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Uruguayan agriculture has undergone dramatic changes in the last 50 years driven by the adoption of new agricultural production systems that incorporate zero tillage and herbicide resistant crops. This has resulted in a shift in weed species frequencies and the dispersion of introduced herbicide resistant weed populations. Finally, integrated weed management tools are being developed by research and extension services to manage herbicide-resistant (HR) weeds better and to reduce environmental impact of herbicides.

The study evaluated the effect of Carya illinoinensis plant extracts on lettuce seed germination and development. Experiment was carried out in a completely randomized experimental design with five treatments and replications. Plant extracts were prepared from the dry ground vegetable waste. The concentration was adjusted to 10% m.v-1. The treatments were classified into: heterogeneous pruning residues (HPR), leaves residues (LR), epicarp residues (ER), mesocarp residues (MR), and control treatment (CT, 100% water). The variables evaluated were: first germination count (GP4%), final germination count (GP7%), germination speed index (GSI), germination inhibition (PGI), frequency of abnormal seedlings (FAS), root length (RL), shoot length (SL), and total length of seedling (TLS). Extracts obtained from residues of C. illinoinensis decreased the lettuce seed germination, but their effect depends on the plant tissue (e.g. leaf, epicarp or mesocarp) used at production of plant extracts. Plant extracts from HPR and MR do not result in drastic allelochemical effects. Aqueous extracts from LR and ER reduced significantly the seed germination and the normal development of lettuce seedlings, with an absolute reduction in germination of 90.2% and 79.2%, respectively. Only plant extracts from leaf residues and epicarp residues from C. illinoinensis inhibit the germination and seedling development of L. sativa., O estudo avaliou o efeito de extratos de plantas de Carya illinoinensis na germinação e no desenvolvimento de sementes de alface. O experimento foi conduzido em delineamento inteiramente casualizado com cinco tratamentos e repetições. Extratos de plantas foram preparados a partir de resíduos vegetais secos. A concentração foi ajustada para 10% m.v-1. Os tratamentos foram classificados: resíduos de poda heterogêneos (HPR), resíduos de folhas (LR), resíduos de epicarpo (ER), resíduos de mesocarpo (MR) e tratamento de controle (CT, 100% água). As variáveis ​​avaliadas foram: primeira contagem de germinação (GP4%), contagem final de germinação (GP7%), índice de velocidade de germinação (GSI), inibição de germinação (PGI), frequência de plântulas anormais (FAS), comprimento de raiz (RL), comprimento de parte aérea (SL) e comprimento total da muda (TLS). Os extratos obtidos a partir dos resíduos de C. illinoinensis diminuem a germinação das sementes de alface, mas seu efeito depende do tecido vegetal (por exemplo, folha, epicarpo ou mesocarpo) utilizado na produção dos extratos vegetais. Os extratos vegetais de HPR e MR não resultam em efeitos alelopáticos drásticos. Os extratos aquosos de LR e ER reduziram significativamente a germinação das sementes e o desenvolvimento normal das plântulas de alface, com redução absoluta na germinação de 90,2% e 79,2%, respectivamente. Apenas extratos vegetais de resíduos de folhas e resíduos de epicarpo de C. illinoinensis inibem a germinação e o desenvolvimento de plântulas de L. sativa.

Chlorophylls and carotenoids are the main photosynthetic pigments in plants, and photosynthetic potential can be used to determine the nitrogen fixation or cycling capacity of cover crops. Therefore, this study quantified and compared the content of photosynthetic pigments in Raphanus sativus and Vicia sativa by using two different methods, namely the extraction method and measurements with a portable chlorophyll meter, and determined whether the results of these two methods showed a significant correlation. Photosynthetic pigments were measured, using both methods, in a greenhouse and laboratory, at four developmental stages: the vegetative stages I (30 days after sowing [DAS]), II (60DAS), and III (90DAS), and the reproductive stage (150DAS). The determination of the photosynthetic pigment content in R. sativus and V. sativa, obtained from the extraction method and chlorophyll index, revealed significant differences depending on the developmental stage in both species. Furthermore, the contents of chlorophyll a, chlorophyll b, and carotenoids determined using the extraction method showed high coefficients of correlation with the total chlorophyll index determined using the portable chlorophyll meter. Therefore, the portable chlorophyll meter can be used for the accurate evaluation of the photosynthetic potential of Raphanus sativus and Vicia sativa, which also saves time and reagents.

The study evaluated the germination performance of bean seeds (BRS Expedito) from different regions of southern Brazil submitted to different germination temperatures (20, 25 and 30º C). Were evaluated to germination (GER), first germination count (PCG), germination speed index (IVG), shoot dry mass (MSPA) and root dry mass (MSR). The seeds from São Mateus (PR) presented the highest average values for the variables GER, PCG and IVG in the three temperatures tested. The temperature increase (20 to 30 ºC) significantly influenced the dry biomass accumulation in the shoots and seedlings roots. The results indicate the existence of a phenotypic plasticity acquired by the cultivar due to local adaptation of the ecotypes., O estudo avaliou o desempenho germinativo de sementes de feijão (BRS Expedito) de diferentes regiões do sul do Brasil submetidas a diferentes temperaturas de germinação (20, 25 e 30º C). Foram avaliados: germinação (GER), primeira contagem de germinação (PCG), índice de velocidade de germinação (IVG), massa seca da parte aérea (MSPA) e massa seca da raiz (MSR). As sementes de São Mateus (PR) apresentaram os maiores valores médios para as variáveis GER, PCG e IVG nas três temperaturas testadas. O aumento da temperatura (20 a 30 ºC) influenciou significativamente o acúmulo de biomassa seca nas raízes e da parte area das platulas de feijão. Os resultados indicam a existência de uma plasticidade fenotípica adquirida pela cultivar devido à adaptação local dos ecótipos.

Weeds are host and multipliers of root-knot nematodes (Meloidogyne spp.). The status quo of the knowledge of the ability of Meloidogyne arenaria to reproduce in weeds is a little unknown. The present study aimed to evaluate the ability of M. arenaria to parasitize and reproduce in different weeds found in Brazil. Thirty-eight weed species were individually inoculated with 5000 eggs and second stage juveniles. Inoculated plants were kept in a greenhouse for 60 days. The design was completely randomized with twelve repetitions. The root system of each plant was evaluated for gall index, number of nematodes per root gram and reproduction factor. M. arenaria showed the ability to parasitize the 38 weed species. It was observed that 76.3% of the evaluated species were susceptible (RF ≥ 1.0) to M. arenaria. Oxalis corniculata resulted in the highest nematode RF (34.9). The present study identified for the first time the reproduction potential of M. arenaria on different weeds, showing their polyphagous habit, and indicating species of plants with greater ability to multiply this nematode that need more attention during the integrated management of this root-knot nematodes.

Meloidogyne ethiopica is considered to be one of the most economically important emerging nematode species, reported to cause crop losses to several hosts worldwide. The significance of this species is due to its high virulence and degree of polyphagia, in addition to persisting on weed hosts within agricultural fields. This study evaluated the host status of 36 different weed species, confirming the polyphagia habit of M. ethiopica and indicating which plant species may be alternative hosts for this plant nematode. Weed species were inoculated with 5000 eggs and second-stage juveniles (J2) of M. ethiopica, with gall index (GI), nematode/g root (Nem/g), and reproduction factor (RF) value determined following 60 days post inoculation. The data obtained indicate that many weed species may be excellent hosts for M. ethiopica. Plants deemed susceptible (RF ≥ 1.0) were: Acanthospermum australe, Amaranthus deflexus, A. hybridus, A. spinosus, A. viridis, Bidens pilosa, B. subalternans, Cardiospermum halicacabum, Commelina benghalensis, Cynodon dactylon, Euphorbia heterophylla, Galinsoga parviflora, Ipomoea grandifolia, I. nil, I. purpurea, Leonurus sibiricus, Nicandra physaloides, Oxalis corniculata, Portulaca oleracea, Raphanus raphanistrum, Sida rhombifolia, Solanum americanum, S. pseudocapsicum, S. sisymbriifolium, Sonchus oleraceus and Talinum paniculatum, representing 72.2% of the species assessed. The species Conyza bonariensis, Cyperus rotundus, Digitaria horizontalis, D. insularis, Echinochloa colonum, Eleusine indica, Lolium multiflorum, Polygonum hydropiperoides, Rhynchelytrum repens and Senecio brasiliensis were resistant to M. ethiopica (RF

A utilização indiscriminada de herbicidas na cultura do arroz tem provocado uma pressão de seleção de biótipos de arroz-vermelho resistentes aos herbicidas imidazolinonas. Diante disso, métodos alternativos de controle de plantas daninhas tornam-se uma alternativa para esta situação, tal como a busca de novos ingredientes ativos em compostos aleloquímicos de plantas. O trabalho foi realizado com objetivo de avaliar o potencial alelopático de diferentes concentrações do extrato aquoso de folhas de cultivares de arroz irrigado na germinação e no vigor de sementes de arroz-vermelho. O delineamento experimental adotado foi inteiramente casualizado, com quatro repetições, em esquema fatorial 4 x 5, onde: fator A - Extrato de folhas frescas das cultivares de arroz (BRS Querência, Irga 424, Roxinho e Cica 07) e fator B - Concentrações do extrato (0, 25, 50, 75 e 100%). Os extratos foram obtidos de folhas das plantas das cultivares em estádio reprodutivo R3 (saída da panícula). Estas foram trituradas em água destilada e posteriormente diluídas nas concentrações. Avaliaram-se a germinação, primeira contagem da germinação, índice de velocidade de germinação, comprimento da parte aérea e de raiz e massa seca da parte aérea e de raiz. De maneira geral, o efeito alelopático é maior nas cultivares desenvolvidas mais recentemente, sendo o extrato da cultivar IRGA 424, na concentração de 25%, o mais nocivo para o desempenho fisiológico de sementes de arroz-vermelho.

Chlorophylls and carotenoids are the main photosynthetic pigments in plants. The photosynthetic potential of crop plants is used to determine the correct rate of nitrogen fertilization. To date, no studies have been conducted to understand the relationship between different methods of measurement of photosynthetic pigments in oats. The objective of this study was to quantify and compare the levels of photosynthetic pigments in Avena strigosa and A. sativa using two different methods, the extraction method and portable chlorophyll meter, and to determine whether the results of these two methods showed a significant correlation. Photosynthetic pigments were measured using both methods in a greenhouse and the laboratory at four developmental stages: tillering [28 days after sowing (DAS)], vegetative stage I (55 DAS), vegetative stage II (75 DAS), and reproductive stage (120 DAS). The same leaves were used to measure the relative chlorophyll content using a portable chlorophyll meter and extractable chlorophyll using the laboratory extraction method. The readings of the chlorophyll index differed for each developmental stage of both A. sativa and A. strigosa. The contents of chlorophyll a, chlorophyll b, and carotenoids determined using the extraction method showed high coefficients of correlation with the total chlorophyll index determined using the portable chlorophyll meter. Thus, the measurement of chlorophyll using the portable chlorophyll meter can be used for the accurate evaluation of the photosynthetic potential of oats, thus saving time and reagents.

Weeds host of root-knot nematodes (Meloidogyne spp.), parasites of important crop plants mainly in tropical and subtropical regions, enable them to maintain themselves or increase their abundance in soils. To evaluate the host status of 31 weed species that commonly compete with crops, we experimentally inoculated them with 5000 eggs and second-stage juveniles (J2) of Meloidogyne enterolobii. Sixty days after inoculation, we measured several parameters related to infestation ability, including gall index (GI), number of eggs/g root, and reproduction factor (RF). About 77.4% (n = 24) of the weed species we assessed were susceptible (RF ≥ 1) to M. enterolobii infestation: Acanthospermum australe, Amaranthus deflexus, Amaranthus hybridus, Amaranthus spinosus, Amaranthus viridis, Bidens pilosa, Bidens subalternans, Cardiospermum halicacabum, Commelina benghalensis, Euphorbia heterophylla, Galinsoga parviflora, Ipomoea grandifolia, Ipomoea nil, Ipomoea purpurea, Leonurus sibiricus, Nicandra physaloides, Polygonum hydropiperoides, Portulaca oleracea, Rhynchelytrum repens, Sida rhombifolia, Solanum americanum, Solanum sisymbriifolium, Solanum pseudocapsicum, and Talinum paniculatum. In contrast, seven species were resistant (RF

Hairy fleabane (Conyza bonariensis L.) is a major weed of the conventional crop systems. Therefore, the objectives of the present study were to assess the responses of glyphosate-susceptible (S) and -resistant (R) C. bonariensis at various developmental stages and evaluate the physiological potential of seeds to propose alternative herbicides for the control of this weed. Two experiments were performed in replicates. The first experiment was performed in a greenhouse, arranged in a 2 × 3 × 10 factorial design. Specifically, two hairy fleabane biotypes (S and R) at different developmental stages (I, II, and III) were subjected to various treatments (glyphosate, chlorimuron-ethyl, metsulfuron-methyl, diclosulam, ammonium glufosinate, paraquat, paraquat+diuron, diquat, 2,4-D, and control). Percentage control was evaluated at 7, 14, 21, and 28 days after the application of the treatments (DAT), and shoot dry mass (SDM) was measured at 28 DAT. The second experiment was performed in a laboratory to evaluate the physiological potential of seeds based on the weight of 1000 seeds (TSW); shoot length (SL), radicle length (RL), total length (TL), fresh seedling mass (FSM), dry seedling mass (DSM), accelerated aging (AA) and cold test (CT), and germination (G) in response to cold and accelerated aging. The alternative herbicides tested effectively controlled biotype R up to the stage-I. Seeds of biotype R showed higher physiological potential in terms of all analyzed variables and exhibited greater tolerance to adverse conditions during seedling establishment. Therefore, strategies for the management of glyphosate-resistant hairy fleabane should aim at preventing new seed production. A buva (Conyza bonariensis L.) é umas das principais plantas daninhas dos sistemas de cultivos conservacionistas, especialmente por sua evolução à resistência ao herbicida glyphosate. Os objetivos deste trabalho foram verificar a resposta de Conyza bonariensis suscetível (S) e resistente (R) ao glyphosate em diferentes estádios a herbicidas alternativos e avaliar o potencial fisiológico de sementes destes biótipos. Dois estudos foram realizados e repetidos, sendo o primeiro em casa de vegetação em esquema fatorial 2x3x10, sendo A: biótipos de buva (S e R); B: estádios de desenvolvimento (I (1-2 folhas), II (5-6 folhas) e III (30-35 folhas)) e C: herbicidas (glyphosate, chlorimuron-etílico, metsulfuron-methyl, diclosulam, amônio-glufosinato, paraquat, paraquat+diuron, diquat, 2,4-D além de testemunha não aplicada).O segundo estudo foi desenvolvido em laboratório, realizando-se avaliações do potencial fisiológico das sementes, a partir do por peso de mil sementes (PMS), germinação (G), primeira contagem da germinação (PG), índice de velocidade de germinação (IVG) e emergência (IVE), comprimento da parte aérea (CPA), raiz (CR) e total (CT), matéria seca da parte aérea (MSPA), raízes (MSR) e total (MST), testes de frio e envelhecimento acelerado. O biótipo CR foi eficientemente controlado pelos herbicidas alternativos ao glyphosate, utilizados até o estádio de 6 folhas. As sementes do biótipo CR apresentaram desempenho fisiológico superior em todas as variáveis analisadas, com maior tolerância a condições adversas em seu estabelecimento. O manejo de buva resistente a glyphosate demanda a utilização de estratégias que visem evitar a produção de novas sementes.

Herbicide resistance is frequently reported in E. crus-galli globally with target and non-target site resistance mechanism to acetolactate synthase (ALS)-inhibiting herbicides. However, resistance to certain herbicides can result in increased sensitivity to other herbicides, a phenomenon called negative cross-resistance. The objective of this study is to identify the occurrence of negative cross-resistance (NCR) to the pro-herbicide clomazone in populations of E. crus-galli resistant to ALS inhibitors due to increased metabolization. Clomazone dose-response curves, with and without malathion, were performed in imazethapyr-resistant and -susceptible E. crus-galli biotypes. CYPs genes expression and antioxidant enzymes activity were also evaluated. The effective dose to reduce 50% (ED50) of dry shoot weight obtained in the clomazone dose-response curves of the metabolic based imazethapyr-resistant and -susceptible biotypes groups were 22.712 and 58.745 g ha−1, respectively, resulting in a resistance factor (RF) of 0.37, indicating the occurrence of NCR. The application of malathion prior to clomazone increased the resistance factor from 0.60 to 1.05, which indicate the reversion of the NCR. Some CYP genes evaluated were expressed in a higher level, ranging from 2.6–9.1 times according to the biotype and the gene, in the imazethapyr-resistant than in -susceptible biotypes following clomazone application. Antioxidant enzyme activity was not associated with NCR. This study is the first report of NCR directly related to the mechanism of resistance increased metabolization in plants. The occurrence of NCR to clomazone in E. crus-galli can help delay the evolution of herbicide resistance.

Soybean crop productivity is limited by several biotic factors, particularly plant-parasitic nematodes. Several species have been reported to cause crop damage, especially those of the genus Meloidogyne. Therefore, the aim of this study was to evaluate, the reaction of 28 soybean genotypes to Meloidogyne arenaria and M. morocciensis in a greenhouse. The soybean genotypes were the same for experiments with different species of plant-parasitic nematodes and were individually inoculated with 5,000 eggs + second-stage juveniles (J2) of Meloidogyne and kept in a greenhouse. After 60 days of inoculation, the roots of each plant were assessed for the number of galls, final population, and reproduction factor (RF = final population/initial population). The averages of the different variables were then compared to each other by the Scott-Knott cluster analysis at a significance level of 5%. All of the soybean genotypes in the study were susceptible to both nematodes, with RF ranging from 3.5 to 24.1 for M. arenaria and 5.3 to 37.5 for M. morocciensis.

Weeds can be hosting and alternative multipliers of root-knot nematodes (Meloidogyne spp.). Among the main weeds, species of the genus Ipomoea stands out for their cosmopolitan presence and the negative impact on crops. In addition, they can behave as hosts and promote the reproduction of pests, diseases, and nematodes. However, the ability of Meloidogyne nematodes to infect morning-glory (Ipomoea spp.) is little understood. In this context, the objective was to evaluate the reproduction of M. arenaria, M. enterolobii, M. ethiopica, M. hapla, M. incognita, M. javanica, M. luci, and M. morocciensis in I. grandifolia, I. hederifolia, I. nil, I. purpurea, and I. quamoclit. Plants were individually inoculated with 5,000 eggs and second-stage juveniles and kept in a greenhouse for 60 days. The design was completely randomized with six repetitions. After this period, the root system of each plant was evaluated to gall index (IG) and reproduction factor (RF). It was verified that the eight species of Melodoigyne have the capacity to parasitize I. grandifolia, I. hederifolia, I. nil, I. purpurea, and I. quamoclit, showing the susceptibility of these weeds to the plant-parasitic nematodes. The highest RF were observed for M. enterolobii with values of 12.5 and 12.9 for I. quamoclit and I. hederifolia, respectively. While M. arenaria obtained the lowest values, with RF ≤ 4.0 for all species of Ipomoea. Thus, weed species of the Ipomoea genus are potential hosts and multipliers of root-knot nematodes, making it important to be considered in integrated management strategies for these plant-parasitic nematodes.

Flooding is an important strategy for weed control in paddy rice fields. However, terrestrial weeds had evolved mechanisms of tolerance to flooding, resulting in new ‘snorkeling’ ecotypes. The aim of this review is to discuss the mechanisms of flooding tolerance in cultivated and weedy rice at different plant stages and the putative utility of this trait for weed management. Knowledge about flooding tolerance is derived primarily from crop models, mainly rice. The rice model informs us about the possible flooding tolerance mechanisms in weedy rice, Echinochloa species, and other weeds. During germination, the gene related to carbohydrate mobilization and energy intake (RAmy3D), and genes involved in metabolism maintenance under anoxia (ADH, PDC, and OsB12D1) are the most important for flooding tolerance. Flooding tolerance during emergence involved responses promoted by ethylene and induction of RAmy3D, ADH, PDC, and OsB12D1. Plant species tolerant to complete submersion also employ escape strategies or the ability to become quiescent during the submergence period. In weedy rice, the expression of PDC1, SUS3, and SUB1 genes is not directly related to flooding tolerance, contrary to what was learned in cultivated rice. Mitigation of flooding tolerance in weeds could be achieved with biotechnological approaches and genetic manipulation of flood tolerance genes through RNAi and transposons, providing a potential new tool for weed management.

Background: The use of pre-emergent herbicides is an important tool to control weeds, however the tolerance of soybean to these herbicides can vary according to the type of soil. Objective: The aim of this study was to evaluate sulfentrazone and diclosulam soybean selectivity in a sandy soil, in order to establish these herbicides as supporting tools in weed control. Methods: The treatments consisted of six doses of sulfentrazone (150 to 400 g ha-1) and diclosulam (25.2 to 75.6 g ha-1), and an untreated control. A field study was repeated in two growing seasons (2013/14 and 2014/15) in a sandy soil. Results: The occurrence of injury depended on the growing season. The first season presented lower rainfall rates during the crop cycle. The recommended dose of sulfentrazone (200 g ha-1) caused 26% and 10% of plant injury at 15 days after the treatment for the first and second season, respectively. For diclosulam, the recommended dose of 35.3 g ha-1 caused 20% and 8% of plant injury, respectively, for the first and second season. However, at the recommended doses, only for diclosulam and in the rainy season there was a reduction in soybean productivity. Conclusions: The herbicide sulfentrazone, although causing visual soybean plant injury, present satisfactory selectivity at recommended doses and can be used as an important tool on weed control on sandy soils. Similar response was observed for diclosulam in 2013/14. However, in a rainfall season diclosulam impacted on soybean yield at the recommended dose for sandy soils, with selectivity depending of the growth season.

Medicinal plants Scoparia dulcis showing symptoms caused by root-knot nematodes were detected in the municipality of Cachoeira do Sul, Rio Grande do Sul State, Brazil. Based on the morphological, esterase phenotypes, and molecular analyses of the mitochondrial DNA region between the cytochome oxidase subunit II and 16S rRNA genes (mtDNA) and species-specific sequence characterized amplified region (SCAR), the causal agent of the observed symptoms was identified as Meloidogyne javanica. Pathogenicity was confirmed by fulfilling a modified version of Koch’s postulates. To our knowledge, this is the first report of M. javanica infecting S. dulcis in Brazil.

Amaranthus palmeri plants showing symptoms caused by root-knot nematode infection were detected in the municipality of Palmita, Soriano, Uruguay. Based on morphology, esterase phenotypes, and species-specific sequence-characterized amplified region (SCAR) sequences, the causal agent was identified as Meloidogyne incognita. Pathogenicity was confirmed using a modified version of Koch's postulates. To our knowledge, this is the first report of M. incognita infecting the roots of the weed A. palmeri in Uruguay.

Samples of melon plants with aerial symptoms that represented yellowing of leaves and stunting, and below-ground galls on the roots from two growing areas in the Municipality of Vicente Dutra, Rio Grande do Sul State, Brazil, were obtained. The parasitizing nematode species was identified as Meloidogyne ethiopica based on perineal pattern morphology, esterase phenotypes, and molecular composition (D2–D3 region). This is the first formal record of melon being infected by M. ethiopica in Brazil.

Glyphosate is the herbicide most used worldwide. In cropping systems that rely on repeated applications of glyphosate or cultivate genetically modified soyabean crop, there are numerous cases of glyphosate resistant weeds, including Conyza bonariensis. Differences among competitive ability of Conyza spp. have been found. However, little information is available on the fitness costs related to glyphosate resistance in Conyza bonariensis. We evaluated growth, phenology, and seed viability of glyphosate-resistant (GR) and glyphosate-susceptible (GS) Conyza bonariensis from Brazil, in 2012 (fall/winter) and 2013 (spring/summer). When grown alone, in pots, C. bonariensis GR biotype developed more rapidly than the GS biotype, as evidenced by their earlier bolting, flowering, and seed set. In 2012, GR biotype showed 221.9 cm of plant height compared to 181.1 cm from GS, at the flowering time. In both years, the seed production per plant was superior for GR biotype, showing germination higher than 80% against 66.5% from the GS biotype. Thus, C. bonariensis GR biotype confirmed no fitness penalty also showing characteristics that allow us to infer in superior competitive with the absence of the herbicide. It is important to point out that the biotypes evaluated here have different genetic background and the differences between them may not be fully attributed to the resistance to glyphosate. However, the GR biotype can persist in the environment and outcompete with GS biotypes regardless of further glyphosate selection of pressure.

Cyperus rotundus plants showing symptoms of root knot were observed in the municipality of Santa Maria, Rio Grande do Sul state, Brazil. Based on the morphological, esterase phenotypes and molecular analyses of rDNA-ITS and D2-D3 regions of 28S rDNA, the causal agents of the observed symptoms were identified as Meloidogyne graminicola, pathogenicity was confirmed by fulfilling Koch’s postulates. To our knowledge, this is the first report of M. graminicola in C. rotundus in Rio Grande do Sul State, Brazil.

Juncus microcephalus plants showing symptoms of root-knot nematode infestation were observed in the municipality of Agudo, Rio Grande do Sul state, Brazil. Based on morphological observation, esterase phenotypes, and molecular analyses of rDNA-ITS and D2-D3 regions of 28S rDNA, the causal agent of the observed symptoms was identified as Meloidogyne graminicola. Pathogenicity of M. graminicola was confirmed by fulfilling modified Koch’s postulates. To our knowledge, this is the first report of M. graminicola in J. microcephalus in Rio Grande do Sul State, Brazil.

The resistance of weeds to herbicides is a consequence of one or more mechanisms in the plant, responsible for not allowing the herbicide to act properly at the active site. The objective of this study was to investigate the mechanism(s) of resistance to glyphosate in Conyza bonariensis. An experiment was conducted in November and December, 2012 and repeated in February and March, 2013 using a factorial arrangement of the treatments, where the factor A corresponded to biotypes of hairy fleabane, susceptible (S) and resistant (R); the factor B to seven rates of glyphosate from 0 to 11,520 g e.a. ha-1, and factor C were simulated environmental conditions of winter (12/8 oC day/night of temperature and 10/14 h of photoperiod) and summer (28/20 oC day/night of temperature and 14/10 h of photoperiod). An assay evaluating the shikimic acid was performed twice in the month of July 2013, with treatments arranged in a factorial arrangement, being factor A biotypes of hairy fleabane, S and R and the factor B seven glyphosate rates (0 to 28,8 mg a.e. L-1). The R biotype of C. bonariensis does not appear to present the sequestration of herbicide in the vacuole as the mechanism of resistance. However, the low accumulation of shikimate by the R biotype characterizes lower sensitivity of EPSPs enzyme to glyphosate, inferring that this is the present mechanism of resistance in plants of C. bonariensis. However, the resistance cannot be associated to a unique mechanism of resistance, requiring further studies to its understanding. RESUMO A resistência de plantas daninhas aos herbicidas é consequência da ocorrência de um ou mais mecanismos na planta, responsáveis por não deixarem o herbicida atuar de forma eficiente sobre o local de ação. O objetivo deste estudo foi investigar o(s) mecanismo(s) de resistência em Conyza bonariensis ao herbicida glyphosate. Um experimento foi conduzido de novembro a dezembro de 2012 e repetido em fevereiro e março de 2013, com arranjo fatorial, em que o fator A correspondeu aos biótipos de buva suscetível (S) e resistente (R); o fator B, a sete doses de glyphosate, que variaram de 0 a 11.520 g e.a. ha-1; e o fator C às condições que simularam o inverno (temperatura de 12/8 oC dia/noite e fotoperíodo de 10/14 horas) e verão (temperatura de 28/20 oC dia/noite e fotoperíodo de 14/10 horas). Um ensaio que avaliou o acúmulo de shiquimato foi realizado duas vezes no mês de julho de 2013, com tratamentos dispostos em esquema fatorial, sendo o fator A os biótipos de buva, S e R, e o fator B, sete doses de glyphosate (0 a 28,8 mg e.a. L-1). O biótipo R de C. bonariensis aparenta não apresentar o mecanismo de sequestro do herbicida no vacúolo como mecanismo de resistência. Entretanto, o menor acúmulo de shiquimato pelas plantas do biótipo R caracteriza a menor sensibilidade da enzima EPSPS ao glyphosate, inferindo que esse seja o mecanismo de resistência presente em plantas de C. bonariensis. Contudo, a resistência pode não estar atrelada a apenas um mecanismo de resistência, exigindo, para seu inteiro entendimento, estudos complementares.

RESUMO A aveia-branca (Avena sativa) é uma importante alternativa para cultivos de inverno no sul do Brasil. Contudo, elevados percentuais de acamamento limitam sua produtividade. Nesse contexto, a utilização de reguladores de crescimento pode ser uma opção para evitar o acamamento e obter maior produtividade. O objetivo deste trabalho foi avaliar o efeito de doses do regulador de crescimento trinexapac-ethyl sobre as características agronômicas da aveia-branca, bem como sua influência na qualidade fisiológica e sanitária das sementes. Um experimento foi conduzido em campo, onde foi avaliada a influência de quatro doses de trinexapac-ethyl (0, 50, 100 e 150 g i.a. ha-1) sobre a estatura de planta, o diâmetro de colmo, o percentual de acamamento e os componentes do rendimento. Um segundo experimento foi conduzido em laboratório, onde sementes provenientes do estudo em campo foram avaliadas quanto a qualidade fisiológica a partir da mensuração da germinação, primeira contagem da germinação, condutividade elétrica, comprimento e massa de plântulas, envelhecimento acelerado, teste de frio, índice de velocidade de germinação, índice de velocidade de emergência, massa seca de plântulas em campo e sanidade pelo método de Blotter Test. A utilização de doses crescentes de trinexapac-ethyl reduziu de forma quadrática a estatura, bem como o acamamento de plantas de aveia-branca. A dose de 100 g i.a ha-1 de regulador de crescimento proporcionou os melhores resultados para os componentes de produtividade em A. sativa. O uso do trinexapac-ethyl afeta negativamente a germinação e o vigor de sementes de aveiabranca, assim como a sua sanidade, reduzindo a capacidade de estabelecimento e desenvolvimento inicial da cultura.

Weeds can be hosts of root-lesion nematode (Pratylenchus spp.), maintaining or increasing their population in the soil. The objective of this study was to evaluate the reaction of 25 weeds species to the nematode Pratylenchus zeae. The weed plants were individually inoculated with 1,000 individuals of P. zeae and maintained in a greenhouse for 90 days. After this period, eggs and nematodes were extracted, quantified, and the reproduction factor (RF = final population/initial population) was calculated. All tested weeds were susceptible (RF>1) to P. zeae, and the species Brachiaria decumbens, Rhynchelytrum repens, Digitaria insularis, D. horizontalis, B. brizantha were the most susceptible to this parasite. RESUMO As plantas daninhas podem ser hospedeiras de nematoides das lesões (Pratylenchus spp.), mantendo ou elevando sua população no solo. O objetivo deste trabalho foi avaliar a reação de 25 espécies de plantas daninhas a Pratylenchus zeae. As plantas daninhas foram individualmente inoculadas com 1.000 espécimes de P. zeae e mantidas em casa de vegetação por 90 dias. Após esse período, os ovos e nematoides foram extraídos e quantificados, sendo calculado o fator de reprodução (FR = população final/população inicial). Todas as plantas daninhas avaliadas comportaram-se como suscetíveis (FR>1) para P. zeae, sendo as espécies Brachiaria decumbens, Rhynchelytrum repens, Digitaria insularis, D. horizontalis e B. brizantha as mais suscetíveis a esse parasita.

Chlorophylls and carotenoids are the main photosynthetic pigment in plants. In the weeds, the greatest amount of photosynthetic pigments can result in high competitiveness of the species. The aim of this study was to quantify the content of photosynthetic pigments in biotypes of fleabane (Conyza bonariensis) susceptible and resistant to glyphosate, by two different methods, as well as a correlation between chlorophyll content obtained by portable and classical methodology (extractable chlorophyll). An experiment was conducted in greenhouse and laboratory, 2 x 5 factorial scheme, where factor A was equivalent to biotypes of fleabane (resistant and susceptible to glyphosate) and factor B to developmental stages plants (rosette vegetative I, II and III and reproduction). At all stages of development, fleabane plants were evaluated with the portable determiner (chlorophyll content) and then the same leaves were subjected to classical methodology laboratory (extractable pigments). The resistant biotype of fleabane showed higher contents of chlorophyll a, b, and total carotenoids, inferring a greater competitive potential regarding the susceptible population to the herbicide. The portable determiner of chlorophyll showed high correlation with the classical method of determination of photosynthetic pigments, and can thus be used to accurately assess this, saving time and reagents. Clorofilas e carotenoides são os principais pigmentos fotossintéticos em plantas. Nas plantas daninhas, a maior quantidade de pigmentos fotossintéticos pode resultar em elevada competividade da espécie. O objetivo deste trabalho foi quantificar o teor de pigmentos fotossintéticos em biótipos de buva (Conyza bonariensis) suscetível e resistente ao herbicida glyphosate, por dois diferentes métodos, bem como estabelecer uma correlação entre o índice de clorofila obtido pelo equipamento portátil e a metodologia clássica (clorofila extraível). Um experimento foi conduzido em casa de vegetação e laboratório, em esquema fatorial 2 x 5, em que o fator A equivaleu aos biótipos de buva (resistente e suscetível a glyphosate) e o fator B, a estádios de desenvolvimento das plantas (roseta, vegetativo I, II e III, e reprodutivo). Em todos os estádios de desenvolvimento, as plantas de buva foram avaliadas com o determinador portatil (índice de clorofila); em seguida, as mesmas folhas foram submetidas à metodologia clássica de laboratório (pigmentos extraíveis). O biótipo de buva resistente apresentou maiores teores de clorofila a, b, total e carotenoides, demonstrando maior potencial competitivo frente ao biótipo suscetível ao herbicida glyphosate. O determinador portátil de clorofila apresentou alta correlação com o método clássico de determinação de pigmentos fotossintéticos, podendo, assim, ser usado com precisão na avaliação destes, proporcionando economia de tempo e reagentes.

The flooded environment brings about injuries to soybeans that vary depending on the adaptation ability of the genotype. Oxygen deprivation promotes the induction of the expression of genes related to glycolysis and fermentation pathways to maintain energy metabolism and, in addition to reducing-power consuming processes, act in the formation of adaptive structures and the maintenance of the redox status of the plant. The aim of this work was to evaluate the relative expression of genes related to soil flooding response in two contrasting soybean cultivars. Soybean plants of the sensitive (BRS 154) and tolerant (I27) cultivars at the V1 development stage were submitted to the flooding and control conditions (without flooding) for 0, 24, 48, and 96 hours. The relative expression of genes associated with flooding, including enolase (ENO), alcohol dehydrogenase 1 (ADH1), alanine aminotransferase 2 (ALAT2), hemoglobin 1 (GLB1), LOB41 domain-containing protein (LBD41), xyloglucan endotransglycosylase (XETP) and ascorbate peroxidase (APX2), was evaluated by means of RT-qPCR. The relative expression, in general, increased with flooding, especially in the root tissue. Cultivar I27 responded positively as observed by the expression of the maintenance genes of energy metabolism, structural changes and detoxification, suggesting the presence of three tolerance mechanisms in the flooding response.

A antecipação da colheita da soja é possível com uso da prática de dessecação pré-colheita, a qual reduz o tempo de permanência das sementes no campo, após a maturação fisiológica. O objetivo deste trabalho foi avaliar o efeito da época de aplicação do herbicida paraquat, como dessecante na pré-colheita da soja, sobre a produtividade e qualidade fisiológica de sementes. O trabalho constou de duas etapas: um experimento em campo, conduzido no município de Jaboticaba-RS, safra 2010/2011, e uma análise da qualidade fisiológica das sementes. Os tratamentos consistiram de três épocas de aplicação do paraquat (240 g i.a. ha‑1), R6, R7.1 e R7.3, bem como de um tratamento testemunha (sem dessecação). Foram avaliados a produtividade de grãos e os componentes da produtividade. A análise da qualidade das sementes foi conduzida no Laboratório de Produção e Tecnologia de Sementes da UFSM, Campus de Frederico Westphalen, RS, onde se realizaram os seguintes testes: germinação; primeira contagem de germinação, comprimento de parte aérea e radicular, matéria seca de plântulas, envelhecimento acelerado, condutividade elétrica, emergência em campo e índice de velocidade de emergência. A aplicação de paraquat como dessecante na pré‑colheita da soja, nos estádios R6 e R7.1, provoca queda acentuada na produtividade da cultura. A dessecação sem perda de potencial produtivo da soja só é viável a partir do estádio R7.3. Sementes oriundas de plantas com dessecação nos estádios R6 e R7.1 apresentam percentual superior e maior velocidade de germinação. Entretanto, sementes de plantas com dessecação no estádio R6 possuem menor vigor de plântulas.

The establishment of commercial crops in succession to winter cover crops that leaves a dense straw layer provides significantly suppression of weeds. The objective of this work was to evaluate the suppressive potential of winter cover crops on weed infestation in maize and its effect on the yield of the maize sown in succession. The experiment was conducted in the 2012/2013 crop season, in an area of the UFSM Campus Frederico Westphalen, State of Rio Grande do Sul. Four different species of cover crops (black oat, ryegrass, vetch and forage radish) were seeded and a fallow area was used as control. Evaluations to quantify the dry matter and chemical desiccation were performed at the full flowering period of the cover crops. Maize was sown in no-tillage system, in succession to the cover crops. The incidence and shoot dry matter of weeds (g 0.25 m-2) was evaluated 15 days after the maize emergence. The main weed species in the area were: morning-glory (Ipomoea grandifolia), wild poinsettia (Euphorbia heterophylla), large crabgrass (Digitaria sanguinalis) and purple nutsedge (Cyperus rotundus). In general, vetch and ryegrass were the winter cover crops that better suppressed the weeds evaluated. The best maize yield was found in the area previously covered with ryegrass, inferring a relation between the cover crop and suppression of weeds and crop yield. RESUMO O estabelecimento de culturas comerciais em sucessão a coberturas de inverno, com presença de densa camada de palha, proporciona significativa supressão de plantas daninhas. O objetivo deste trabalho foi avaliar o potencial supressor de coberturas de inverno sobre a incidência inicial de plantas daninhas na cultura do milho e seu efeito na produtividade da cultura semeada em sucessão. Um experimento foi conduzido no ano agrícola de 2012/2013, em área experimental da UFSM, Campus de Frederico Westphalen RS. Foram utilizadas quatro diferentes espécies de cobertura de inverno (aveia-preta, azevém, ervilhaca e nabo) semeadas em faixas, além da testemunha mantida em pousio. No pleno florescimento das coberturas foi realizada a quantificação da massa seca e a dessecação das mesmas. O milho foi semeado em sistema de plantio direto em sucessão às coberturas. Aos 15 dias após a emergência do milho foi avaliada a incidência e a massa seca de parte aérea das plantas daninhas presentes (0,25 m²). As principais espécies daninhas presentes na área foram: corriola (Ipomoea grandifolia), leiteiro (Euphorbia heterophylla), milhã (Digitaria sanguinalis), tiririca (Cyperus rotundus). De forma geral, a ervilhaca e o azevém foram as coberturas de inverno com maior capacidade supressora sobre as plantas daninhas avaliadas. O melhor desempenho produtivo do milho foi observado sobre a palhada de azévem, inferindo para uma relação de supressão de plantas daninhas e produtividade da cultura.