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Glyphosate Applied at the Early Reproductive Stage Impairs Seed Production of Glyphosate-Resistant Hairy Fleabane Translated title: Glyphosate Aplicado no Início do Estádio Reprodutivo Inviabiliza a Produção de Sementes de Buva Resistente ao Glyphosate

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      Abstract

      ABSTRACT: Glyphosate-resistant hairy fleabane [Conyza bonariensis (L.) Cronq.] is one of the most important weeds in the world. Among the factors that make this weed species widely distributed in the most diverse environments is the high seed production capacity and dispersal. Hairy fleabane plants not controlled by herbicide application regrowth and overcome crop canopy, use environmental resources, interfere with crops, and complete their life cycle by producing thousands of seeds and replenishing the seed bank. Management strategies that reduce production and viability of hairy fleabane seeds can be adopted within the integrated management to reduce the seed bank and prevent further infestations. In this way, experiments were carried out in a greenhouse and laboratory of seed analysis to evaluate the effect of glyphosate (1,480 g a.e. ha-1) on the production and viability of glyphosate-resistant hairy fleabane seeds when applied at the vegetative and reproductive stages. Seed production was reduced by 68.4 and 100% when glyphosate was applied on hairy fleabane plants at the vegetative and early reproductive stages, respectively, regarding to the control. The viability of hairy fleabane seeds was not influenced by treatments at the evaluated stages. However, glyphosate treatment reduced the hairy fleabane seed production when applied at the vegetative stage . Hairy fleabane seed production is not feasible when glyphosate is applied at the early reproductive stage.

      Translated abstract

      RESUMO: A buva [Conyza bonariensis (L.) Cronq.] resistente ao glyphosate é uma das principais plantas daninhas do mundo. Um dos fatores que fazem com que esta planta esteja amplamente distribuída nos mais diversos ambientes é sua alta capacidade de produção e dispersão de sementes. Plantas de buva não controladas pela aplicação de herbicidas rebrotam e sobressaem-se ao dossel da cultura, se beneficiam dos recursos do ambiente, interferem com as culturas, completam seu ciclo produzindo milhares de sementes e realimentando o banco de sementes. Estratégias de manejo que reduzam a produção e viabilidade de sementes de buva podem ser adotadas dentro do manejo integrado, a fim de o banco de sementes e prevenir futuras infestações. Foram realizados experimentos em casa de vegetação e em laboratório de análise de sementes com o objetivo de avaliar o efeito da aplicação de glyphosate nos estádios vegetativo e reprodutivo na produção e viabilidade de sementes de buva resistente ao glyphosate (1.480 g e.a. ha-1). Os resultados demonstram que a produção de sementes reduziu em 68,4% e 100% quando o glyphosate foi aplicado em plantas de buva nos estádios vegetativo e início do reprodutivo, respectivamente, em relação a plantas não tratadas. A viabilidade das sementes de buva não foi influenciada pelos tratamentos nos estádios avaliados. Entretanto, a aplicação do glyphosate no estádio vegetativo da buva reduz a produção de sementes. A produção de sementes de buva é inviabilizada quando o glyphosate é aplicado no início do estádio reprodutivo.

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      Characterization of the horseweed (Conyza canadensis) transcriptome using GS-FLX 454 pyrosequencing and its application for expression analysis of candidate non-target herbicide resistance genes.

      The de novo transcriptome sequencing of a weedy plant using GS-FLX 454 technologies is reported. Horseweed (Conyza canadensis L.) was the first broadleaf weed to evolve glyphosate resistance in agriculture, and also is the most widely distributed glyphosate-resistant weed in the United States and the world. However, available sequence data for this species are scant. The transcriptomic sequence should be useful for gene discovery, and to help elucidate the non-target-based glyphosate resistance mechanism and the genomic basis of weediness. Sequencing experiments yielded 411 962 raw reads, an average read length of 233 bp and a total dataset of 95.8 Mb (NCBI accession number SRA010952). After trimming and quality control, 379 152 high-quality sequences were retained and assembled into contigs. The assembly resulted in 31 783 unique transcripts, including 16 102 contigs and 15 681 singletons. The average coverage depth for each contig and each nucleotide position was 22-fold and 12-fold respectively. A total of 16 306 unique sequences were annotated by searching a custom plant protein database. The utility of the transcriptome data was demonstrated by further exploration of ABC transporters, which were previously hypothesized to play a role in non-target glyphosate resistance. Real-time RT-PCR primers were designed from the transcriptome data, which made it possible to assess expression patterns of 17 ABC transporters from resistant and susceptible horseweed accessions from Tennessee, with and without glyphosate treatment. These results show that GS-FLX 454 sequencing is a powerful and cost-effective platform for the development of functional genomic tools for a weed species.
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        Factors affecting germination of horseweed (Conyza canadensis)

        The influence of environmental factors on germination and emergence of horseweed was examined in growth chamber experiments. Germination was highest (61%) under 24/20 C day/night temperature under light. Horseweed seed germination was observed under both light (13 h photoperiod) and complete darkness (24 h), but germination under continuous darkness was only 0 to 15% compared with 0 to 61% under light. All other experiments were conducted under 24/20 C and 13-h light conditions. Germination was 19 to 36% over a pH range from 4 to 10, with a trend toward higher germination under neutral-to-alkaline conditions. Horseweed germination was > 20% at < 40 mM NaCl concentration and lowest (4%) at 160 mM NaCl. These data suggest that even at high soil salinity conditions, horseweed can germinate. Germination of horseweed decreased from 25% to 2% as osmotic potential increased from 0 (distilled water) to −0.8 MPa, indicating that germination can still occur under moderate water stress conditions. Horseweed seedling emergence was at its maximum on the soil surface, and no seedlings emerged from seeds placed at a depth of 0.5 cm or higher.
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          Permanent Genetic Resources added to Molecular Ecology Resources database 1 January 2009-30 April 2009.

          This article documents the addition of 283 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Agalinis acuta; Ambrosia artemisiifolia; Berula erecta; Casuarius casuarius; Cercospora zeae-maydis; Chorthippus parallelus; Conyza canadensis; Cotesia sesamiae; Epinephelus acanthistius; Ficedula hypoleuca; Grindelia hirsutula; Guadua angustifolia; Leucadendron rubrum; Maritrema novaezealandensis; Meretrix meretrix; Nilaparvata lugens; Oxyeleotris marmoratus; Phoxinus neogaeus; Pristomyrmex punctatus; Pseudobagrus brevicorpus; Seiridium cardinale; Stenopsyche marmorata; Tetranychus evansi and Xerus inauris. These loci were cross-tested on the following species: Agalinis decemloba; Agalinis tenella; Agalinis obtusifolia; Agalinis setacea; Agalinis skinneriana; Cercospora zeina; Cercospora kikuchii; Cercospora sorghi; Mycosphaerella graminicola; Setosphaeria turcica; Magnaporthe oryzae; Cotesia flavipes; Cotesia marginiventris; Grindelia Xpaludosa; Grindelia chiloensis; Grindelia fastigiata; Grindelia lanceolata; Grindelia squarrosa; Leucadendron coniferum; Leucadendron salicifolium; Leucadendron tinctum; Leucadendron meridianum; Laodelphax striatellus; Sogatella furcifera; Phoxinus eos; Phoxinus rigidus; Phoxinus brevispinosus; Phoxinus bicolor; Tetranychus urticae; Tetranychus turkestani; Tetranychus ludeni; Tetranychus neocaledonicus; Tetranychus amicus; Amphitetranychus viennensis; Eotetranychus rubiphilus; Eotetranychus tiliarium; Oligonychus perseae; Panonychus citri; Bryobia rubrioculus; Schizonobia bundi; Petrobia harti; Xerus princeps; Spermophilus tridecemlineatus and Sciurus carolinensis. © 2009 Blackwell Publishing Ltd.
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            Author and article information

            Affiliations
            Pelotas Rio Grande do Sul orgnameUniversidade Federal de Pelotas Brazil
            Passo Fundo Rio Grande do Sul orgnameEmbrapa Trigo Brazil
            Contributors
            Role: ND
            Role: ND
            Role: ND
            Role: ND
            Role: ND
            Role: ND
            Journal
            pd
            Planta Daninha
            Planta daninha
            Sociedade Brasileira da Ciência das Plantas Daninhas (Viçosa, MG, Brazil )
            0100-8358
            1806-9681
            2019
            : 37
            S0100-83582019000100198 10.1590/s0100-83582019370100104

            This work is licensed under a Creative Commons Attribution 4.0 International License.

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            Product Information: SciELO Brazil
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