Liming effects on growth of native woody species from Brazilian Savannah

The liming effects on the growth of fifteen woody species of Brazil were evaluated under glasshouse conditions. The species used belong to different ecologic groups, namely: pioneer, secondary and climax trees. The soil treatments consisted in the absence of liming (-LIM) and liming sufficient to reach soil pH 6.0 (+LIM). In general, the pioneer and secondary species presented higher responses in total dry matter production (TDM) to soil liming, whereas the TDM of the climax species were not affected by the soil treatments. Thus, the ranking of species in relation to soil acidity tolerance ranged from highly sensitive to highly tolerant. The pioneer and secondary species growing in limed soil (+LIM) showed higher calcium (Ca), magnesium (Mg) and phosphorus (P) contents, and, at the same time lower Ca, Mg utilization efficiency (CaUE and MgUE respectively), whereas the P utilization (PUE) was higher. In contrast, the Ca, Mg and P content in the climax species were only slightly affected by the soil liming. In general the climax species were less efficient in the CaUE and MgUE than the pioneer and secondary species.

Diallel analysis for grain yield and mineral absorption rate of soybeans grown in acid brazilian savannah soil

High available aluminium and low levels of calcium below the ploughed zone of the soil are limiting factors for agricultural sustainability in the Brazilian Cerrados (Savannahs). The mineral stresses compound with dry spells effect by preventing deep root growth of cultivated plants and causes yield instability. The mode of inheritance for grain yield and mineral absorption ratio of a diallel cross in soybeans [Glycine max (L.) Merrill] grown in high and low Al areas was identified. Differences among the genotypes for grain yield were more evident in the high Al, by grouping tolerant and non-tolerant genotypes for their respective arrays in the hybrids. A large proportion of genetic variance was additive for grain yield and mineral absorption ratio in both environments. High heritability values suggest that soybeans can be improved by crosses among Al-tolerant genotypes, using modified pedigree, early generation and recurrent selection schemes.

Symbiotic effectiveness and ecological characterization of indigenous Rhizobium loti populations in Uruguay

The objectives of this work were to describe the distribution, density and seasonal variation of the indigenous populations of Rhizobium loti in different Uruguayan soils and to determine the symbiotic effectiveness and stress tolerance factors of different isolates, both with the aim of obtaining selected strains to re-introduce as inoculants in Lotus pastures. R. loti was present in ten soils studied and their densities varied from year to year and within each soil. All the isolates nodulated Lotus corniculatus effectively. The nodules in Lotus pedunculatus and Lotus subbiflorus were small, red on the surface and ineffective in nitrogen fixation. The study of 50 isolates from the ten soils showed high variability in their symbiotic efficiency and tolerance to pH. The indigenous population was acid tolerant in culture medium (pH 4.5), 83% of them could grow at pH 4.5 in 3 days. This work showed that there was a great diversity between the strains of R. loti isolated from Uruguayan soils and supports the importance of selecting among them the most efficient and resistant strains to be included in the inoculants.

Isolation of a cotton NADP(H) oxidase homologue induced by drought stress

The aim of this study was to identify and isolate genes that are differentially expressed in four selected cotton (Gossypium hirsutum L.) genotypes contrasting according to their tolerance to water deficit. The genotypes studied were Siokra L-23, Stoneville 506, CS 50 and T-1521. Physiological, morphological and developmental changes that confer drought tolerance in plants must have a molecular genetic basis. To identify and isolate the genes, the mRNA Differential Display (DD) technique was used. Messenger RNAs differentially expressed during water deficit were identified, isolated, cloned and sequenced. The cloned transcript A12B15-5, a NADP(H) oxidase homologue, was up regulated only during the water deficit stress and only in Siokra L-23, a drought tolerant genotype. Ribonuclease protection assay confirmed that transcription.

Physiological and morphological responces of Brachiaria spp. to flooding

The physiological and morphological responses of the forage grasses Brachiaria brizantha cv. Marandu, B. decumbens and B. humidicola were compared for plants grown in pots under flooding and well-drained conditions for 14 days. Flooding reduced specific leaf area and biomass allocation to roots in all species and enhanced leaf senescence in B. brizantha and B. decumbens. Relative growth rate was reduced by flooding in B. brizantha and B. decumbens, but not in B. humidicola.Leaf elongation rate was unaffected by flooding in B. decumbens and B. humidicola, but declined in B. brizantha since the first day of flooding. Net photosynthesis and leaf chlorophyll content were reduced by flooding in B. brizantha; however, no flooding effect could be detected in the other two species. For all species, there was a close relationship between net photosynthesis and stomatal conductance under flooding. These results show that the studied species have distinct degrees of tolerance to flood, B. brizantha is intolerant, B. decumbens is moderately tolerant and B. humidicola is tolerant. Because leaf elongation rate was immediately depressed by flooding only in B. brizantha, this measurement could be appropriate as an early detection mechanism for relative flood tolerance in Brachiaria spp.

Flooding tolerance and cell wall alterations in maize mesocotyl during hypoxia

This research aimed to characterize the tolerance to flooding and alterations in pectic and hemicellulose fractions from mesocotyl of maize tolerant to flooding when submitted to hypoxia. In order to characterize tolerance seeds from maize cultivars Saracura BRS-4154 and BR 107 tolerant and sensitive to low oxygen levels, respectively, were set to germinate. Plantlet survival was evaluated during five days after having been submitted to hypoxia. After fractionation with ammonium oxalate 0.5% (w/v) and KOH 2M and 4M, Saracura BRS-4154 cell wall was obtained from mesocotyl segments with different damage intensities caused by oxygen deficiency exposure. The cell wall fractions were analyzed by gel filtration and gas chromatography, and also by Infrared Spectrum with Fourrier Transformation (FTIR). The hypoxia period lasting three days or longer caused cell lysis and in advanced stages plant death. The gelic profile from pectic, hemicellulose 2M and 4M fractions from samples with translucid and constriction zone showed the appearance of low molecular weight compounds, similar to glucose. The main neutral sugars in pectic and hemicellulose fractions were arabinose, xilose and mannose. The FTIR spectrum showed a gradual decrease in pectic substances from mesocotyl with normal to translucid and constriction appearance respectively.

Tolerance to flooding in five Brachiaria brizantha accessions

Some physiological and morphological responses of five Brachiaria brizantha accessions (BRA000591 cultivar Marandu, BRA003441, BRA002844, BRA004308 and BRA004391) were compared for plants grown in pots under flooding and well-drained conditions for 14 days. Flooding caused a significant reduction in leaf dry mass production in all accessions, but, for root biomass, no differences between treatments could be detected in BRA003441 and BRA004391. No adventitious root production was observed in flooded BRA003441; all other accessions produced adventitious roots when flooded. Relative growth rate was reduced by flooding only in BRA000591 and BRA004308. Leaf elongation rate was reduced by flooding in all accessions, however, more severely in BRA003441. Net photosynthesis was reduced by flooding in all accessions, but with less intensity in BRA004391. For all accessions, there was a close relationship between net photosynthesis and stomatal conductance under flooding. The five accessions tested differed in tolerance to flooding. BRA004391 was the most tolerant. Accession BRA003441 was the most sensitive, followed by BRA000591 cultivar Marandu. Accessions BRA002844 and BRA004308 were classified as intermediate in flooding tolerance.

Genetic analysis of aluminum tolerance in Brazilian barleys

Aluminum (Al) toxicity is a major factor limiting barley growth in acid soils, and genotypes with adequate level of tolerance are needed for improving barley adaptation in Brazil. To study the inheritance of Al tolerance in Brazilian barleys, cultivars Antarctica 1, BR 1 and FM 404 were crossed to sensitive Kearney and PFC 8026, and intercrossed. Parental, F1, F2 and F6 generations were grown in nutrient solution containing 0.03, 0.05 and 0.07 mM of Al and classified for tolerance by the root tip hematoxylin staining assay. Tolerant by sensitive F2 progenies segregated three tolerant to one sensitive, fitting the 3:1 ratio expected for a single gene. The F6 populations segregated one tolerant to one sensitive also fitting a monogenic ratio. The F2 seedlings from crosses among tolerant genotypes scored the same as the parents. Since the population size used would allow detection of recombination as low as 7%, the complete absence of Al sensitive recombinants suggests that tolerance in these cultivars is most probably, controlled by the same gene. Thus, the potential for improving Al tolerance through recombination of these genotypes is very low and different gene sources should be evaluated.

Sweet orange trees grafted on selected rootstocks fertilized with nitrogen, phosphorus and potassium

The majority of citrus trees in Brazil are grafted on 'Rangpur lime' (Citrus limonia Osb.) rootstock. Despite its good horticultural performance, search for disease tolerant rootstock varieties to improve yield and longevity of citrus groves has increased. The objective of this work was to evaluate yield efficiency of sweet oranges on different rootstocks fertilized with N, P, and potassium. Tree growth was affected by rootstock varieties; trees on 'Swingle' citrumelo [Poncirus trifoliata (L.) Raf. × C. paradisi Macf.] presented the smallest canopy (13.3 m³ in the fifth year after tree planting) compared to those on 'Rangpur lime' and 'Cleopatra' mandarin [C. reshni (Hayata) hort. ex Tanaka] grown on the same grove. Although it was observed an overall positive relationship between canopy volume and fruit yield (R² = 0.95**), yield efficiency (kg m-3) was affected by rootstocks, which demonstrated 'Rangpur lime' superiority in relation to Cleopatra. Growth of citrus trees younger than 5-yr-old might be improved by K fertilization rates greater than currently recommended in Brazil, in soils with low K and subjected to nutrient leaching losses.

Spider mites associated to soybean in Rio Grande do Sul, Brazil

The objective of this work was to study the occurrence and geographic distribution of phytophagous mites associated to soybean in Rio Grande do Sul, Brazil. Samplings were performed from January to May 2005 on genetically modified soybean (glyphosate-tolerant) crops, in 27 municipalities of six regions - Alto Vale do Uruguai, Campanha, Depressão Central, Planalto Médio, Missões and Serra do Sudeste. Five phytophagous mite species belonging to the family Tetranychidae - Mononychellus planki, Tetranychus desertorum, T. gigas, T. ludeni and T. urticae - occurred in 21, 12, 5, 3 and 14 municipalities, respectively. A map of Rio Grande do Sul with the geographic distribution of each species is presented, as well as an illustrated dichotomous key to help the identification of the spider mites found.

Low-P tolerance mechanisms and differential gene expression in contrasting wheat genotypes

The objectives of this study were to determine low-P tolerance mechanisms in contrasting wheat genotypes and to evaluate the association of these mechanisms to differential gene expression. Wheat seedlings of cultivars Toropi (tolerant to low-P availability) and Anahuac (sensitive) were evaluated. Seedlings were hydroponically grown in the absence or presence of P (1.0 mmol L-1) during three different time periods: 24, 120 and 240 hours. Free phosphate (Pi) and total P contents were measured in shoots and roots. The experiment's design was in randomized blocks with three replicates, each formed by ten plants. The relative expression of genes encoding the malate transporter TaALMT1 and the transcription factor PTF1 was evaluated. Phosphorus starvation beyond ten days increased the expression of TaALMT1 only in 'Toropi'. PTF1's expression was early induced in both genotypes under P starvation, but remained significant after ten days only in 'Toropi'. Shoot Pi concentration in 'Toropi' was independent from P availability; under starvation, 'Toropi' favored the maintenance of shoot Pi concentration. The low-P tolerance of Toropi cultivar at initial growth stages is mainly due to its ability to maintain constant the Pi shoot level.

Economic analysis of an agrosilvipastoral system for a mountainous area in Zona da Mata Mineira, Brazil

The objective of this work was to evaluate the economic viability of an agrosilvipastoral system developed for Zona da Mata mountainous areas in Minas Gerais state, Brazil, as well as to compare different options for wood (Eucalyptus grandis and Acacia mangium) commercialization of the second thinning. The data were obtained from a 10 year-old agrosilvipastoral system established in four hectares at Embrapa Gado de Leite station in Coronel Pacheco, MG, Brazil. As evaluation criteria for the economic viability analysis, the adopted methods were the net present value (NPV) and the internal rate of return (IRR), both calculated at 6% interest rate. Despite the small difference, adding value to forest products increased the attractiveness of the proposed system. Considered separately, the agricultural activity was impracticable, whereas the forestry and livestock activities were independently viable. The studied system seems to be equally tolerant to price variations for forest and livestock products, as well as strongly tolerant to variations in production costs.

Salt tolerance and regulation of gas exchange and hormonal homeostasis by auxin-priming in wheat

The objective of this work was to assess the regulatory effects of auxin-priming on gas exchange and hormonal homeostasis in spring wheat subjected to saline conditions. Seeds of MH-97 (salt-intolerant) and Inqlab-91 (salt-tolerant) cultivars were subjected to 11 priming treatments (three hormones x three concentrations + two controls) and evaluated under saline (15 dS m-1) and nonsaline (2.84 dS m-1) conditions. The priming treatments consisted of: 5.71, 8.56, and 11.42 × 10-4 mol L-1 indoleacetic acid; 4.92, 7.38, and 9.84 × 10-4 mol L-1 indolebutyric acid; 4.89, 7.34, and 9.79 × 10-4 mol L-1 tryptophan; and a control with hydroprimed seeds. A negative control with nonprimed seeds was also evaluated. All priming agents diminished the effects of salinity on endogenous abscisic acid concentration in the salt-intolerant cultivar. Grain yield was positively correlated with net CO2 assimilation rate and endogenous indoleacetic acid concentration, and it was negatively correlated with abscisic acid and free polyamine concentrations. In general, the priming treatment with tryptophan at 4.89 × 10-4 mol L-1 was the most effective in minimizing yield losses and reductions in net CO2 assimilation rate, under salt stress conditions. Hormonal homeostasis increases net CO2 assimilation rate and confers tolerance to salinity on spring wheat.

Tolerance to preharvest sprouting and yield of wheat genotypes from different breeding programs

Abstract:The objective of this work was to characterize the performance of elite wheat genotypes from different Brazilian breeding programs for traits associated with grain yield and preharvest sprouting. The study was conducted in 2010 and 2011 in the municipality of Capão do Leão, in the state of Rio Grande do Sul, Brazil, in a randomized complete block design with three replicates. Thirty-three wheat genotypes were evaluated for traits related to preharvest sprouting and grain yield. The estimate of genetic distance was used to predict potential combinations for selection of plants with high grain yield and tolerance to preharvest sprouting. The combined analysis of sprouted grains and falling number shows that the TBIO Alvorada, TBIO Mestre, Frontana, Fundacep Raízes, Fundacep Cristalino, and BRS Guamirim genotypes are tolerant to preharvest sprouting. Combinations of TBIO Alvorada and TBIO Mestre with Fundacep Cristalino show high potential for recovering superior genotypes for high grain yield and tolerance to preharvest sprouting.

Contaminação por mercúrio no Brasil: fontes industriais vs garimpo de ouro

This paper reviews the history of Hg contamination in Brazil by characterizing and quantifying two major sources of Hg emissions to the environment: industrial sources and gold mining. Industry was responsible for nearly 100% of total Hg emissions from the late 1940's to the early 1970's, when efficient control policies were enforced, leading to a decrease in emissions. Gold mining, on the other hand was nearly insignificant as a Hg source up to the late 1970's, but presently is responsible for over 80% of total emissions. Presently, over 115 tons of Hg are released into the atmosphere in Brazil annually. Nearly 78 tons come from gold mining operations, 12 tons come from chlor-alkali industry and 25 tons come from all other industrial uses. Inputs to soils and waters however, are still unknown, due to lack of detailed data base. However, emissions from diffuse sources rather than well studied classical industrial sources are probably responsible for the major inputs of mercury to these compartments.