Aspectos ecofisiológicos da germinação de sementes em biótipos de Sagittaria montevidensis resistentes e suscetível a herbicidas

The objective of this work was to evaluate the ecophysiological aspects of seed germination in California arrowhead (Sagittaria montevidensis) biotypes resistant and susceptible to herbicides. The experimental design was completely randomized. In paddy rice fields, seeds were collected from two biotypes that are resistant (SAGMO 10 and SAGMO 32) and from one that is susceptible (SAGMO 35) to acetolactate synthase and photosystem II inhibiting herbicides. Seed dormancy release was performed with 2.0% potassium nitrate, chemical (1.0% H2SO4 for 30 s) and mechanical (sandpaper) scarification, 10 ppm gibberellic acid, water imbibition for 24 hours, water bath at 60°C, and a control. Germination was evaluated at temperatures from 10 to 40°C and seedling emergence at 0.0, 0.5, 1.0, 2.0, 4.0, and 5.0 cm burial depths. All biotypes showed a germination higher than 70% after mechanical scarification. The highest germination rate occurs at 25.9°C for SAGMO 35, the susceptible biotype, and at 26.2 and 26.5°C, respectively, for SAGMO 10 and SAGMO 32, the resistant biotypes. For all biotypes, the highest seedling emergence occurs in seeds positioned at the 0.5 and 1.0 cm burial depths.O objetivo deste trabalho foi avaliar aspectos ecofisiológicos da germinação de sementes em biótipos de sagitária (Sagittaria montevidensis) resistentes e suscetível a herbicidas. O delineamento experimental foi o inteiramente casualizado. Em campos de arroz, foram colhidas sementes de dois biótipos resistentes (SAGMO 10 e SAGMO 32) e de um suscetível (SAGMO 35) aos herbicidas inibidores da acetolactato sintase e do fotossistema II. A liberação da dormência foi realizada com 2,0% de nitrato de potássio, escarificação química (1,0% de H2SO4 por 30 s) e mecânica (lixa), 10 ppm de ácido giberélico, embebição em água por 24 horas, banho-maria a 60oC e um controle. Avaliaram-se a germinação às temperaturas de 10 a 40°C e a emergência de plântulas aos 0,0, 0,5, 1,0, 2,0, 4,0 e 5,0 cm de profundidade de enterrio. Todos os biótipos apresentaram germinação superior a 70% após escarificação mecânica. A maior taxa de germinação ocorre a 25,9°C para SAGMO 35, o biótipo suscetível, e a 26,2 e 26,5°C, respectivamente, para SAGMO 10 e SAGMO 32, biótipos resistentes. Para todos os biótipos, a maior emergência de plântulas ocorre em sementes posicionadas a 0,5 e 1,0 cm de profundidade de enterrio

Fitness costs of susceptible and resistant radish biotypes to ALS-inhibitor herbicides

Radish is an important weed that causes yield reduction in winter crops in southern Brazil. The control chemical of radish is an important and essential step to prevent damage on crops. However the intensive use of ALS-inhibitors herbicides favors the selection resistant biotypes. The selection can influence the adaptive traits of biotypes with physiological changes and growth variables and plant reproduction. The objective of the study was compare the fitness costs of susceptible and resistant radish biotypes to ALS-inhibitors herbicides. The experiment was conducted in greenhouse using completely randomized design with five replications. The treatments were arranged in factorial arrangement corresponding to susceptible and resistant biotypes (B1 and B4) and nine sampling times (14, 28, 42, 56, 70, 84, 98, 112 and 126 days after emergency), respectively. The variables evaluated were plant height, shoot dry matter, root dry matter, total dry matter, leaf area, growth rate, relative growth rate, leaf area ratio, number of siliques and seeds produced per plant. The results showed that the resistant biotype (B4) had no fitness costs when compared to the susceptible biotype (B1).Radish is an important weed that causes yield reduction in winter crops in southern Brazil. The control chemical of radish is an important and essential step to prevent damage on crops. However the intensive use of ALS-inhibitors herbicides favors the selection resistant biotypes. The selection can influence the adaptive traits of biotypes with physiological changes and growth variables and plant reproduction. The objective of the study was compare the fitness costs of susceptible and resistant radish biotypes to ALS-inhibitors herbicides. The experiment was conducted in greenhouse using completely randomized design with five replications. The treatments were arranged in factorial arrangement corresponding to susceptible and resistant biotypes (B1 and B4) and nine sampling times (14, 28, 42, 56, 70, 84, 98, 112 and 126 days after emergency), respectively. The variables evaluated were plant height, shoot dry matter, root dry matter, total dry matter, leaf area, growth rate, relative growth rate, leaf area ratio, number of siliques and seeds produced per plant. The results showed that the resistant biotype (B4) had no fitness costs when compared to the susceptible biotype (B1)

Interference of volunteer corn on soybean cultivars growth and yield

Spontaneous corn plants in soybean crop are considered weeds because they compete for the same environmental resources. The objective of this study was to evaluate the competitive ability of soybean cultivars when in coexistence with spontaneous corn plants. A field experiment was conducted in CCGLTEC, Cruz Alta/RS, in 2014/15, in a split-plot design, with the main plot being composed of four different cultivars (CD 2694, BMX 7166, TEC 5718, TEC 6029) and the subplots of interference conditions (without the presence of corn volunteer plants, in the presence of corn until the V3, V6, V9 stages, or for the entire soybean cycle. Leaf area, shoot dry mass, plant height, chlorophyll index, and development stage were determined at 15, 30, and 49 DAE; we also determined apparent biological productivity, apparent harvest index, and components of productivity and grain yield. The cultivars showed losses in leaf area and shoot dry mass when in coexistence with corn (8 plants m-2) in the three periods evaluated. All cultivars showed losses in apparent biological productivity, apparent harvest index, and final grain yield when growing under competition throughout the cycle. Cultivars with a medium/long growth cycle, such as CD 2694 (maturity groups (GM): 6.9) and BMX 7166 (GM: 6.6), show a higher competitive ability up to V9 stage in contrast to cultivars with a short cycle, such as TEC 5718 (GM: 5.9) and TEC 6029 (GM: 5.7).Spontaneous corn plants in soybean crop are considered weeds because they compete for the same environmental resources. The objective of this study was to evaluate the competitive ability of soybean cultivars when in coexistence with spontaneous corn plants. A field experiment was conducted in CCGLTEC, Cruz Alta/RS, in 2014/15, in a split-plot design, with the main plot being composed of four different cultivars (CD 2694, BMX 7166, TEC 5718, TEC 6029) and the subplots of interference conditions (without the presence of corn volunteer plants, in the presence of corn until the V3, V6, V9 stages, or for the entire soybean cycle. Leaf area, shoot dry mass, plant height, chlorophyll index, and development stage were determined at 15, 30, and 49 DAE; we also determined apparent biological productivity, apparent harvest index, and components of productivity and grain yield. The cultivars showed losses in leaf area and shoot dry mass when in coexistence with corn (8 plants m-2) in the three periods evaluated. All cultivars showed losses in apparent biological productivity, apparent harvest index, and final grain yield when growing under competition throughout the cycle. Cultivars with a medium/long growth cycle, such as CD 2694 (maturity groups (GM): 6.9) and BMX 7166 (GM: 6.6), show a higher competitive ability up to V9 stage in contrast to cultivars with a short cycle, such as TEC 5718 (GM: 5.9) and TEC 6029 (GM: 5.7)

PROPAGAÇÃO IN VITRO DE Casearia sylvestris SWARTZ (SALICACEAE)

In order to do an in vitro propagation of Casearia sylvestris, a tree native to Brazilian forests, studies of in vitro seed germination were performed and aseptic seedlings obtained were used as explant donors for micropropagation. Mature and immature seeds, stored for 10 days at 10 or 25°C were inoculated in medium containing 10% of MS salts and kept in the light (a 16-hour photoperiod) or continuous dark, at 25°C. For immature seeds, gibberellic acid (GA3) was or was not tested at a concentration of 1.5 mg l-1. From the seedlings obtained, the cotyledon and apical segments were removed and cultured in complete MS medium with five combinations of 6-benzylaminopurine (BAP) and naphthalene acetic acid (NAA): 0.0; 0.25; 0.5; 1.0; 2.0 and 0.0; 0025; 0.05; 0.1; 0.2 mg L-1, respectively. The aerial shoots formed in vitro were cultured in MS medium containing 0.0 or 1.5 mg L-1 indole-3-butyric acid (IBA) for rooting. The highest percentage of germination (60%) occurred in mature seeds exposed to light, regardless of other treatments, and may be considered positive photoblastic. The highest percentage of germination of immature seeds (27%) occurred when previously stored at 10 ° C with or without GA3. The induction of aerial shoots was more efficient in apical segments in a medium containing the lowest combination of BAP and NAA or free of these growth regulators. The higher number of roots occurred in aerial shoots obtained from cotyledon segments, with or without IBA. After acclimatization, 83% of the plants survived.Com o objetivo obter a propagação in vitro de Casearia sylvestris, árvore nativa das florestas brasileiras, estudos de germinação in vitro das sementes foram realizados e as plântulas assépticas obtidas foram usadas como doadoras de explantes na micropropagação. Sementes maduras e imaturas, armazenadas por 10 dias a 10 ou 25°C foram inoculadas em meio contendo 10% de sais de MS e mantidas na luz (fotoperíodo de 16 horas) ou escuro contínuo, a 25°C. Para sementes imaturas, testou-se ou não ácido giberélico (GA3) na concentração de 1,5 mg l-1. Das plântulas obtidas, segmentos cotiledonares e apicais foram retirados e cultivados em meio MS completo com cinco combinações de 6-benzilaminopurina (BAP) e ácido naftalenoacético (ANA): 0,0; 0,25; 0,5; 1,0; 2,0 e 0,0; 0025; 0,05; 0,1; 0,2 mg L-1, respectivamente. As brotações aéreas formadas in vitro foram cultivadas em meio MS contendo 0,0 ou 1,5 mg L-1 de ácido indol-3-butírico (IBA) para o enraizamento. O maior percentual de germinação (60%) ocorreu em sementes maduras expostas à luz, independentemente dos demais tratamentos, podendo ser consideradas fotoblásticas positivas. A maior percentagem de germinação das sementes imaturas (27%) ocorreu quando previamente armazenadas a 10°C, com ou sem GA3. A indução de brotos aéreos foi mais eficiente em segmentos apicais e em meio contendo a menor combinação de BAP e ANA ou isento destes reguladores de crescimento. O maior número de raízes ocorreu em brotos obtidos a partir de segmentos cotiledonares, com ou sem AIB. Após a aclimatização, 83% das plantas sobreviveram

Burial depths favor Italian ryegrass persistence in the soil seed bank.

ABSTRACT: Italian ryegrass (Lolium multiflorum Lam.) is a weed broadly found in fields cultivated with wheat and barley crops. Seed inputs into the soil before harvesting winter crops increase seed bank, ensuring survival. This study evaluated the persistence of Italian ryegrass seeds subjected to burial depths over time. Experiments were carried out in the field for two years in randomized block experimental design with four repetitions. Dormant seeds harvested from mother-plants were put in nylon bags containing soil. Previously, seed viability was evaluated in a 1 % tetrazolium solution, and 50 viable seeds by repetition were buried at 0.5, 5.0, 10, and 20 cm depths. Seed persistence was evaluated by the percentage of deteriorated and remaining seeds, non-dormant seeds, abnormal seedlings, and viable and non-viable dormant seeds at 0, 30, 60, 90, 180, 360, 540, and 720 days after burial (DAB). Seed persistence increased at 10 and 20 cm of burial depth compared to seeds in the soil layers up to 5 cm. Moreover, burial depth at 10 and 20 cm showed lower percentage of deteriorated seeds (10 % lower) compared to 0.5 cm at 360 DAB. For non-dormant seeds, a higher percentage was found at 90 DAB, regardless of seed burial depth. Dormancy breakage occurred until 180 DAB, and more rapidly at 10 and 20 cm depths. At 540 DAB, more than 95 % of seeds were unviable, demonstrating short persistence of Italian ryegrass in the soil seed bank

Seletividade de associações e doses de herbicidas em pós emergência do trigo

The main weeds in wheat are wild radish and ryegrass, and its post-emergence control is based on herbicides inhibiting the enzyme acetolactate synthase (ALS) and acetyl coenzyme A carboxase (ACCase), which as a function of resistance limits the control options. Herbicide combinations have been used for post-emergence of wheat; however, the effects of herbicidal combinations are poorly understood. The objective of this work was to evaluate the selectivity of wheat to herbicide associations and rates applied in post-emergence. Three field experiments were carried out in a no tillage system, in a randomized complete block design with three replicates. The experiments were conducted in Santa Bárbara do Sul-RS, Cruz Alta-RS and Tupanciretã-RS. Rates and associations between the 2,4-D herbicides, metsulfuron-methyl, iodosulfuron, pyroxsulam and saflufenacil applied in wheat tillering were studied. The evaluated variables were phytotoxicity at seven, 14, 21 and 35 days after application (DAA), yield (kg ha-1) and hectoliter weigh (HW). The data were analyzed together. At 35 DAA, the highest phytotoxicities were observed for metsulfuron methyl at the dose of 9 g a.i. ha-1 and for saflufenacil associated with metsulfuron methyl. The results of yield demonstrate that the association between 2,4-D and metsulfuron-methyl, saflufenacil isolated or associated with metsulfuron-methyl, and iodosulfuron are selective for wheat. Metsulfuron methyl at rates of 6 and 9 g a.i. ha-1 and pyroxsulam caused a significant reduction in wheat yield and were not considered selective. However, the hectoliter weight of the grains was not influenced by herbicides used of this study.As principais plantas daninhas encontradas na cultura do trigo são o nabo e o azevém, e seu controle em pós-emergência é baseado em herbicidas inibidores da enzima acetolactato sintase (ALS) e acetil coenzima A carboxilase (ACCase) que, em função da resistência, limita as opções de controle. Associações de herbicidas têm sido utilizadas em pós-emergência do trigo, porém, seus efeitos na cultura são pouco conhecidos. O objetivo deste trabalho foi avaliar a seletividade de associações de herbicidas e doses aplicados em pós-emergência do trigo. Foram realizados três experimentos a campo em sistema de semeadura direta, no delineamento de blocos ao acaso com três repetições. Os experimentos foram conduzidos nos municípios de Santa Bárbara do Sul-RS, Cruz Alta-RS e Tupanciretã-RS. Foram estudadas doses e associações entre os herbicidas 2,4-D, metsulfuron-methyl, iodosulfuron, piroxsulam e saflufenacil aplicados no perfilhamento do trigo. As variáveis avaliadas foram fitotoxicidade aos sete, 14, 21 e 35 dias após a aplicação (DAA), rendimento de grãos (kg ha-1) e peso hectolitro dos grãos de trigo (PH), sendo os dados dos três experimentos analisados de forma conjunta. Aos 35 DAA as maiores fitotoxicidades foram observadas para metsulfuron-methyl na dose de 9 g i.a. ha-1 e para saflufenacil associado ao metsulfuron-methyl. Os resultados de rendimento de grãos demonstraram que a associação entre 2,4-D e metsulfuron-methyl, saflufenacil isolado ou associado à metsulfuron-methyl e o iodosulfuron-methyl foram seletivos para o trigo. O aumento da dose de metsulfuron-methyl (6 e 9 g i.a. ha-1) e a dose de registro de piroxsulam causaram redução significativa na rendimento de grãos de grãos de trigo na média dos três experimentos. O PH dos grãos de trigo não foi influenciado pelos herbicidas estudados

Technical effectiveness and economic return of the glyphosate-resistant hairy fleabane management in soybean pre-emergence

A liberação comercial da soja Roundup Ready® favoreceu o manejo de plantas daninhas e possibilitou o cultivo da soja RR® e a aplicação do glyphosate em pós-emergência da cultura. No entanto, o uso intensivo deste herbicida selecionou biótipos de buva resistentes e dificultou o controle. Muitos trabalhos avaliam a eficiência técnica de herbicidas, porém, na maioria das vezes, o retorno econômico não é analisado na tomada de decisão sobre a escolha dos herbicidas a serem aplicados. O objetivo do trabalho foi avaliar a eficiência técnica e o retorno econômico da aplicação de associações e doses de herbicidas no manejo de buva resistente ao glyphosate em pré-emergência da soja. O experimento foi conduzido à campo no delineamento de blocos ao acaso com quatro repetições. Os tratamentos consistiram de associações entre glyphosate, 2,4-D, saflufenacil, diclosulam, chlorimuron-ethyl e flumioxazin. As variáveis analisadas foram controle de buva e fitotoxicidade na soja aos 7, 14, 21 e 35 dias após a aplicação e o rendimento de grãos da soja. O retorno econômico dos tratamentos foi calculado em função do custo dos herbicidas e do rendimento de grãos da soja. Os resultados de controle e rendimento demonstraram que a associação de glyphosate, chlorimuron-ethyl, flumioxazin e 2,4-D e, glyphosate, chlorimuron-ethyl, 2,4-D e saflufenacil apresentaram as melhores respostas de eficiência técnica e, a aplicação do glyphosate, chlorimuron-ethyl e 2,4-D apresentou o melhor retorno econômico. Entretanto, o aumento nas doses de chlorimuron-ethyl e sua associação com flumioxazin não melhorou o controle da buva.The commercial release of the Roundup Ready® soybean helped the management of weeds and allowed the application of glyphosate during the post-emergence of the culture. However, the intensive use of this herbicide selected resistant hairy fleabane biotypes and hindered control. Many works evaluate the technical effectiveness of herbicides, however, most of the times; the economic return is not analyzed when making decisions about the choice of which herbicide to apply. The aim of this work was to evaluate the technical effectiveness and the economic return of applying herbicide associations and rates in the management of glyphosate-resistant hairy fleabane, in soybean pre-emergence. The experiment was carried out in randomized block design with four replicates. Treatments consisted in associations among glyphosate, 2.4-D, saflufenacil, diclosulam, chlorimuron-ethyl and flumioxazin. The analyzed variables were hairy fleabane control and phytotoxicity on soybean on 7, 14, 21 and 35 days after the application and yield of soybean. The economic return of treatments was calculated according to the cost of the herbicides and the soybean yield. Results about control and yield shows that the association of glyphosate, chlorimuron-ethyl, flumioxazin and 2.4-D and of glyphosate, chlorimuron-ethyl, 2.4-D and saflufenacil presented the best technical effectiveness response and the use of glyphosate, chlorimuron-ethyl and 2.4-D presented the best economic return. However, the increase in chlorimuron-ethyl rates and its association with flumioxazin did not improve the control of hairy fleabane

Characterization biotypes of Raphanus sativus L. resistant and susceptible to inhibiting herbicides Acetolactate sinthase.

The Raphanus sativus (fodder radish) is a species of winter that is characterized as weed and can be used as ground cover, before winter and summer crops. His presence, like weed in areas for grain production can cause damage due to its ability to compete. This species is normally controlled with ALS inhibitor herbicides such as enzyme-methyl iodosulfurom that due to the continued use of selected resistant biotypes. Therefore, the research objectives were to determine the dose required to control 50% of the population (C50) and reduce 50% of the mass production of dry matter of shoots (GR50) of resistant biotypes, for the susceptible biotype; check alternative herbicides for control of resistant biotypes; checking the resistance mechanism through the activity of the ALS enzyme, gene sequencing of the ALS enzyme response biotypes and applying the cytochrome P450 monooxygenase inhibitor metabolism; and estimate the adaptive value of susceptible biotypes resistant and iodosulfurom methyl-sodium. For this, experiments were conducted in a greenhouse and laboratories belonging to UFPel and Wheat Embrapa Passo FundoRS using fodder radish seeds collected in northern crops and gaucho northwest where control failures occurred after the use of iodosulfurom methyl sodium. The results demonstrate that to obtain equivalent control of resistant biotypes (B4 and B13), it is necessary dose of iodosulfurom methyl sodium than 89 252 times higher than that required for the susceptible biotype (B1). Biotypes B4 and B13 are controlled with the alternative herbicide glufosinate ammonium, paraquat dichloride, diuron + paraquat dichloride, glyphosate, saflufenacil, metribuzin, bentazon, 2,4-D amine, mesotrione, tembotrione, atrazine and fomesafen belonging to mechanisms separate action. However, B4 and B13 biotypes show resistance to metsulfurom-methyl, nicosulfuron, chlorimurom-ethyl, imazethapyr, cloransulam-methyl, flucarbazone sodium and bispyribac-sodium, all herbicides inhibitors of ALS enzyme, confirming the cross-resistance. In the assay of ALS enzyme activity, fodder radish biotypes have similar affinity for the enzyme, however B4 and B13 have greater Vmax when compared to susceptible; inhibiting ALS enzyme activity in the presence of iodosulfurom methyl-sodium herbicide showed 50% inhibition is required 0.65 and 0.82 uM to B4 and B13 respectively, resulting in a resistance factor 15 and 19 when compared with B1. It was found that mutation of resistant biotypes presented with Trp574 substitution of leucine amino acid tryptophan by confirming that the resistance was due to sensitivity of the ALS enzyme. We observed the occurrence of the silent mutations Ala122 in all biotypes which the codon GCC was substituted for GCT without causing changes in the amino acid. Biotypes have no metabolism iodosulfurom methyl-sodium cytochrome P450 complex when inhibited by the insecticide malathion or piperonyl butoxide (PBO). The fodder radish susceptible biotypes (B1) and resistant (B4) to iodosulfurom-methyl herbicide sodium generally had similar fitness.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESO Raphanus sativus (nabo) é uma espécie de inverno que se caracteriza como planta daninha, podendo ser usada como cobertura de solo, antes dos cultivos de inverno e verão. Sua presença, como planta daninha, em áreas destinadas a produção de grãos pode causar prejuízos, devido à sua capacidade de competição. Esta espécie é normalmente controlada com herbicidas inibidores da enzima ALS como o iodosulfurom-metílico que, devido o uso continuado, selecionou biótipos resistentes. Diante disso, os objetivos da pesquisa foram determinar a dose necessária para controlar 50% da população (C50) e reduzir 50% da produção de massa da matéria seca da parte aérea (GR50) dos biótipos resistentes, em relação ao biótipo suscetível; verificar herbicidas alternativos para controle de biótipos resistentes; verificar o mecanismo de resistência através da atividade da enzima ALS, do sequenciamento do gene da enzima ALS e da resposta dos biótipos à aplicação de inibidores do metabolismo da citocromo P450 monooxigenase; e, estimar o valor adaptativo dos biótipos suscetível e resistentes ao iodosulfurom-metílico. Para isso, foram realizados experimentos em casa de vegetação e laboratórios pertencentes à UFPel e a Embrapa Trigo, utilizando sementes de nabo coletadas em lavouras do norte e noroeste gaúcho onde ocorreram falhas de controle após o uso do iodosulfurom-metílico. Os resultados demonstram que, para obter-se controle equivalente dos biótipos resistentes B4 e B13, é necessária dose de iodosulfurommetílico superior a 89 e 252 vezes àquela necessária para o biótipo suscetível (B1). Os biótipos B4 e B13 são controlados com os herbicidas alternativos glufosinato de amônio, dicloreto de paraquate, diurom+dicloreto de paraquate, glifosato, saflufenacil, metribuzim, bentazona, 2,4-D amina, mesotriona, tembotriona, atrazina e fomesafem, pertencentes a mecanismos de ação distintos. Todavia, os biótipos B4 e B13 apresentam resistência a metsulfurom-metílico, nicosulfurom, clorimurometílico, imazetapir, cloransulam-metílico, flucarbazona sódio e bispiribaque-sódico, todos herbicidas inibidores da enzima ALS, confirmando a resistência cruzada. No ensaio da atividade da enzima ALS, os biótipos de nabo apresentam similar afinidade com a enzima, entretanto B4 e B13 apresentam Vmáx superior quando comparados ao suscetível; a inibição da atividade da enzima ALS na presença do herbicida iodosulfurom-metílico mostrou que para 50% da inibição é necessário 0,65 e 0,82 µM para o B4 e B13 respectivamente, resultando num fator de resistência de 15 e 19 quando comparados com o B1. Constatou-se que os biótipos resistentes apresentaram mutação da Trp574 com substituição do aminoácido Triptofano por Leucina confirmando que a resistência deve-se a insensibilidade da enzima ALS. Observou-se a ocorrência de mutações silenciosas na Ala122 em todos os biótipos onde o códon GCC foi substituído por GCT sem resultar em alteração do aminoácido. Os biótipos não apresentam metabolismo do iodosulfurom-metílico pelo complexo citocromo P450 quando inibidos pelos inseticidas malathion ou butóxido de piperonila (PBO). Os biótipos de nabo suscetível (B1) e resistentes (B4) ao herbicida iodosulfurom-metílico sódio, em geral, apresentaram valor adaptativo similar

Fitness costs of susceptible and resistant radish biotypes to ALS-inhibitor herbicides

Radish is an important weed that causes yield reduction in winter crops in southern Brazil. The control chemical of radish is an important and essential step to prevent damage on crops. However the intensive use of ALS-inhibitors herbicides favors the selection resistant biotypes. The selection can influence the adaptive traits of biotypes with physiological changes and growth variables and plant reproduction. The objective of the study was compare the fitness costs of susceptible and resistant radish biotypes to ALS-inhibitors herbicides. The experiment was conducted in greenhouse using completely randomized design with five replications. The treatments were arranged in factorial arrangement corresponding to susceptible and resistant biotypes (B1 and B4) and nine sampling times (14, 28, 42, 56, 70, 84, 98, 112 and 126 days after emergency), respectively. The variables evaluated were plant height, shoot dry matter, root dry matter, total dry matter, leaf area, growth rate, relative growth rate, leaf area ratio, number of siliques and seeds produced per plant. The results showed that the resistant biotype (B4) had no fitness costs when compared to the susceptible biotype (B1)

Mutation of Trp-574-Leu ALS gene confers resistance of radish biotypes to iodosulfuron and imazethapyr herbicides

Acetolactate synthase inhibitors are the main group of herbicides used in winter crops in Southern Brazil where their intensive use has selected for herbicide-resistant biotypes of radish. The resistance affects the efficacy of herbicides, and identifying the resistance mechanism involved is important for defining management strategies. The aim of this study was to elucidate the resistance mechanism of radish biotypes by quantifying the enzyme activity, ALS gene sequencing and evaluating the response of biotypes to iodosulfuron and imazethapyr herbicide application after treatment with a cytochrome P450 monooxygenase inhibitor. The susceptible (B1) and resistant (B4 and B13) biotypes were from wheat fields in the Northwest of Rio Grande do Sul State. The results demonstrated that the enzyme affinity for the substrate (KM) was not affected in biotypes B4 and B13 but that the Vmax of the resistant biotypes was higher than that of biotype B1. The resistant biotypes showed no differential metabolic response to iodosulfuron and imazethapyr herbicides when inhibited by malathion and piperonyl butoxide. However, gene sequencing of ALS showed a mutation at position 574, with an amino acid substitution of tryptophan for leucine (Trp-574-Leu) in resistant biotypes.