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Showing papers by "Universidade Federal de Viçosa published in 2003"


Journal ArticleDOI
TL;DR: In this article, the effects of NaCl stress on the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1), peroxidase (POD:EC 1.11.7), and glutathione reductase (GR: EC1.6.4) were investigated in two cotton cultivars, Guazuncho and Pora, grown in nutrient solution.

1,085 citations


Journal ArticleDOI
TL;DR: In this article, a 50-year long time series of discharge of a tropical river, the Tocantins River at Porto Nacional (175,360 km2), as well as precipitation over this drainage area, during a period where substantial changes in land cover occurred in the basin (1949-1998).

677 citations


Journal ArticleDOI
TL;DR: It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K+ ions in the leaf blades and the accumulation of organic solutes in leaves did not appear to be related to salt tolerance.

422 citations


Journal ArticleDOI
TL;DR: This paper reviewed recent developments in the analysis of this interaction, focusing in particular on how alterations in the structure and functioning of terrestrial ecosystems, through either human land-use practices or global climate change, may affect the future of the earth's climate.
Abstract: While the earth's climate can affect the structure and functioning of terrestrial ecosystems, the process also works in reverse As a result, changes in terrestrial ecosystems may influence climate through both biophysical and biogeochemical processes This two-way link between the physical climate system and the biosphere is under increasing scrutiny We review recent developments in the analysis of this interaction, focusing in particular on how alterations in the structure and functioning of terrestrial ecosystems, through either human land-use practices or global climate change, may affect the future of the earth's climate

349 citations


Book ChapterDOI
01 Jan 2003

323 citations


Journal ArticleDOI
TL;DR: Two hypotheses linked to the question of why there is local variation in arboreal ant species richness in the Brazilian savanna ('cerrado') are tested, finding that there is a positive relationship between Ant species richness and tree species richness, used as a surrogate of heterogeneity.
Abstract: Processes acting on different spatial and temporal scales may influence local species richness. Ant communities are usually described as interactive and therefore determined by local processes. In this paper we tested two hypotheses linked to the question of why there is local variation in arboreal ant species richness in the Brazilian savanna ('cerrado'). The hypotheses are: (i) there is a positive relationship between ant species richness and tree species richness, used as a surrogate of heterogeneity; and (ii) there is a positive relationship between ant species richness and tree density, used as a surrogate of resource availability. Arboreal ants were sampled in two cerrado sites in Brazil using baited pitfall traps and manual sampling, in quadrats of 20 m � 50 m. Ant species richness in each quadrat was used as the response variable in regression tests, using tree species richness and tree density as explanatory variables. Ant species richness responded positively to tree species richness and density. Sampling site also influenced ant species richness, and the relationship between tree density and tree species richness was also positive and significant. Tree species richness may have influenced ant species richness through three processes: (i) increasing the variety of resources and allowing the existence of a higher number of specialist species; (ii) increasing the amount of resources to generalist species; and (iii) some other unmeasured factor may have influenced both ant and tree species richness. Tree density may also have influenced ant species richness through three processes: (i) increasing the amount of resources and allowing a higher ant species richness; (ii) changing habitat conditions and dominance hierarchies in ant communities; and (iii) increasing the area and causing a species-area pattern. Processes acting on larger scales, such as disturbance, altitude and evolutionary histories, as well as sampling effect may have caused the difference between sites.

264 citations


01 Apr 2003
TL;DR: In this paper, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first ∼7.5 years of the mission.
Abstract: [1] Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large wetlands, rivers, and associated floodplains. A clear advantage is the provision of data where traditional gauges are absent. As part of an international program, a complete altimetric analysis of the Amazon Basin is being undertaken. Here, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first ∼7.5 years of the mission. With an initial study group of 230 targets, height variability at many ungauged locations can be observed for 30–50%, the range reflecting the clarity of the variations in lieu of instrument limitations. An assessment of the instrument performance confirms that the minimum river width attainable is ∼1 km in the presence of some inundated floodplain. This constraint does allow observation of the main stem (Solimoes/Amazon) and the larger tributaries, but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval. First-order validation exercises with the deduced 1992–1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters (mean ∼1.1 m rms). Altimetric water levels in the Solimoes and Amazon are particularly well defined with amplitudes <13 m and variations in peak-level timing from May to July. The water-surface gradient of the main stem is found to vary both spatially and temporally, with values ranging from 1.5 cm/km downstream to 4.0 cm/km for more upstream reaches. In agreement with ground-based estimates, the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be ∼0.35 m/s. Overall, the altimetric results demonstrate that the T/P mission is successfully monitoring the transient flood waves of this continental-scale river basin.

244 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the conservation status of Atlantic forest birds in 43 forest fragments ranging in size from 1 to 384 ha in the Vicosa region of southeastern Brazil and compared data from 15 years of field work with historical records from the region, mainly originating from specimens collected by Joao Moojen during the 1930s.
Abstract: : We studied the conservation status of Atlantic forest birds in 43 forest fragments ranging in size from 1 to 384 ha in the Vicosa region of southeastern Brazil. We compared data from 15 years of field work with historical records from the region, mainly originating from specimens collected by Joao Moojen during the 1930s. We used published studies associated with museum data and current field work to assess the decline of forest birds during the last 70 years and to relate their disappearance to forest fragmentation and destruction. At least 28 bird species have become locally extinct, 43 are critically endangered, and 25 are vulnerable, representing 60.7% of the original forest bird community known to exist in the region. Vulnerability to fragmentation differed among guilds, forest strata, and endemicity status. Birds that feed on fruit and seeds, and those that feed on insects, were more threatened than omnivores and carnivores. Nectarivorous species were less threatened than other guilds. Moreover, terrestrial and understory birds or birds using only one forest stratum also were more likely to have been threatened. Finally, Atlantic forest endemics were more likely to have become extinct than nonendemic species. In general, sensitivity to environmental disturbance at the local level was similar to the predicted vulnerability to regional disturbance derived from the literature. Our results indicate that a serious decline of Atlantic forest birds is underway and that many other species of birds, not previously recognized as threatened, are of conservation concern. Resumen: Estudiamos el estado de conservacion de aves de bosque atlantico en 43 fragmentos de 1 a 384 ha en la Region Vicosa, al sureste de Brasil. Comparamos datos de 15 anos de trabajo de campo con registros historicos de la region, principalmente de especimenes colectados por Joao Moojen durante la decada de los anos 30. Utilizamos estudios publicados asociados con datos de museo y de trabajo de campo reciente para analizar la disminuicion de aves de bosque durante los ultimos 70 anos y para relacionar su desaparicion con la fragmentacion y destruccion del bosque. Se han extinguido por lo menos 28 especies de aves localmente, 43 estan criticamente en peligro y 25 son vulnerables, lo cual representa el 60,7% de la comunidad de aves de bosque conocida para la region. La vulnerabilidad a la fragmentacion fue diferente entre gremios, estratos de bosque y estado de endemismo. Las aves que se alimentan de frutos y semillas y aquellas que se alimentan de insectos estan mas amenazadas que las omnivoras y carnivoras. Las especies nectarivoras estan menos amenazadas que otros gremios. Mas aun, las aves terrestres y de sotobosque o las que utilizan solo un estrato del bosque tambien tienen mayor probabilidad de estar amenazadas. Finalmente, las aves endemicas al bosque atlantico tienen mayor probabilidad de extincion que las no endemicas. En general, la sensibilidad a la perturbacion ambiental a nivel local fue similar a la vulnerabilidad a la perturbacion regional predicha, derivada de la bibliografia. Nuestros resultados indican que existe una seria declinacion de aves de bosque atlantico y que muchas otras especies de aves, no reconocidas como amenazadas previamente, son de interes para la conservacion.

182 citations


Journal ArticleDOI
TL;DR: Results from insecticide bioassays with synergists suggested a major involvement of esterase as the cypermethrin resistance mechanism, while no clear result was obtained for chlorpyrifos-methyl, which provides support for target site resistance to pyrethroids in the DDT and pyrethroid resistant population used in this study.

179 citations


Journal ArticleDOI
TL;DR: The results indicate the existence of a high degree of pre-existing genetic diversity among tomato-infecting begomoviruses in Brazil and suggest that these viruses have emerged after being transferred from natural hosts to tomatoes, due to the introduction into Brazil of a novel polyfagous biotype of the whitefly vector.
Abstract: Tomato-infecting begomoviruses have been reported throughout Brazil since the introduction of the B biotype of Bemisia tabaci. Here, we report a large scale survey on the distribution and genetic diversity of tomato-infecting begomoviruses. Tomato samples with typical begomovirus symptoms were collected in seven different states, comprising the major tomato growing areas of the country. Viruses were detected by polymerase chain reaction (PCR) using universal primers for the genus Begomovirus. PCR-amplified fragments were cloned and sequenced. Based on sequence comparisons and phylogenetic analyses, at least seven previously undescribed species of begomoviruses were found. Four of the new viruses were found exclusively in the Southeastern states, two exclusively in the Northeastern states, and one was found in both regions. Sequence comparisons reveal strong evidence of recombination among the Brazilian begomoviruses. Together, the results indicate the existence of a high degree of pre-existing genetic diversity among tomato-infecting begomoviruses in Brazil and suggest that these viruses have emerged after being transferred from natural hosts to tomatoes, due to the introduction into Brazil of a novel polyfagous biotype of the whitefly vector.

159 citations


Journal ArticleDOI
TL;DR: In this article, the performance of the adsorption complex of heavy metal cations was investigated on representative Brazilian soils and the simultaneous competitive adaption on the mineral matrix of Cr, Ni, Cu, Zn, Cd and Pb was determined.

Journal ArticleDOI
TL;DR: Tolerance to soil drought of two field-grown clones of Coffea canephora was compared and clone 120 was better able to postpone dehydration and to maintain whole-tree photosynthesis and it is proposed that these features should decisively contribute to buffer its productivity in drought-prone areas.

Journal ArticleDOI
TL;DR: This is the first report of a disease resistance gene identified in Eucalyptus, and one of the few examples of the involvement of a major gene in a non-coevolved pathosystem.
Abstract: Rust is one of the most-damaging eucalypt diseases in Brazil and is considered a potential threat to eucalypt plantations worldwide. To determine the mode of inheritance of resistance in the Eucalyptus grandis—Puccinia psidii pathosystem, ten full-sib families, generated from crosses between susceptible and resistant trees, were inoculated with a single-pustule isolate of the pathogen and rust severity was scored. The observed segregation ratios in segregating families suggested major gene control of rust resistance, although clearly incomplete penetrance, variable expressivity and minor genes are also involved in the global rust-resistance response. To identify markers linked to the resistance locus, screening of RAPD polymorphisms was conducted using bulked segregant analysis in a large full-sib family. A linkage group was built around the Ppr1 gene (P. psidii resistance gene 1) encompassing six RAPD markers, with a genetic window spanning 5 cM with the two most-closely linked flanking markers. Besides these two flanking markers, RAPD marker AT9/917 co-segregated with Ppr1 without a single recombinant in 994 meioses. This tightly linked marker should prove useful for marker-assisted introgression and will provide an initial lead for a positional cloning effort of this resistance allele. This is the first report of a disease resistance gene identified in Eucalyptus, and one of the few examples of the involvement of a major gene in a non-coevolved pathosystem.

Journal ArticleDOI
TL;DR: Xyloglucans and galactomannans are examples of hemicelluloses that can be accumulated in seeds of many plants, being extensively studied and used for industrial applications as discussed by the authors.

Journal ArticleDOI
TL;DR: The data indicate the importance of food components in preventing genetic damage induced by chemical mutagens, and also reinforce the role of toxicogenetic techniques in protecting human health.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the effects of different tillage systems on chemical and physical attributes of a soil, in a long-term experiment installed in 1985, in which samples were collected after the culture of maize (crop 2001/02), at depths of 0-5, 5-10 and 10-20 cm.
Abstract: Different tillage systems cause changes in the chemical, physical and biological attributes of a soil, requiring modifications in the requirements of fertilization and liming. The aim of this work was to evaluate the effects of tillage systems on chemical and physical attributes of a soil, in a long-term experiment installed in 1985. Since then, the soil has been cultivated with annual cultures and submitted to six tillage systems: no-tillage (SD), disc plow (AD), moldboard plow (AA), heavy disc harrow (GP), heavy disc harrow + moldboard plow (GP + AA) and heavy disc harrow + disc plow (GP + AD). The experimental design was in completely randomized blocks with four replications. Samplings were collected after the culture of maize (crop 2001/02), at depths of 0-5, 5-10 and 10-20 cm. Soil samples were submitted to chemical and physical analyses and the averages compared by the Tukey test. The tillage systems affected the chemical and physical attributes of a soil distinctly. Greatest differences were observed between the SD treatment and the others. SD showed higher bulk density values than the other treatments, in the average of the three depths. In the 0-5 cm layer of SD, increments of the medium values of organic matter, pH, cation-exchange capacity, exchangeable calcium, exchangeable magnesium, exchangeable potassium and phosphorus available were observed; in relation to the other depths. The aluminum value was smaller in the SD treatment in the 0-5 cm layer than the others; at the depth 10-20 cm, this value was higher than the treatments AD, GP and GP + AA. Treatments AD, GP, GP + AD and GP + AA showed higher values of exchangeable potassium than the treatments SD and AA, at the depth 0-5 cm. Treatment SD presented values of available phosphorus superior to the other treatments, at the depth 0-5 cm and in the average of the three depths.

Journal ArticleDOI
TL;DR: Molar concentrations should be used to carbohydrate concentrations reference because it isolates the osmotic variable influence that acts concomitantly with the nutritional variable.

Journal ArticleDOI
TL;DR: In this article, a reducão of adsorcao/precipitacao de fosfato (A/PP) pela adicao de acidos orgânicos: acido citrico (AC), oxalico (AO), salicilico (AS), acidos humicos (AH), and acidos organicos (AOG) was evaluated in Latossolos.
Abstract: A materia orgânica pode diminuir a adsorcao/precipitacao de fosfato (A/PP) pela liberacao de acidos orgânicos, que competem pelos sitios de adsorcao, ou pela formacao de compostos com o fosfato na solucao do solo e, ou, formacao de complexos com Al e Fe, reduzindo a A/PP. O objetivo deste trabalho foi avaliar a reducao na A/PP em Latossolos, pela adicao de acidos orgânicos: acido citrico (AC), oxalico (AO), salicilico (AS) - e de acidos humicos (AH). Foram utilizadas amostras de um Latossolo Vermelho textura muito argilosa - (LV) e um Latossolo Vermelho-Amarelo textura franco-argilo-arenosa - (LVA). Amostras de 2,5 cm3 de TFSA dos solos foram colocadas em erlenmeyer onde foram adicionados: fosforo (K2HPO4) e, ou, acidos orgânicos ou humicos, de acordo com a forma de aplicacao (fosfato antes, junto e depois da aplicacao do acido), nas doses da relacao molar acido orgânico/P variando de 0 a 2:1. As doses dos acidos humicos variaram de 0 a 89,28 mg cm-3, equivalendo a adubacao orgânica de 0 a 40 t ha-1 de material orgânico. O efeito dos acidos orgânicos/acidos humicos na reducao da A/PP nos dois solos seguiu a seguinte ordem: AC > AO > AH > AS. A forma de adicao dos acidos influenciou a A/PP em ambos os solos. No LV, a aplicacao de fosfato e acidos orgânicos ou acidos humicos juntos (FJA) causou a maior reducao na A/PP, indicando que deve ter ocorrido a ligacao entre fosfato e acidos. No LVA, a aplicacao de fosfato depois dos acidos orgânicos ou acidos humicos (FDA) causou a maior reducao na A/PP, indicando ter ocorrido bloqueio dos sitios de adsorcao pelos acidos.

Journal ArticleDOI
TL;DR: In this article, the authors developed and evaluated an algorithm at simplified lighting conditions for identifying damaged maize plants by the fall armyworm using digital color images, which correctly classified 94·72% of the images.

Journal ArticleDOI
TL;DR: In this article, an experiment was carried out to study the growth of Eucalyptus grandis seedlings produced in different sized tubes and N-P-K fertilization, and four sizes of hard plastic tubes at the volumes of 50, 110, 200 and 280 cm3 were used as containers.
Abstract: An experiment was carried out to study the growth of Eucalyptus grandis seedlings produced in different sized tubes and N-P-K fertilization. A mixture of 80% organic compound (CO) and 20% charcoal powder fertilized with and without N, P and K was used as substrate. Four sizes of hard plastic tubes at the volumes of 50, 110, 200 and 280 cm3 were used as containers. The tube volumes must be considered for producing Eucalyptus grandis seedlings. Although the highest growths occurred in the larger tubes, these tubes should not be used because the seedling heights far surpass the ones considered as technically optimum for planting, and have a higher production cost. At 60 days of age, the seedlings are still small and quite tender, and do not present the hardness appropriate to field planting. At 120 days after sowing, the restriction to root growth and seedling height is affected even in the larger tubes, thus this is not the indicated age. The 110 cm3 volume tube must be considered for 90-day old seedlings.

Journal ArticleDOI
TL;DR: Silicon may offer a viable method to control sheath blight in areas where soil is deficient in Si and the highest relative lesion height on the main tiller decreased by 37%, 40%, 52% and 24%, respectively.

Journal ArticleDOI
TL;DR: In this paper, the effect of maize production systems under organic and mineral fertilization on total organic carbon (TOC) and total nitrogen (TN) stocks and on organic carbon pools (C) in an Acrisol was evaluated.
Abstract: Soil organic matter and its different pools have key importance in nutrient availability, soil aggregation, and in the greenhouse gas fluxes between the earth surface and the atmosphere. The objectives of this study were: a) to evaluate the effect of maize production systems under organic and mineral fertilization on total organic carbon (TOC) and total nitrogen (TN) stocks and on organic carbon pools (C) in an Acrisol; and b) to estimate the contribution of these systems in the atmospheric CO2 sequestration or emission. The production systems included two levels of organic compost: level 0 (control) and level 1 (40 m3 ha-1); and three levels of mineral fertilizer (0, 1 and 2), which correspond to 0,250 (AM1), and 500 kg ha-1 (AM2) of the 4-14-8 formula. Organic and mineral fertilizer were combined and applied during 16 years. As a reference of the steady state, soil samples were collected from an adjacent area of the same soil type, under secondary Atlantic Forest (AF). Where organic compost was added, the production systems presented higher organic C and N soil storage, light fraction carbon (CLF) and labile carbon (CL) than production systems without fertilization or with mineral fertilizer only. This confirms the importance of organic fertilizer utilization as a management strategy to improve soil quality. However, the soil under AF showed higher values of organic C and N storage and carbon pools than soils under production systems. Due to their higher sensitivity, the stocks of the CLF and CL were more severely decreased than the TOC stocks and thus, may be used as indicators of the anthropogenic impact or the influence of management alterations on the soil organic matter.

Journal ArticleDOI
TL;DR: In this article, the effects of adding emulsifying vegetable oil to the pesticide emulsion and using low drift nozzles on droplet spectrum formation and, consequently, on the drift potential of fan spray nozzle were evaluated.
Abstract: Pesticide spray drift is a major problem in agriculture today. Among the factors influencing drift, droplet size is of paramount importance. Thus, this work aimed to evaluate the effects of adding emulsifying vegetable oil to the pesticide emulsion and using low drift nozzles on droplet spectrum formation and, consequently, on the drift potential of fan spray nozzles. Droplet distribution was measured under controlled atmosphere, using a real time laser particle size analyzer. The droplets were generated with standard nozzles, with and without the addition of adjuvants, and with low drift nozzles, with the operating pressure ranging from 200 to 400 kPa. Also, drift was evaluated in the field, using artificial targets placed outside the application area, where droplet counting was accomplished. The results showed that both the addition of vegetable oil to the pesticide emulsion and the use of low drift nozzles altered droplet size spectra, increasing the diameter of the drops and reducing the percentage of drops subject to wind action being, thus, effective factors in drift reduction.

Journal ArticleDOI
TL;DR: In this article, the authors quantify litterfall and litter decomposition in an agroforestry system in Vicosa, Minas Gerais and compare litter production with the results obtained in semideciduous forests in Southeastern Brazil.
Abstract: This study aimed to quantify litterfall and litter decomposition in an agroforestry system in Vicosa, Minas Gerais and to compare litter production with the results obtained in semideciduous forests in Southeastern Brazil. Twenty wooden litter traps of 0.5 x 0.5 m with nylon screen bottoms and 1.0 mm 2 mesh were used, placed 10 cm above the surface of the soil. The collections were performed monthly from September 2000 to August 2001. The material deposited in the traps, under laboratory conditions, was sorted out in the fractions leaves, branches (up to 2.0 cm of diameter) and reproductive material, - dried to 70 oC and weighed in a precision scale. The annual litter production was estimated in 10165.13 kg/ha (67.46% leaves, 19.87% reproductive material and 12.67% branches). The largest production values occurred at the end of the dry season, reaching a maximum value in September. The decomposition coefficient (K) was 1.17 and the time needed for the disappearance of 50% of the litter was estimated in 215 days.

Journal ArticleDOI
TL;DR: The administration of nematophagous fungi to animals has been considered an alternative in gastrointestinal helminthiasis prophylaxis and several fungi formulations have been evaluated, but there is so far no commercial product available.
Abstract: Biological control is a non-chemical alternative method with its main goal to reduce the amount of parasite population using natural antagonists. The administration of nematophagous fungi to animals has been considered an alternative in gastrointestinal helminthiasis prophylaxis. The nematophagous fungi produce trap-shaped structures, which are responsible for capturing and destroying the free-living stages of nematodes. The genera Arthrobotrys, Duddingtonia and Monacrosporium has been shown efficacy in laboratory and field experiments against cattle, equine, ovine and swine parasites. Several fungi formulations have been evaluated, but there is so far no commercial product available. The association of research groups with industry could improve the successful implementation of this control method.

Journal ArticleDOI
TL;DR: In this paper, the seasonal effects of the surface albedo change after a tropical deforestation and its influence on the seasonal pattern of precipitation in Amazonia were studied, and the results of the climate simulation study of Costa and Foley were used to represent the precipitation changes in a scenario where all tropical forest was replaced by pasture.
Abstract: This work studies the seasonal effects of the surface albedo change after a tropical deforestation and its influence on the seasonal pattern of precipitation in Amazonia. Results of the climate simulation study of Costa and Foley are used to represent the precipitation changes in a scenario where all tropical forest was replaced by pasture. The simulated forest and pasture albedo are compared to both the forest and pasture albedos observed during the Anglo-Brazilian Amazonian Climate Observation Study (ABRACOS) project. The surface albedo measurements provided verification that both forest and pasture albedo show seasonal variability, with the forest albedos higher in the dry period (June–November) and lower values in the rainy period (December–May), while the pasture albedo decreases in the dry season. Most of the characteristics of the observed differences in albedo are present in the simulated albedo too, which is in part due to the ability of the land surface parameterization to represent veg...

Journal ArticleDOI
TL;DR: Investigating the vertical distribution of AMF spores in Oxisols under agroforestry and monocultural (unshaded) coffee systems in on-farm experiments (Brazil) found greater numbers of spores in the deeper soil layers may be explained by greater amounts of roots and may be an indicator of greater incidence of mycorrhiza in agroForestry than in monoccultural coffee systems.
Abstract: Deep-rooting trees in agroforestry systems may promote distribution of spores of arbuscular mycorrhizal fungi (AMF) at deeper soil levels. We investigated the vertical distribution of AMF spores in Oxisols under agroforestry and monocultural (unshaded) coffee systems in on-farm experiments (Brazil). The number of AMF spores was considered as an indicator of mycorrhiza incidence in soil. Spores were extracted from 0–1, 2–3, 5–7.5, 10–15, 20–30, 40–60 cm soil-depths in agroforestry and monocultural coffee systems, of three different age groups (young, medium-aged and old), using centrifugation methods, and counted. Fine roots were collected and dry-weighed from 0–30 cm in young and old systems and from several depths in medium-aged systems. Soils were characterised with respect to texture, pH, organic matter, calcium, magnesium, phosphorus and potassium. Agroforestry had a higher percentage of spores (12–21% of the total number of spores) and roots (on average 1.5 g L−1 soil) in deeper layers (20–60 cm), and a lower percentage (79–88%) closer to the surface (0–15 cm) than the monocultural fields (respectively 3–12%, 0.6 g L−1 soil and 88–97%). Greater numbers of spores in the deeper soil layers may be explained by greater amounts of roots and may be an indicator of greater incidence of mycorrhiza in agroforestry than in monocultural coffee systems. Greater mycorrhizal incidence at deeper soil layers in the agroforestry system may change the dynamics of phosphorus cycling in soil, making this nutrient more available to plants.

Journal ArticleDOI
TL;DR: Testing 500 rhizobacteria isolated from tomato rhizosphere for their ability to induce systemic resistance against Pseudomonas syring ae pv, 28 of them did reduce infection to less than 40% and all 28 colonized roots according to the described bioassay.
Abstract: The ability to colonize roots is a sine qua non condition for a rhizobacteria to be considered a true plant growth-promoting rhizobacteria (PGPR). A simple screening method to detect such a potential ability of PGPR is described. Tomato seeds were surface sterilized for 30 s in 50% ethanol and this is followed by 3–5min dipping in 2% NaClO. They were then washed three times in sterile water, left immersed in a propagules suspension of the rhizobacteria for 24 h, and transferred onto sterile 0.8% water-agar in tubes. The young, developing root system shows a tendency to grow downwards in the agar-gel column. When the rhizobacteria has a potential ability to colonize roots it is possible to visualize, by transparency, bacterial growth (turbid, milky and narrow zone) along and around roots. Testing 500 rhizobacteria isolated from tomato rhizosphere for their ability to induce systemic resistance against Pseudomonas syringae pv. tomato ,2 8 of them did reduce infection to less than 40% and all 28 colonized roots according to the described bioassay. Therefore the bioassay may turn into an important auxiliary tool for helping in selecting rhizobacteria with PGPR potentiality.

Journal ArticleDOI
TL;DR: The results of biochemical in vitro studies measuring the activity of detoxification enzymes (esterases and glutathion S‐transferases) in conjunction with canonical correlation analysis suggest a major involvement of enhanced conjugation by glutathione S‐ transferases in pyrethroid resistance and, in the case of cypermethrin resistance, enhanced phosphotriesterase activity.
Abstract: Insecticide resistance patterns among 16 Brazilian populations of the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), were recognized by surveying resistance to three organophosphates (chlorpyrifos-methyl, malathion, and pirimiphos-methyl) and three pyrethroids (cypermethrin, deltamethrin, and permethrin). Two population clusters were obtained: one with three populations (Braganca Paulista, Cristalina, and Nova Andradina) showing low frequency of cypermethrin resistance (13-36%) and negligible frequency of deltamethrin resistance (2-9%); and another with six populations (Campos dos Goytacazes, Ivinhema, Patos de Minas, Penapolis, Uberlândia, and Venda Nova) showing low to negligible levels of pyrethroid resistance (0-23%). The remaining seven populations, including a susceptible, and a DDT- and pyrethroid-resistant reference populations (Sete Lagoas and Jacarezinho, respectively), were significantly different from each other and from the two recognized clusters. In contrast with pyrethroid resistance, organophosphate resistance was negligible except for chlorpyrifos-methyl in two populations (Fatima do Sul and Penapolis). There was no correlation between geographic distance and the Mahalanobis distance estimated from the resistance pattern ordination of the populations by canonical variate analysis, suggesting local selection and/or broad dispersal of resistant populations by grain trade. The results of biochemical in vitro studies measuring the activity of detoxification enzymes (esterases and glutathion S-transferases) in conjunction with canonical correlation analysis suggest a major involvement of enhanced conjugation by glutathione S-transferases (> 2-fold increase) in pyrethroid resistance and, in the case of cypermethrin resistance, enhanced phosphotriesterase activity.

Journal ArticleDOI
TL;DR: O objetivo deste trabalho foi estimar as quantidades de nutrientes reciclados por cinco especies vegetais utilizadas como culturas de cobertura do solo e que podem retornar ao solo pela mineralizacao da biomassa.
Abstract: Resumo – O objetivo deste trabalho foi estimar as quantidades de nutrientes reciclados por cinco especies vegetais utilizadas como culturas de cobertura do solo e que podem retornar ao solo pela mineralizacao da biomassa. Foram coletadas de varios experimentos amostras da materia verde de aveia-preta (Avena strigosa Schreb), mucuna-preta (Stizolobium aterrimum Piper & Tracy), guandu (Cajanus cajan (L.) Millsp), tremoco (Lupinus albus L. e L. angustifolius L.) e ervilhaca (Vicia sativa L.). Foi estimado o rendimento de materia seca e determinados os teores de N, P, K, Ca, Mg, Mn, Zn, Cu, e, a partir dessas concentracoes, foram calculadas a media observada, a media estimada e o intervalo de confianca a 95% para cada nutriente dentro de cada classe de rendimento de materia seca, em cada especie vegetal. Os dados foram tabulados dentro de intervalos de classe de rendimento de materia seca e apresentadas as quantidades estimadas de nutrientes minerais. Foram ajustadas equacoes para estimar as quantidades desses nutrientes. A aveia-preta e a ervilhaca reciclam grande quantidade de K, e a ervilhaca, a mucuna-preta, o tremoco e o guandu reciclam grande quantidade de N. Todas as especies reciclam quantidades apreciaveis de Ca, Mg e micronutrientes, porem baixas quantidades de P. A rotacao de culturas e um meio de implementar com sucesso o aumento das areas de lavoura em semeadura direta. Termos para indexacao: plantas de protecao, reciclagem de nutriente, mineralizacao, rotacao de culturas. Mineral nutrients in the shoot biomass of soil cover crops