quantitativa sensível à soja geneticamente modificada foi descrita nesse estudo e poderá fornecer suporte em atividades de supervisão, além de facilitar o processo de controle da soja geneticamente modificada.