Increase in size and nitrogen concentration enhances seedling survival in Mediterranean plantations. Insights from an ecophysiological conceptual model of plant survival

Reduction in size and tissue nutrient concentration is widely considered to increase seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence indicates that increase in size and tissue nutrient concentration improves seedling survival in Mediterranean forest plantations. This suggests that the ecophysiological processes and functional attributes relevant for early seedling survival in Mediterranean climate must be reconsidered. We propose a ecophysiological conceptual model for seedling survival in Mediterranean-climate plantations to provide a physiological explanation of the frequent positive relationship between outplanting performance and seedling size and nutrient concentration. The model considers the physiological processes outlined in the plantation establishment model of Burdett (Can J For Res 20:415–427, 1990), but incorporates other physiological processes that drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics. The model considers that seedling survival in Mediterranean climates is linked to high growth capacity during the wet season. The model is for container plants and is based on three main principles, (1) Mediterranean climates are not dry the entire year but usually have two seasons of contrasting water availability; (2) summer drought is the main cause of seedling mortality; in this context, deep and large roots is a key trait for avoiding lethal water stress; (3) attainment of large root systems in the dry season is promoted when seedlings have high growth during the wet season. High growth is achieved when seedlings can divert large amount of resources to support new root and shoot growth. Functional traits that confer high photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage promote high growth. Increases in seedling size and nutrient concentration strongly affect these physiological processes. Traits that confer high drought resistance are of low value during the wet season because hinder growth capacity. We provide specific evidence to support the model and finally we discuss its implications and the factors that may alter the frequent increase in performance with increase in seedling size and tissue nutrient concentration.     

Biocontrol traits of plant growth suppressive arbuscular mycorrhizal fungi against root rot in tomato caused by <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis>

Arbuscular mycorrhizal (AM) fungi known to cause plant growth depressions in tomato were examined for their biocontrol effects against root rot caused by Pythium aphanidermatum. The main hypothesis was that plant growth suppressive AM fungi would elicit a defence response in the host plant reducing Pythium root rot development. To test this hypothesis a fully factorial experiment was performed with AM fungi (Glomus intraradices, G. mosseae, G. claroideum or nonmycorrhizal), Pythium (± P. aphanidermatum) and harvest (7 and 14 days after pathogen inoculation (dapi)) as the main factors. Two weeks after AM fungi inoculation, roots were challenged with P. aphanidermatum. Variables evaluated at each harvest were root colonization levels of the interacting fungi, plant growth responses, and expression of a plant pathogenesis related protein gene (PR-1). All of the tested AM fungi caused marked growth suppressions, but did not affect PR-1 gene expression or the phosphorous concentration in the host plant. Plants singly inoculated with P. aphanidermatum had an increased PR-1 expression and phosphorous concentration. Among the AM fungi included in the study only G. intraradices reduced the pathogen root infection level, measured both in terms of Pythium ELISA and by recovery on selective media and only at the first harvest. Likewise, P. aphanidermatum root infection reduced colonization levels of G. intraradices, but not that of the two other AM fungi. In conclusion, plant growth suppressive AM fungi may offer plant beneficial traits in terms of biocontrol of root cortical pathogens.     

Life history parameters and scale-cover surface area of Aonidiella aurantii are altered in a mating disruption environment: implications for biological control

BACKGROUND: In recent years, environmentally safe measures to control the California red scale (CRS), Aonidiella aurantii (Maskell), have been successfully implemented. These measures include mating disruption (MD) and biological control. The goal of this study was to examine the effect of high concentrations of the CRS sex pheromone on its life history parameters and scale‐cover surface area under controlled laboratory conditions. RESULTS: The developmental time of both males and females of CRS increased with exposure to airborne pheromone. MD had an effect on both the total number of progeny and on the crawler production period for females. Accordingly, demographic parameters such as net fecundity (R₀) and intrinsic rate of increase (r_m) were significantly lower in the pheromone‐treated populations. The largest scale‐cover surface areas were observed in the CRS reared in the pheromone environment. CONCLUSION: A clear influence of airborne pheromone on the biology of CRS has been demonstrated. In addition to the classical mating disruption benefits of this technique, additional benefits, such as increase in the duration of exposure to natural enemies and increase in size, which benefits some species of parasitoids, have been confirmed. Copyright © 2012 Society of Chemical Industry     

Virulence and Molecular Diversity within Colletotrichum lindemuthianum Isolates from Andean and Mesoamerican bean Varieties and Regions

Virulence on a standard set of 12 common bean differential varieties, DNA sequence of repetitive-elements (Rep-PCR) and random amplified microsatellites (RAMS) were used to assess the genetic variability of 200 Colletotrichum lindemuthianum isolates collected from Andean and Mesoamerican bean varieties and regions. High levels of pathotypic (90 pathotypes) and genetic diversity (0.97) were identified among 200 isolates, revealing that C. lindemuthianum is a highly diverse pathogen. Although a significant number of pathotypes were common to Andean and Mesoamerican regions, many more were only found in the Mesoamerican region. Cluster analysis of virulence and molecular data did not separate isolates into groups that were structured with common bean gene pools. No genetic differentiation (G _ST=0.03) was apparent between Andean and Mesoamerican isolates of C. lindemuthianum. The diversity exhibited by C. lindemuthianum does not appear to cluster according to common bean gene pools, and the high diversity found in the Mesoamerican region seems to indicate that C. lindemuthianum originated and was disseminated from this region. Due to the high genetic variation exhibited by C. lindemuthianum, stacking major resistance genes appears to be the best option for developing cultivars with durable anthracnose resistance.     

The use of cytochemistry,immunophenotyping, flow cytometry,and in vitro differentiation to determine the ontogeny of a canine monoblastic leukemia

We evaluated the utility of cytochemistry, immunophenotyping, flow cytometry, and in vitro culture with forced differentiation of leukemic cells as diagnostic aids to identify the malignant cell ontogeny in a dog with leukemia. A tentative diagnosis of monoblastic leukemia was established by microscopic examination of Romanowsky-stained blood smears and bone marrow aspirate smears. This diagnosis also was supported by the light scatter signature that identified the blast cells as large, non-granular monocytic cells using a CellDyn 3500 automated hematology analyzer; as well as by the detection of N-butyrate esterase and the lack of choloroacetate esterase or leukocyte peroxidase by cytochemical staining. Subsequently, leukemic cells were isolated from the dog's peripheral blood and placed into tissue culture or cryopreserved. The leukemic cells grew in suspension cultures and proliferated spontaneously for up to 4 days. By day 7, proliferation was negligible. Upon culture with conditioned supernatant using mitogen-stimulated human T cells as a source of cytokines, an increased proportion of cells entered S phase by day 2 of culture; however, proliferation declined markedly by day 4, at which time the cells had apparently differentiated to adherent, vacuolated macrophages. The cytokine-stimulated leukemic cells were positive for the monocyte/macrophage specific markers alpha-1-antitrypsin, alpha-1-antichymotrypsin, lysozyme, CD14, MHC class II, and calprotectin, an antigen found in differentiated macrophages and granulocytes. Despite the strong tendency of the leukemic cells towards monocytic differentiation, our results suggested that they retained some features of a myelomonocytic precursor. These data show that cytochemistry, immunophenotyping, flow cytometry, and in vitro differentiation of canine leukemia cells are useful tools for confirming the lineage of malignant hematopoietic cells.     

Modifications to physicochemical and nutritional properties of hard-To-cook beans (Phaseolus vulgaris L.) by extrusion cooking.

The objective of this work was to evaluate extrusion cooking as a means to improve the nutritional properties of Phaseolus vulgaris L. that had been stored either at 42 degrees C and 80% relative humidity for 6 weeks or for periods >1 year in cereal stores in tropical conditions. Storage under these conditions resulted in an increase in cooking time increased (7.7- and 12-fold, respectively) as a result of development of the hard-to-cook (HTC) defect. Single-screw extrusion of the milled beans was carried out at four barrel temperatures and two moisture contents. The extrudate bulk density and water solubility index decreased with increasing temperature, whereas the water absorption index increased due to the higher proportion of gelatinized starch in the extruded samples. Both fresh and HTC beans contained nutritionally significant amounts of lectins, trypsin, and alpha-amylase inhibitors, which were mostly inactivated by extrusion. Extrusion also caused a considerable redistribution of insoluble dietary fiber to soluble, although the total dietary fiber content was not affected. Changes in solubility involved pectic polysaccharides, arabinose and uronic acids being the main sugars involved. Stored beans subjected to extrusion cooking showed physical and chemical characteristics similar to those of extrudates from fresh beans.     

Selective Nixtamalization of Fractions of Maize Grain (Zea mays L.) and Their Use in the Preparation of Instant Tortilla Flours Analyzed Using Response Surface Methodology

Using a continuous decorticating machine, white dent corn was efficiently separated, after brief steeping in water, into two fractions: the first (12.5%) consisting mainly of pericarp, germ, and tip cap (PGT); the second (87.5%) consisting of endosperm. Nixtamalization of the maize fractions in the presence of 0.6% (w/w) lime caused an increase in the hot‐paste viscosity at 90°C, while nixtamalization of PGT at lime inputs <0.6% (w/w) resulted in decreased viscosity. Three domains were found for the viscosity of nixtamalized endosperm at 90°C: lower concentrations of lime (< 0.15%, w/w) resulted in lower viscosity values; increased lime (0.15% – <0.3%, w/w) increased the viscosity values; and a lime concentration of 0.3% (w/w) resulted in a lower viscosity value. The response variables (water absorption index, water solubility index, initial viscosity, and viscosity at 90°C for nixtamalized PGT, and compression force and compression area of tortillas) indicated that the mathematical models fit the experimental data and the variance of the models was highly significant. Tortillas of good functional characteristics similar to tortillas produced by the traditional process were obtained when 5% nixtamalized fractions of PGT were blended with 95% nixtamalized endosperm.     

Zebrafish (Danio rerio) as an animal model for bath infection by Flavobacterium psychrophilum

Flavobacterium psychrophilum is the causative agent of bacterial cold-water disease and rainbow trout syndrome in freshwater salmonid fish worldwide, generating injuries and high mortality rates. Despite several studies on this bacterium, the infection mechanism remains unknown due to limitations in the employed animal models. In this work, we propose using zebrafish (Danio rerio) as a model for studying bacterial pathogenicity. To substantiate this proposal, zebrafish infection by F. psychrophilum strain JIP 02/86 was characterized. Zebrafish larvae were infected using the bath method, and morphological changes and innate immune system activation were monitored using transgenic fish. Salmonid-like infection phenotypes were observed in 4.74% of treated larvae, as manifested by fin, muscle and caudal peduncle damage. Symptomatic and dead larvae accounted for 1.35% of all challenged larvae. Interestingly, infected larvae with no infection phenotypes showed stronger innate immune system activation than specimens with phenotypes. A failure of function assay for myeloid factor pu.1 resulted in more infected larvae (up to 43.5%), suggesting that low infection rates by F. psychrophilum would be due to the protective actions of the innate immune system against this bacterium in zebrafish larvae. Our results support the use of zebrafish as an infection model for studying F. psychrophilum. Furthermore, the percentage of infected fish can be modulated by disturbing, to varying extents, the differentiation of myeloid cells. Using this evidence as a starting point, different aspects of the infection mechanism of F. psychrophilum could be studied in vivo.     

Science,capacity building and conservation knowledge: The empowerment of the local community for marine conservation in Rapa Nui

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