Effect of brushwood transposition on the leaf litter arthropod fauna in a cerrado area

The results of ecological restoration techniques can be monitored through biological indicators of soil quality such as the leaf litter arthropod fauna. This study aimed to determine the immediate effect of brushwood transposition transferred from an area of native vegetation to a disturbed area, on the leaf litter arthropod fauna in a degraded cerrado area. The arthropod fauna of four areas was compared: a degraded area with signal grass, two experimental brushwood transposition areas, with and without castor oil plants, and an area of native cerrado. In total, 7,660 individuals belonging to 23 taxa were sampled. Acari and Collembola were the most abundant taxa in all studied areas, followed by Coleoptera, Diptera, Hemiptera, Hymenoptera, and Symphyla. The brushwood transposition area without castor oil plants had the lowest abundance and dominance and the highest diversity of all areas, providing evidence of changes in the soil community. Conversely, the results showed that the presence of castor oil plants hampered early succession, negatively affecting ecological restoration in this area.

Differential Behavior of Young Eucalyptus Clones in Response to Nitrogen Supply

Eucalyptus requires large amounts of nitrogen (N); however, it responds in diverse manners to the application of this nutrient. The aim of this study was to evaluate the differential performance in growth, mineral nutrition, and gas exchanges of N-fertilized Eucalyptus clones. The treatments consisted of two Eucalyptus clones (VM-01 and I-144) and six N application rates (0, 0.74, 2.93, 4.39, 5.85, and 8 mmol L-1 NH4NO3) arranged in a randomized complete block design with five replications. VM-01 had greater plant height and greater height/collar diameter ratio, as well as higher leaf concentrations of all macronutrients and of Cu, Fe, Mo, and Zn. In terms of total and root dry matter production, root/shoot ratio, and collar diameter, as well as stomatal conductance and transpiration, I-144 performed better. The performance of the clones was clearly differentiated, and the growth of I-144, despite lower leaf N concentration, was in general better than VM-01.

LEAF TOTAL NITROGEN CONCENTRATION AS AN INDICATOR OF NITROGEN STATUS FOR PLANTLETS AND YOUNG PLANTS OF EUCALYPTUS CLONES

The use of leaf total nitrogen concentration as an indicator for nutritional diagnosis has some limitations. The objective of this study was to determine the reliability of total N concentration as an indicator of N status for eucalyptus clones, and to compare it with alternative indicators. A greenhouse experiment was carried out in a randomized complete block design in a 2 × 6 factorial arrangement with plantlets of two eucalyptus clones (140 days old) and six levels of N in the nutrient solution. In addition, a field experiment was carried out in a completely randomized design in a 2 × 2 × 2 × 3 factorial arrangement, consisting of two seasons, two regions, two young clones (approximately two years old), and three positions of crown leaf sampling. The field areas (regions) had contrasting soil physical and chemical properties, and their soil contents for total N, NH+4-N, and NO−3-N were determined in five soil layers, up to a depth of 1.0 m. We evaluated the following indicators of plant N status in roots and leaves: contents of total N, NH+4-N, NO−3-N, and chlorophyll; N/P ratio; and chlorophyll meter readings on the leaves. Ammonium (root) and NO−3-N (root and leaf) efficiently predicted N requirements for eucalyptus plantlets in the greenhouse. Similarly, leaf N/P, chlorophyll values, and chlorophyll meter readings provided good results in the greenhouse. However, leaf N/P did not reflect the soil N status, and the use of the chlorophyll meter could not be generalized for different genotypes. Leaf total N concentration is not an ideal indicator, but it and the chlorophyll levels best represent the soil N status for young eucalyptus clones under field conditions.

Physiological responses of two tropical weeds to shade: II. Leaf gas exchange and nitrogen content

Ipomoea asarifolia (Desr.) Roem. & Schultz (Convolvulaceae) and Stachytarpheta cayennensis (Rich) Vahl. (Verbenaceae), two weeds found in pastures and crop areas in the Brazilian Amazonia, Brazil, were grown in controlled environment cabinets under high (800-1000 µmol m-² s-¹) and low (200-350 µmol m-² s-¹) light regimes during a 40-day period. The objective was to determine the effect of shade on photosynthetic features and leaf nitrogen content of I. asarifolia and S. cayennensis. High-irradiance grown I. asarifolia leaves had significantly higher dark respiration and light saturated rates of photosynthesis than low-irradiance leaves. No significant differences for these traits, between treatments, were observed in S. cayennensis. Low-irradiance leaves of both species displayed higher CO2 assimilation rates under low irradiance. High-irradiance grown leaves of both species had less nitrogen per unit of weight. Low-irradiance S. cayennensis had more nitrogen per unit of leaf area than high-irradiance plants; however, I. asarifolia showed no consistent pattern for this variable through time. For S. cayennensis, leaf nitrogen content and CO2 assimilation were inversely correlated to the amount of biomass allocated to developing reproductive structures. These results are discussed in relation to their ecological and weed management implications.

Aspects of leaf anatomy of kudzu (Pueraria lobata, Leguminosae-Faboideae) related to water and energy balance

Kudzu is a cover crop that has escaped cultivation in some subtropical and warm temperate regions. Kudzu has previously demonstrated broad intraspecific physiological plasticity while colonizing new environments. The objective of this paper was to investigate characteristics of kudzu leaflet anatomy that might contribute to its successful growth in climatically distinct environments, and to escape cultivation as well. Fresh and fixed leaflet strips of field-grown plants were analyzed. The lower epidermis of kudzu showed a higher frequency of stomata (147 ± 19 stomata mm-2) than the upper epidermis (26 ± 17 stomata mm-2). The average number of trichomes per square milimeter was 8 for both the upper and the lower epidermis. The average trichome length was 410 ± 200 mum for the upper epidermis and 460 ± 190 mum for the lower epidermis. Cuticle thickness was not considerably different between lower and upper epidermis. The leaflet blade consisted basically of two layers (upper and lower) of unicellular epidermis, two layers of palisade parenchyma and one layer of spongy parenchyma. One layer of paraveinal mesophyll was found between palisade and spongy parenchyma. In conclusion, leaflets of kudzu present anatomical characteristics that might contribute to the broad physiological plasticity shown by kudzu.

ANATOMICAL STUDIES OF IN VITRO ORGANOGENESIS INDUCED IN LEAF-DERIVED EXPLANTS OF PASSIONFRUIT

With the aim of studying the organogenesis in vitro in Passiflora edulis Sims f. flavicarpa Deg., the passionfruit, leaf-derived explants were cultured on media containing NAA or BAP and incubated either in continuous darkness or in light. The histological events leading to de novo organ formation were evaluated. Darkness induces rhizogenesis in the presence of NAA, whereas direct shoot regeneration is stimulated by light and BAP. This latter condition is recommended for passionfruit micropropagation as several adventitious shoot buds were formed from meristemoids of parenchymal origin.

Physiological responses of maize and cowpea to intercropping

The effect of intercropping on plant water status, gas exchange and productivity of maize (Zea mays L.) cv. Centralmex, and cowpea (Vigna unguiculata L. (Walp)) cv. Pitiuba were evaluated under semi-arid conditions at the Embrapa-Centro de Pesquisa Agropecuária do Trópico Semi-Árido (CPATSA) at Petrolina, PE, Brazil. The treatments were: maize and cowpea as sole crops, at a population of 40,000 plants ha-1, and intercropped at a population of 20,000 plants ha-1. The results obtained in this paper appear to be related to the degree of competition experienced by the components, mainly for water and light. Maize intercropped had higher values of leaf water potential, stomatal conductance, transpiration and photosynthesis than as sole crop. Intercropped cowpea had higher values of leaf water potential but lower stomatal conductance, transpiration and photosynthesis than sole cowpea. Maize productivity increased 18% in relation to sole crop whereas a 5% decrease was observed with cowpea. Despite these facts the Land Equivalent Ratio obtained was 1.13 indicating intercropping advantage over the sole system. The higher partial Land Equivalent Ratio observed for maize suggests that this specie was the main component influencing the final productivity of the intercropping system studied.

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.

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.

Effects of leaf compounds, climate and natural enemies on the incidence of thrips in cassava

The objective of this study was to determine the effects of rainfall, temperature, sunlight and relative humidity, as well as predators and parasitoids, leaf chemical composition and levels of leaf nitrogen and potassium on the intensity of Scirtothrips manihoti (Thysanoptera: Thripidae) attack on cassava Manihot esculenta Crantz var. Cacau. The leaf compounds (E)-farnesene/trans-farnesol and D-friedoolean-14-en-3-one correlated significantly with the population of S. manihoti. Insect population decreased in the dry and cold season probably due to leaf senescence. Significative correlation was observed between Syrphidae with S. manihoti populations.

Diallel analysis for frogeye leaf spot resistance in soybean

Seven soybean cultivars (Bossier, Cristalina, Davis, Kent, Lincoln, Paraná and Uberaba), with different levels of resistance to Cercospora sojina, were crossed in a diallel design to determine the general (GCA) and specific (SCA) combining abilities relative to the inheritance of the resistance. Race 04 of the fungus was inoculated in the parents and in the 21 F1 hybrids in a greenhouse in a completely randomized design, with 12 replications. The reactions to the disease were evaluated 20 days after the inoculation, always on the most infected leaflet. Both GCA and SCA were significant for all the evaluated characters, being inferred that, for the expression of the characters, the additive, dominant and, possibly, epistatic genic actions were important. The largest values of estimated SCA effect (ij) were observed in the hybrid combinations where at least one parent presented high GCA. Cristalina, Davis and Uberaba cultivars showed the largest estimates for GCA effect (i), and from the analysis of ii, the contribution of these parents to heterosis of their hybrids will be towards the reduction of the disease symptoms. Therefore, these cultivars are indicated as parents in breeding programs that seek the development of soybean cultivars with resistance to frogeye leaf spot.

Environmental effects on photosynthetic capacity of bean genotypes

Photosynthetic responses to daily environmental changes were studied in bean (Phaseolus vulgaris L.) genotypes 'Carioca', 'Ouro Negro', and Guarumbé. Light response curves of CO2 assimilation and stomatal conductance (g s) were also evaluated under controlled (optimum) environmental condition. Under this condition, CO2 assimilation of 'Carioca' was not saturated at 2,000 µmol m-2 s-1, whereas Guarumbé and 'Ouro Negro' exhibited different levels of light saturation. All genotypes showed dynamic photoinhibition and reversible increase in the minimum chlorophyll fluorescence yield under natural condition, as well as lower photosynthetic capacity when compared with optimum environmental condition. Since differences in g s were not observed between natural and controlled conditions for Guarumbé and 'Ouro Negro', the lower photosynthetic capacity of these genotypes under natural condition seems to be caused by high temperature effects on biochemical reactions, as suggested by increased alternative electron sinks. The highest g s values of 'Carioca' were observed at controlled condition, providing evidences that reduction of photosynthetic capacity at natural condition was due to low g s in addition to the high temperature effects on the photosynthetic apparatus. 'Carioca' exhibited the highest photosynthetic rates under optimum environmental condition, and was more affected by daily changes of air temperature and leaf-to-air vapor pressure difference.

Ecophysiological response of Sorghum halepense populations to reduced rates of nicosulfuron

The control and regrowth after nicosulfuron reduced rate treatment of Johnsongrass (Sorghum halepense L. Pers.) populations, from seven Argentinean locations, were evaluated in pot experiments to assess if differential performance could limit the design and implementation of integrated weed management programs. Populations from humid regions registered a higher sensibility to reduced rates of nicosulfuron than populations from subhumid regions. This effect was visualised in the values of regression coefficient of the non-linear models (relating fresh weight to nicosulfuron rate), and in the time needed to obtain a 50% reduction of photosynthesis rate and stomatal conductance. The least leaf CO2 exchange of subhumid populations could result in a lower foliar absorption and translocation of nicosulfuron, thus producing less control and increasing their ability to sprout and produce new aerial biomass. The three populations from subhumid regions, with less sensibility to nicosulfuron rates, presented substantial difference in fresh weight, total rhizome length and number of rhizome nodes, when they were evaluated 20 week after treatment. In consequence, a substantial Johnsongrass re-infestation could occur, if rates below one-half of nicosulfuron labeled rate were used to control Johnsongrass in subhumid regions.

Somatic embryogenesis and in vitro plant regeneration from pejibaye adult plant leaf primordia

The aim of this work was to evaluate a protocol for plant regeneration by means of somatic embryos obtained from isolated adult pejibaye leaf primordia, and to describe histological origin of embryos and morphogenetic response. Explants were cultivated in modified MS medium. Mesophyll parenchymatous cells originated meristemoids (preembryonic complex formation) induced with 7.1 µM BAP in the first two subculture periods. After polarized structures with 12.9 µM NAA and 3.55 µM BAP were formed in the third subculture, somatic embryos developed and regenerated normal plants. The mesophyll parenchymatous cells display high capacity of direct response to the auxin and cytokinin.

Study of simple sequence repeat markers from coffee expressed sequences associated to leaf miner resistance

The objective of this work was to identify expressed simple sequence repeats (SSR) markers associated to leaf miner resistance in coffee progenies. Identification of SSR markers was accomplished by directed searches on the Brazilian Coffee Expressed Sequence Tags (EST) database. Sequence analysis of 32 selected SSR loci showed that 65% repeats are of tetra-, 21% of tri- and 14% of dinucleotides. Also, expressed SSR are localized frequently in the 5'-UTR of gene transcript. Moreover, most of the genes containing SSR are associated with defense mechanisms. Polymorphisms were analyzed in progenies segregating for resistance to the leaf miner and corresponding to advanced generations of a Coffea arabica x Coffea racemosa hybrid. Frequency of SSR alleles was 2.1 per locus. However, no polymorphism associated with leaf miner resistance was identified. These results suggest that marker-assisted selection in coffee breeding should be performed on the initial cross, in which genetic variability is still significant.