ABSTRACT The use of auxin mimics herbicides in agriculture is widespread in a great diversity of crops. The indiscriminate use of herbicides can cause adverse effects in the plants. Among the plant species that stand out for being highly competitive and resistant to biotic and abiotic stresses, it is the brazilian peppertree (Schinus terebinthifolius Raddi.). The objective of this work was to evaluate the phytotoxic and photosynthetic alteration effects of different rates simulating the drift of the herbicides 2,4-D and Dicamba in brazilian peppertree seedlings. The experiment was carried out in a completely randomized design with four replications. The treatments were arranged in 2 x 8 factorial design (herbicide x doses). The factor herbicide consisted the herbicides 2,4-D and Dicamba, and, the factor doses eight percentages of the herbicide applied. Phytotoxicity and alteration of photosynthetic and fluorescence of chlorophyll a parameters were evaluated. Increased rate of the 2,4-D and Dicamba cause phytotoxicity to the plants, whose Dicamba promotes greater injuries. Dicamba was the herbicide that caused the greatest damage to the photosynthetic apparatus on brazilian peppertree plants, while for 2,4-D the plants showed higher recovery potential after herbicidal exposure.

Resumo O desenvolvimento de plantas mais eficientes no uso de nutrientes será fundamental para a agricultura nos próximos anos. O objetivo deste trabalho foi definir um marcador fisiológico do status nutricional do P para clones de batata cultivados fora do solo e in vitro, visando facilitar o processo de seleção de clones mais eficientes no uso de P. Para tanto, foram realizados dois experimentos com sete clones de batata (SMIC 148-A, Dakota Rose, SMINIA 793101-3, SMIB 106-7, SMIF 212-3, SMIJ 319-1 e P 150) cultivados em dois níveis de P (baixo e alto) no sistema de cultivo in vitro (1,935 e 19,346mg P L-1) e no cultivo fora do solo (2,32 e 23,2mg P L-1) usando areia como substrato. O teor de P inorgânico e a acumulação total de P na parte aérea e nas raízes parecem ser bons indicadores da condição nutricional de P em plantas de batata, tanto no cultivo fora do solo quanto no in vitro. A atividade das enzimas fosfatases ácidas (APases) nos tecidos da batata depende muito do sistema de cultivo, do clone e do órgão da planta analisado, dificultando a escolha deste como um marcador fisiológico para restrição de P em batata. A massa seca da planta de batata pode ser um bom indicador do status nutricional do P em clones cultivados fora do solo.

Abstract The development of more efficient plants in the use of nutrients will be fundamental for agriculture in the coming years. The objective of this work was to define a physiological marker of the nutritional status of P for potato clones cultivated soilless and in vitro, in order to facilitate the selection process of more efficient clones in the use of P. For this, two experiments were carried out with seven potato clones (SMIC 148-A, Dakota Rose, SMINIA 793101-3, SMIB 106-7, SMIF 212-3, SMIJ 319-1 and P 150) grown at two levels of P (low and high) in the culture systems in vitro (1.935 and 19.346mg P L-1) and in soilless (2.32 and 23.2mg P L-1) using sand as substrate. The inorganic P content and the total accumulation of P in shoot and roots seem to be good indicators of the nutritional status of P in potato plants, both in soilless and in vitro cultivation. The activity of the acidic phosphatase enzymes (APases) in the tissues of the potato depends very much on the culture system, the clone and the organ of the analyzed plant, making it difficult to choose it as a physiological marker for restriction of P in potatoes. The dry mass of the potato plant may be a good indicator of the nutritional status of P in clones grown soilless.

RESUMO: O objetivo deste trabalho foi avaliar a interação entre herbicidas associados ao saflufenacil para o controle de capim-arroz e a determinação do efeito dos herbicidas sobre os parâmetros fotossintéticos e de fluorescência de clorofila. O experimento foi conduzido em casa de vegetação em esquema fatorial 2x8, cujo fator A testou os biótipos resistente e suscetível; e o fator B os herbicidas: saflufenacil (70 g i.a. ha-1), clomazone (180 g i.a. ha-1), imazapyr+imazapic (73,5+24,5 g i.a. ha-1), cyhalofop (360 g i.a. ha-1), as associações desses com saflufenacil, e testemunha sem tratamento. Foi avaliado o controle aos 7, 14, 21 e 28 dias após a aplicação dos herbicidas (DAA), massa seca da parte aérea aos 28 DAA, avaliação de parâmetros fotossintéticos com analisador de gás infravermelho (IRGA) e emissão de fluorescência da clorofila a 24 e 48 horas após aplicação dos tratamentos, respectivamente, e interação dos herbicidas. A associação de saflufenacil com herbicidas testados na maior parte não modificou a resposta dos herbicidas para o controle de capim-arroz em ambos os biótipos. O biótipo resistente apresentou menor efeito negativo nos processos de fluorescência de clorofila e parâmetros de fotossíntese na associação de herbicidas com saflufenacil. O herbicida cyhalofop associado ao saflufenacil demonstra ser eficiente para o controle de capim-arroz suscetível e resistente a ALS.

ABSTRACT: The objectives of this research were to evaluate the interaction between herbicides mixed with saflufenacil for the control of barnyardgrass and to determine the effect on photosynthetic and chlorophyll fluorescence parameters. The experiment was conducted in a greenhouse in a 2x8 factorial scheme, whose factor A tested resistant and susceptible biotypes; and factor B the herbicides: saflufenacil (70 g a.i. ha-1), clomazone (180 g a.i. ha-1), imazapyr + imazapic (73.5 + 24.5 g a.i. ha-1), and cyhalofop (360 g a.i. ha-1), the mixtures of these herbicides with saflufenacil, and control without treatment. Weed control was assessed 7, 14, 21 and 28 days after herbicide application (DAA), as well as shoot dry matter at 28 DAA, photosynthetic parameters using infrared gas analyzer (IRGA), and emission of chlorophyll a fluorescence after 24 and 28 hours of application of treatments, respectively, and interaction of herbicides. Combination of saflufenacil with the herbicides tested in general did not change the response of both barnyardgrass biotypes to the herbicides used. The resistant biotype showed a lower negative effect on chlorophyll fluorescence and photosynthesis parameters in the combination of herbicides with saflufenacil. The herbicide cyhalofop was effective for the control of ALS-susceptible and resistant barnyardgrass.

ABSTRACT Potato cultivation is widespread around the world, being exposed to several abiotic stresses, including soils with high aluminum (Al) availability. Silicon (Si) is recognized for alleviating the stress caused by Al in various plant species. Thus, the aim of this study was to investigate the potential of Si to mitigate the oxidative stress caused by Al in potato genotypes, exhibiting differential sensitivity toward this element. Plants of the Al-sensitive genotype (SMIJ319-7) and Al-tolerant genotype (SMIF212-3) were grown for two weeks in a hydroponic system with the nutrient solution containing combinations of Al (0 and 1.85 mM) and Si (0, 0.5 and 1.0 mM). At the end of the experiment, photosynthetic parameters, pigment content, root and shoot growth, superoxide dismutase and guaiacol peroxidase activity and lipid peroxidation were evaluated. In both potato genotypes Al inhibited root and shoot growth and decreased all photosynthetic parameters and superoxide dismutase activity. Silicon was able to partially alleviate the damage caused by Al in parameters of root growth in the Al-tolerant genotype while increasing the activity of antioxidant enzymes and mitigating the Al-induced damage to membrane lipids in roots and shoot in both genotypes. The Al-tolerant genotype showed greater water use efficiency and transpiration rate in control conditions as compared to the Al-sensitive genotype. These data indicate that Si application can improve the defense ability of the tested potato genotypes against Al toxicity and that the Al-tolerant genotype is more responsive to Si.

RESUMO: O carbono rizosférico resultado da exsudação radicular é um dos substratos utilizados pela microbiota do solo, refletindo-se nas emissões de metano (CH4) em ambientes anóxicos, como no cultivo de arroz irrigado. Com o aumento da capacidade fotossintética da planta no período reprodutivo, ocorre acúmulo maior de biomassa, que por sua vez, impulsiona aumento na taxa de exsudação radicular. Entretanto, variações genotípicas nos aspectos fisiológicos das plantas de arroz podem se relacionar com a quantidade de exsudatos radiculares. Foram avaliadas dez cultivares de arroz irrigado quanto a taxa de exsudação de carbono orgânico total (TEXCOT), matéria seca da parte aérea (MSPA) e variáveis fisiológicas relacionadas com a fotossíntese no período de florescimento pleno. Dois experimentos foram conduzidos na casa de vegetação do Departamento de Solos da UFSM em delineamento experimental inteiramente casualizado. As cultivares apresentaram diferenças significativas na TEXCOT, na MSPA e em todas as variáveis fisiológicas, bem como, correlações positivas e significantes entre TEXCOT e as variáveis fisiológicas, sendo que as cultivares de ciclo precoce se mostraram mais ineficientes nas variáveis fisiológicas refletindo em valores reduzidos de TEXCOT e MSPA, enquanto que as cultivares de ciclo médio se mostraram mais eficientes com reflexos em maiores TEXCOT e MSPA.

ABSTRACT: Rhizospheric carbon resulting from root exudation is one of the substrates used by the soil microbiota, and reflects methane (CH4) emissions in anoxic environments such as irrigated rice cultivation. With the increase of the photosynthetic capacity of the plant in the reproductive period, there is greater accumulation of biomass which, in turn, increases the rate of root exudation. However, genotypic variations in the physiological aspects of rice plants may be related to the amount of root exudates. Ten cultivars of irrigated rice were evaluated for the exudation rate of total organic carbon (EXRToc), shoot dry matter (SDM), and physiological variables related to photosynthesis during the full flowering (blooming) period. Two experiments were conducted in the greenhouse of the Department of Soils of the UFSM (University of Santa Maria, Santa Maria, RS, Brazil) in a completely randomized experimental design. The cultivars presented significant differences in EXRToc, SDM, and all physiological variables as well as positive and significant correlations between EXRToc and physiological variables. Early cultivars were more inefficient in the physiological variables reflecting reduced values of EXRToc and SDM whereas medium-cycle cultivars were more efficient with larger EXRToc and SDM reflections.

O uso intenso de herbicidas com o mesmo mecanismo de ação na cultura do arroz (Oryza sativa L.) tem selecionado biótipos resistentes, como, por exemplo, o arroz-vermelho (planta daninha) resistente aos herbicidas imidazolinonas. Por essa razão, este trabalho foi desenvolvido com o objetivo de avaliar a resistência de arroz-vermelho ao herbicida imazapyr + imazapic, na região sul do Rio Grande do Sul, e o controle do biótipo resistente de arroz-vermelho com os herbicidas alternativos clethodim e glyphosate. Foram realizados três experimentos, em delineamento casualizado, arranjados em esquema fatorial. No primeiro experimento, o fator A testou biótipos de arroz-vermelho [ORYSA 184 (resistente) e ORYSA 188 (susceptível)], o fator B comparou herbicidas (imazapyr + imazapic, clethodim e glyphosate) e o fator C avaliou doses dos herbicidas (0; 0,5; 1; 2; 4; 8; 16 e 32 vezes a dose recomendada). No segundo, compararam-se biótipos de arroz-vermelho e doses do herbicida imazapyr + imazapic (0; 0,5; 1; 2; 4; 8; 16; 32 e 64 vezes a dose recomendada). No terceiro, testaram-se biótipos de arroz-vermelho e doses diferentes do herbicida imazapyr + imazapic para cada biótipo. O biótipo ORYSA 184 é resistente ao imazapyr + imazapic, quando aplicada a dose máxima de registro e estádio indicado. Os herbicidas clethodim e glyphosate, detentores de mecanismos de ação alternativos, controlam o biótipo resistente ORYSA 184 de arroz-vermelho.

The intenseuse of herbicides with the same action mechanism in rice (Oryza sativa L.) has selected resistant biotypes, such as red rice (weed) resistant to imidazolinone herbicides. Therefore, the objective of this work was to evaluate the resistance of red rice to the imazapyr + imazapic herbicide in the southern region of Rio Grande of Sul, Brazil, and the control of the red rice resistant biotype with the alternative herbicides, clethodim and glyphosate. Three experiments were carried out in a completely randomized design, arranged in a factorial design. In the first experiment, the factor A tested biotypes of red rice [ORYSA 184 (resistant) and ORYSA 188 (susceptible)], factor B compared herbicides (imazapyr + imazapic, clethodim and glyphosate) and factor C evaluated dosages of herbicide (0, 0.5, 1, 2, 4, 8, 16 and 32 times the recommended dosage). The second experiment compared biotypes of red rice and dosages of the imazapyr + imazapicherbicide (0, 0.5, 1, 2, 4, 8, 16, 32 and 64 times the recommended dosages). The third experiment tested biotypes of red rice and different doses of the imazapyr + imazapic for each biotype. The biotype ORYSA 184 is resistant to imazapic + imazapyr when applied at the maximum indicated record and stadium dose. The herbicides glyphosate and clethodim, holders of alternative mechanisms of action, control the red rice resistant biotype ORYSA 184.

O objetivo deste trabalho foi determinar os períodos de interferência de plantas daninhas no crescimento e desenvolvimento do eucalipto. O experimento foi realizado em campo, de agosto de 2006 a abril de 2008, com plantio de híbrido de Eucalyptus grandis x Eucalyptus urophylla, em delineamento de blocos ao acaso, com três repetições. Os tratamentos consistiram de períodos de convivência e de controle das plantas daninhas com o eucalipto. No tratamento com convivência, a cultura foi mantida em presença de plantas daninhas por intervalos iniciais crescentes de 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 e 360 dias após o transplantio (DAT) do eucalipto. No tratamento controle, o eucalipto foi mantido livre de plantas daninhas, nos mesmos intervalos descritos para a convivência, e as plantas daninhas emergidas após esses intervalos não foram mais controladas. As avaliações foram realizadas aos 360 e aos 630 DAT. A competição com as plantas daninhas causou a redução do diâmetro e da massa de matéria seca de caules e ramos. Medidas de controle das plantas daninhas, no primeiro ano de implantação da cultura do eucalipto, devem ser adotadas ao final do período anterior à interferência, que ocorre aos 107 dias após o transplante da cultura.

The objective of this work was to determine the interference periods of weeds on the growth and development of eucalyptus. The experiment was done in the field from August 2006 to April 2008, with a hybrid of Eucalyptus grandis x Eucalyptus urophylla planted in a randomized block design, with three replicates. Treatments consisted of coexistence and control periods of weeds with eucalyptus culture. During the coexistence treatment, the culture was maintained in the presence of weeds by increasing initial periods of 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 and 360 days after culture transplant (DAT). During the control treatment, the culture was maintained free from weeds for the same periods above described; weeds emerged after those intervals were no longer controlled. Evaluations were made at 360 and at 630 DAT. The competition with weeds caused reduction of the stem diameter and of the dry matter of stems and shoots. Weed control, in the first year of the eucalyptus culture, must be adopted at the end of the period before interference, which happens 107 days after the culture transplant.