ABSTRACT Ryegrass and turnip are weeds that cause high yield losses when infesting barley, thus requiring adequate management. In this context, the aim of this study was to evaluate the selectivity of different herbicide treatments and weed control in the barley crop, cultivar BRS Cauê. Two field experiments were conducted in randomized blocks, with four replications. The treatments used were: pendimethalin (800 g·ha-1), sulfentrazone + diuron (175 + 350 g·ha-1), and imazaquim (150 g·ha-1 of a. e.) applied pre-emergence; and iodosulfuron (3.5 g·ha-1), pyroxsulam (18 g·ha-1), metsulfuron-methyl (3.96 g·ha-1), 2,4-D (670 g·ha-1 of a. e.), clodinafop-propargyl (48 g·ha-1), bentazon + imazamox (600 + 28 g·ha-1), saflufenacil (49 g·ha-1), bentazon (720 g·ha-1), carfentrazone-ethyl (120 g·ha-1), and imazamox (42 g·ha-1) applied post-emergence, with two controls (one weeded and the other infested). The use of the herbicide imazaquim caused high levels of phytotoxicity in barley. Gas exchange was less responsive to herbicide applications in relation to barley phytotoxicity and productivity. Clodinafop-propargil showed the best control of ryegrass, while the herbicides iodosulfuron, pyroxsulam, metsulfurom-methyl, 2,4-D, bentazon + imazamox, saflufenacil, bentazon, carfentrazone-ethyl, and imazaquim showed high efficiency in the control of turnip species. Imazaquim caused reduction of up to 74.7% in barley grain yield. On the other hand, iodosulufuron and piroxsulam allowed the highest grain yields of the barley cultivar, BRS Cauê, by promoting partial control of ryegrass and total control of turnip species, followed by clodinafop-propargyl and metsulfuron-methyl, which controlled ryegrass and turnip, respectively, allowing an increase in yield grain in relation to the infested control.

Resumo O objetivo deste trabalho foi avaliar os efeitos de doses de metsulfurom-metílico, aplicadas em diferentes épocas, sobre as características fisiológicas e produtivas da soja (Glycine max), em dois anos agrícolas, em condições de campo, tendo-se utilizado o pepino (Cucumis sativus) como planta bioindicadora, em casa de vegetação. Os experimentos foram conduzidos em blocos ao acaso, em arranjo fatorial 4x5, com quatro repetições. O fator A foi o tempo de aplicação do herbicida (45, 30, 15 e 0 dias antes da semeadura da soja, DAS), e o fator B foi a dose de metsulfurom-metílico (0, 3,6, 5,4, 7,2 e 9,0 g ha-1 i.a.). Foram avaliadas as seguintes variáveis: fitotoxicidade, trocas gasosas, fluorescência da clorofila a e componentes de rendimento. A maior fitotoxicidade em plantas de soja é observada após o uso da maior dose de metsulfurom-metílico e com semeadura em 0 DAS. A taxa de transporte de elétrons reduz drasticamente com o aumento da dose de metsulfurom-metílico e da proximidade da semeadura, enquanto a extinção não fotoquímica, como mecanismo de defesa, aumenta em plantas de soja expostas ao transporte de herbicida de até 5,4 g ha-1. Os resíduos de metsulfurom-metílico reduzem o peso de mil grãos e a produtividade de soja em função da dose de aplicação e do período de semeadura. Para as plantas de pepino, também foram verificados efeitos negativos nas características fisiológicas. Um intervalo de mais de 45 dias é recomendado para a semeadura da soja após a aplicação de metsulfurom-metílico para dessecação.

Abstract The objective of this work was to evaluate the effects of metsulfuron-methyl rates, applied at different times, on the physiological and productive traits of soybean (Glycine max) in two crop years, in field conditions, using cucumber (Cucumis sativus) as a bioindicator plant, in greenhouse conditions. The experiments were conducted in a randomized complete block, in a 4x5 factorial arrangement, with four replicates. Factor A was the herbicide application time (45, 30, 15, and 0 days before soybean sowing, DBS), and factor B was the metsulfuron-methyl rate (0, 3.6, 5.4, 7.2, and 9.0 g ha-1 a.i.). The following variables were evaluated: phytotoxicity, gas exchange, chlorophyll a fluorescence, and yield components. The highest phytotoxicity in soybean plants is observed after the use of the highest rate of metsulfuron-methyl and with sowing at 0 DBS. The electron transport rate drastically reduces with an increasing metsulfuron-methyl rate and sowing proximity, whereas non-photochemical quenching, acting as a defense mechanism, increases in soybean plants exposed to a herbicide carryover of up to 5.4 g ha-1. Metsulfuron-methyl carryover reduces soybean 1,000-grain weight and productivity as a function of application rate and sowing period. For the cucumber plants, negative effects on physiological traits were also verified. An interval of more than 45 days is recommended for sowing soybean after metsulfuron-methyl application for desiccation.

Abstract Plant health and nutrition are strongly influenced by the availability of water. The objective of this study was to evaluate the different patterns of initial growth and nutritional efficiency of ten drought-stressed Eucalyptus clones. Water stress conditions were induced by osmotic stress, by gradual addition of polyethylene glycol 6000 over a 20-day period. Drought stress significantly reduced the dry matter of leaves, roots, and the whole plant as well as the nutritional efficiency of most clones. Clone PL040 was the least efficient in nutrient uptake and use and the most sensitive to drought stress. Interestingly, under drought stress, the drought-tolerant clones generally had high AE (absorption efficiency), but low nutrient UE (use efficiency), whereas the sensitive clones had low AE and low UE for root formation and high AE for leaf formation. In a combined evaluation of growth and nutrient use efficiency, the clones vc865, i182, i144, and gg157 were grouped as drought-tolerant; 1528 and i224 as moderately tolerant; and 1641, 3367, i042, and PL040 as drought-sensitive.

The activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO) was characterized in seeds of the tropical legume Townsville stylo (Stylosanthes humilis) both in vitro (desalted extract of non-dormant seeds) and in vivo (entire dormant seeds). Optimum conditions for maximum in vitro ACO activity in a Trizma-HCl 100 mM buffered medium were: pH 7.0, temperature 32ºC and cofactors and co-substrate at the following concentrations: NaHCO3 30 mM, sodium ascorbate 30 mM and FeSO4 50 µM. Rates of in vitro reaction catalyzed by ACO were shown to be constant within the interval 15-150 minutes from the onset of the reaction. The apparent Km for in vitro ACO, as determined from the non-linear curve fitting to the Michaelis-Menten equation, was 156±8.3 µM ACC with a Vmax 5.4±0.08 mmol (ET) g-1 h-1 on a fresh matter (FM) basis. In vivo (control basal medium: HCl-KOH 10 mM pH 7.0, 30ºC, reaction time 15 hours) apparent Km was 230±27 µM ACC and Vmax 11.9±0.38 mmol (ET) g-1.h-1 on a FM basis. These data suggest that the enzyme exhibits a relatively low affinity for the substrate. The well-known inhibitors of ACO activity, α-aminoisobutyric acid, salicylic and acetylsalicylic acids, n-propylgallate and cobaltous ions, were highly effective in inhibiting ACO activity of Townsville stylo seeds.