Ana Claudia Langaro

Changes in Photosynthesis and Oxidative Stress in Wheat Plants Submmited to Herbicides Application

The use of herbicides, even in tolerant crops, can cause stress evidenced by increase phytotoxicity affecting growth and development. The objectives of this study were to evaluate herbicides effect from different mechanisms of action in photosynthetic and oxidative stress parameters, as well visual phytotoxicity and wild radish control in wheat crop, cultivar Quartzo. Two trials were conducted where the first one evaluated the photosynthetic parameters on wheat plants in two seasons collection, following the application of herbicides bentazon, clodinafop, iodosulfuron, metribuzin, metsulfuron and 2,4-D; and the second one evaluated wild radish (Raphanus sativus) control, wheat phytotoxicity and yield due to bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D herbicides application. Photosynthetic rate, stomatal conductance and transpiration were negatively affected by metribuzin, metsulfuron and 2,4-D herbicides at 24 and 120 HAS (hours after spraying) compared to control. Oxidative stress was similar or lower to control, when herbicide was applied and, in general, there was no difference between application times. Lipid peroxidation, catalase activity and phenols were higher in the first collection time. The application of herbicides iodosulfuron and 2,4-D reduces chlorophylls and carotenoids in wheat. Herbicides bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D are selective to wheat, cultivar Quartzo and do not affect wheat yield. 2,4-D, metribuzin and iodosulfuron are more efficient for wild radish control.

Biochemical and Physiological Changes in Rice Plants Due to the Application of Herbicides1

The application of herbicides, even if selective, can cause biochemical and physiological changes, resulting in oxidative stress. This stress comes from the accumulation of reactive oxygen species produced due to exposure to the herbicide. However, plants have developed defense strategies, which can be enzymatic or non-enzymatic. The objective of this study was to evaluate the morphological and metabolic changes such as photosynthetic parameters, oxidative damage and antioxidant enzyme activity of rice plants after applying herbicides. For this, a study was conducted in a greenhouse and laboratory and the treatments consisted of application of imazapic + imazapyr, quinclorac, bentazon, cyhalofop-butyl, penoxsulan, bispyribac-sodium and carfentrazone-ethyl, in addition to control without herbicide. The phytotoxicity in plants was strong and there was a reduction in photosynthesis, stomatal conductance and efficiency of water use in plants treated with carfentrazone-ethyl. Furthermore, the application of carfentrazone-ethyl resulted in lower chlorophylls and carotenoids and increased lipid peroxidation and proline accumulation. Changes in the activity of enzymes belonging to the antioxidant system were inspected by applying herbicides. The application of herbicide alters the physiology of rice plants, triggering responses to oxidative stress, which are more pronounced when used carfentrazone-ethyl.

Relative competitiveness of soybean cultivars with barnyardgrass

The aim of this work was to evaluate the competitiveness between soybean cultivars and barnyardgrass, based on morphological and physiological characteristics of species. The experiments were conducted in completely randomized experimental design, with 4 replications. In the first study, for both soybean and barnyardgrass, it was determined the population of plants in which shoot dry matter became constant and independent of the population (16 plants∙pot−1 or 400 plants∙m−2). In the second study, 2 experiments were conducted to evaluate the competitiveness of BMX Apolo RR and BMX Potencia RR soybean cultivars with barnyardgrass plants, both carried out in replacement series under different proportions of plants∙pot−1 (100:0; 75:25; 50:50; 25:75 and 0:100) between the crop and the weed. The analysis of the species competitiveness was determined through diagrams applied to replacement series experiments and use of relative competitiveness indexes. At 44 days after the emergence of species, the physiological and morphological parameters of the crop and the weed were evaluated. The BMX Apolo RR and BMX Potencia RR soybean cultivars show similar competitiveness when competing with the barnyardgrass; therefore, the ability of one species to interfere on another is equivalent. For plant height, barnyardgrass displays higher competitiveness compared to BMX Apolo RR, with early cycle and short height. The intraspecific competition is more important to barnyardgrass than interspecific competition with soybean cultivars, resulting in negative effects on the morphological and physiological characteristics of species.

Habilidade competitiva relativa de arroz irrigado com arroz-vermelho suscetível ou resistente ao herbicida imazapyr + imazapic

The intensive use of herbicides with the same mechanism of action has selected resistant weeds, among which is the red rice (Oryza sativa L.) after the use of the formulated herbicide mixture of imazapyr and imazapic. The competition of weeds leads to usually increasing yield losses of crops, the more similar the morphological and physiological characteristics between weed and crop. Moreover, the competitive ability of the biotype is generally modified by the resistance characteristic; besides, the knowledge of competitive ability is fundamental to understand the dynamics of the resistant population. Therefore, the aim of this research was to study the competitive ability of red rice biotypes that are resistant and susceptible to imazapyr and imazapic herbicide with rice, using the series substitution method. Experiments were conducted with Puita INTA CL cultivar competing with susceptible or resistant biotypes of red rice. The total plant populations per pot were of 24, similar to 942 plants m-2. For red rice that is resistant or susceptible to herbicide, the interspecific competition is favorable with regard to intraspecific competition, while for the irrigated rice the competitor is independent. Generally, the Puita INTA CL cultivar presents competitive ability equivalent to red rice biotypes that are susceptible or resistant to imazapyr and imazapic herbicide, competing for the same resources from the environment.

RELATIVE COMPETITIVENESS OF GOOSEGRASS BIOTYPES AND SOYBEAN CROPS

The goosegrass (Eleusine indica (L.) Gaertn) is an annual plant that has a low-level resistance to glyphosate (LLRG), resulting in control failure in genetically modified soybean crops for resistance to this herbicide. Alleles related to resistance may cause changes in the plant biotype, such as inferior competitive ability. Thus, the objective of this work was to evaluated the competitive ability of soybean crops and susceptible and resistant (LLRG) goosegrass biotypes. Replacement series experiments were conducted with soybean crops and goosegrass biotypes. The ratios of soybean to susceptible or resistant (LLRG) goosegrass plants were 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 481 plants m. The leaf area, plant height and shoot dry weight were evaluated at 40 days after emergence of the soybean crops and weeds. The soybean crop had superior competitive ability to the susceptible and resistant (LLRG) goosegrass biotypes. The soybean crop showed similar competitive ability in both competitions, either with the susceptible or resistant (LLRG) goosegrass biotypes. The intraspecific competition was more harmful to the soybean crop, while the interspecific competition caused greater damage to the goosegrass biotypes competing with the soybean crop.

Initial growth and competitive ability of yellow nutsedge and irrigated rice

Plantas daninhas causam grande reducao de produtividade das lavouras de arroz irrigado. A especie Cyperus esculentus (tiririca-amarela) e adaptada ao ambiente irrigado. Informacoes sobre a habilidade competitiva da daninha com a cultura, e sua adaptacao ambiental, sao escassas. Os objetivos da pesquisa foram determinar o crescimento inicial e a habilidade competitiva de tiririca-amarela e arroz irrigado, em funcao do ciclo vegetativo das cultivares. Para isso, foram conduzidos estudos de adaptacao e competicao, em delineamentos completamente casualizados, em casa de vegetacao no ano agricola 2010/11. Para o estudo de crescimento inicial, os tratamentos constituiram-se da combinacao fatorial de biotipo de tiririca-amarela e duas cultivares de arroz irrigado em funcao do ciclo vegetativo (BRS Querencia: ciclo precoce; e, IRGA 424: ciclo medio) e seis epocas de avaliacao (10, 20, 30, 40, 50, e 60 dias apos a emergencia). Avaliou-se: estatura, area foliar, massa da materia seca da parte aerea e massa da materia seca de raizes. Para o estudo de habilidade competitiva foram utilizadas a cultivar de arroz BRS Querencia e biotipo de tiririca-amarela, testados em diferentes proporcoes (100:0, 75:25, 50:50, 25:75 e 0:100). Avaliou-se area foliar e massa da materia seca da parte aerea. Em geral, as cultivares de arroz estudadas possuem crescimento inicial equivalente a tiririca-amarela. A cultivar IRGA 424 possui estatura inferior a planta daninha tornado o controle prioritario para a cultivar. Para a cultura do arroz, a competicao intraespecifica e mais importante, enquanto que para a planta daninha a competicao interespecifica e a mais pronunciada.

Oxidative stress caused by the use of preemergent herbicides in rice crops

Among the methods of weed control, stands out chemical control. However, even selective, herbicides can trigger the production of reactive species of oxygen and cause oxidative stress. The aim of the study was to evaluate changes in photosynthetic parameters, oxidative damage, antioxidant enzyme activity and altered metabolism of rice plants after applying pre-emergent herbicides. The experiment was conducted in a greenhouse and herbicides used were oxadiazon, pendimethalin and oxyfluorfen, beyond the control without herbicide. There was a reduction of photosynthetic rate and efficiency of carboxylation, compared to the control, when applied herbicides oxyfluorfen and pendimethalin. The major lipid peroxidation and proline accumulation was observed for the herbicide oxyfluorfen. The oxyfluorfen and oxadiazon herbicides also resulted in increased activity of superoxide dismutase, compared to control. When evaluated ascorbate peroxidase activity, there was a higher enzyme activity in plants treated with oxadiazon and pendimethalin. Even selective herbicides registered for weed control in rice crops cause phytotoxicity, reduce height and alter the metabolism of plants, generating reactive oxygen species, which activate enzymatic and non-enzymatic defense systems and result in the degradation of photosynthetic pigments and in reduced protein content.

Valor adaptativo e habilidade competitiva de azevém resistente e suscetível ao iodosulfuron em competição com o trigo

O objetivo deste trabalho foi identificar e comparar valores adaptativos dos biotipos de azevem (Lolium multiflorum) resistente e suscetivel ao herbicida iodosulfuron e avaliar sua habilidade competitiva com o trigo (Triticum aestivum). Para avaliar o valor adaptativo, os biotipos foram semeados em vasos e coletados a cada 10 dias apos a emergencia, ate os 80 dias. Em cada coleta, avaliaram-se estatura, area foliar e massa seca da parte aerea, e, a partir destas avaliacoes, foram calculadas variaveis indiretas para comparar o crescimento entre os biotipos. A habilidade competitiva foi determinada em experimento de serie de substituicao, tendo-se variado a proporcao da cultura e do competidor. As proporcoes testadas foram: 100:0 (estande puro do trigo), 75:25, 50:50, 25:75 e 0:100% (estande puro do biotipo de azevem resistente ou suscetivel); ja as variaveis avaliadas foram area foliar e massa seca. Os resultados dos estudos comparativos de crescimento mostraram similaridade entre os biotipos de azevem resistente e suscetivel ao iodosulfuron, o que nao caracterizou efeito pleiotropico decorrente da resistencia. Quanto a habilidade competitiva, a competicao interespecifica e prejudicial para o biotipo resistente, enquanto, para o biotipo suscetivel, independe o competidor. A cultura do trigo mostra habilidade competitiva superior a dos biotipos de azevem resistente e suscetivel.