Induction of triploidy in spotted sand bass (Paralabrax maculatofasciatus Steindachner, 1868) by cold shock

Conditions for the induction of triploidy with cold shock of fertilized eggs of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) were investigated. Different temperatures (12, 8 and 4 °C), timing of cold shock application (5, 10 and 15 min after fertilization) and duration of the shock (5, 10, 15 and 20 min) were tested. Triploidy was determined using flow cytometry at 12 h after larvae hatched. Triploids were produced only when the cold shock treatment was applied 5 min after fertilization. No significant difference was observed in the percentage of triploidy between temperature and the shock duration. At 8 and 4 °C, 100% triploidy was obtained at different durations of cold shock. Survival was significantly lower at 12 or 4 °C than at 8 °C. No significant difference was observed for shock duration at the temperature of 8 or 12 °C; however, at 4 °C, survival was significantly lower at longer durations. We recommend induction of triploidy by applying cold shock at 8 °C for a duration of 15–20 min starting at 5 min after fertilization, in the spotted sand bass.     

Hydrogen peroxide scavenging mechanisms are components of Medicago truncatula partial resistance to Aphanomyces euteiches

The biochemical processes underlying the expression of resistance in the roots of Medicago truncatula against Aphanomyces euteiches infection was investigated, with emphasis on oxidative stress. The levels of H₂O₂, superoxide dismutase, peroxidase, ascorbate peroxidase, catalase, soluble phenolics and lignin were measured in the roots of two lines, A17 partially resistant and F83005.5 susceptible to A. euteiches at three infection stages; penetration of the epidermis (1 dpi), colonization of the cortex (3 dpi) and invasion of the root stele (6 dpi). A rapid and large decrease of the H₂O₂ levels in A17 roots occurred. However, in F83005.5 roots, the decrease in H₂O₂ levels was delayed until 3 dpi. In A17 roots, the activities of ascorbate peroxidase, peroxidase and catalase were induced as early as 1 dpi, whereas a general decrease in the activity of the four antioxidant enzymes was observed in F83005.5 roots. The levels of soluble phenolics and lignin were increased in A17 roots at 3 and 6 dpi, respectively. The H₂O₂ levels were negatively correlated to ascorbate peroxidase, catalase and lignin production at 1, 3 and 6 dpi, respectively in A17 roots. Physiological concentrations of H₂O₂ found in M. truncatula infected roots had no detrimental effect on the in vitro growth of this oomycete. Our data suggest that H₂O₂ does not have a direct antimicrobial effect on M. truncatula resistance to A. euteiches, but is involved in cell wall strengthening around the root stele, preventing pathogen invasion of the vascular tissues.     

An Ulva armoricana extract protects plants against three powdery mildew pathogens

The protective activity of a crude extract prepared from the green macroalga, Ulva armoricana, previously shown to induce plant defence responses, was evaluated on three plant species, common bean, grapevine and cucumber, cultivated in the greenhouse and inoculated with three powdery mildew pathogens Erysiphe polygoni, E. necator and Sphareotheca fuliginea respectively. Chemical analyses showed that the extract was enriched in ulvans, which are green algae polysaccharides essentially composed of uronic acid and sulphated rhamnose. Weekly applications were performed by spraying of the green algal extract at various dilutions on bean, grapevine and cucumber leaves. A significant effect (50% protection) was observed using a dilution corresponding to about 3 g l⁻¹ dry matter and up to 90% reduction of symptom severity was obtained for the highest concentration (1/9 dilution, 6 g l⁻¹ dry matter) for the three plant species. To study the natural variability of the protective activity, five extracts prepared from algae batches harvested at different year periods were evaluated. Although polysaccharide composition varied among batches, all extracts elicit a reporter gene regulated by a defence-gene promoter in a transgenic tobacco line, and protect cucumber plants against powdery mildew infection. Together, these data demonstrate that U. armoricana is a reproducible source of active compounds which can be used to efficiently protect crop plants against powdery mildew diseases.     

Salmonella Cerro isolated over the past twenty years from various sources in the US represent a single predominant pulsed-field gel electrophoresis type

Salmonella Cerro prevalence in US dairy cattle has increased significantly during the past decade. Comparison of 237 Salmonella isolates collected from various human and animal sources between 1986 and 2009 using pulsed-field gel electrophoresis, antimicrobial resistance typing, and spvA screening, showed very limited genetic diversity, indicating clonality of this serotype. Improved subtyping methods are clearly needed to analyze the potential emergence of this serotype. Our results thus emphasize the critical importance of population-based pathogen surveillance for the detection and characterization of potentially emerging pathogens, and caution to critically evaluate the adequacy of diagnostic tests for a given study population and diagnostic application.     

Identification and preliminary characterization of a 75-kDa hemin- and hemoglobin-binding outer membrane protein of Actinobacillus pleuropneumoniae serotype 1

The reference strains representing serotypes 1 to 12 of Actinobacillus pleuropneumoniae biotype 1 were examined for their ability to utilize porcine hemoglobin (Hb) or porcine hemin (Hm) as iron sources for growth. In a growth promotion assay, all of the reference strains were able to use porcine Hb, and all strains except 2 were able to use porcine Hm. Using a preliminary characterization procedure with Hm- or Hb-agarose, Hm- and Hb-binding outer membrane proteins (OMPs) of approximately 75 kDa were isolated from A. pleuropneumoniae serotype 1 strain 4074 grown under iron-restricted conditions. Matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) analysis revealed a number of common tryptic peptides between the Hb-agarose- and Hm-agarose-purified 75 kDa OMPs, strongly suggesting that these peptides originate from the same protein. A database search of these peptide sequences revealed identities with proteins from various Gram-negative bacteria, including iron-regulated OMPs, transporter proteins, as well as TonB-dependent receptors. Taken together, our data suggest that A. pleuropneumoniae synthesizes potential Hm- and Hb-binding proteins that could be implicated in the iron uptake from porcine Hb and Hm.     

Does the effect of forest roads extend a few meters or more into the adjacent forest? A study on understory plant diversity in managed oak stands

Roads are recognised as having different ecological roles such as barrier, corridor or habitat, but the spatial extent of road effects on plant communities in forests remains unclear. We studied the effect of forest road distance on plant understory diversity at 20 sites in young and adult oak stands in a French lowland forest with a long history of management and road construction. All vascular and bryophyte species were collected at five distances ranging from the road verge to 100 m into the adjacent forest stand. We analysed species composition, individual species response, a priori life-history traits response – life form, habitat preference and dispersal mode – and environmental indicator values in relation to road distance and stand age. Plant composition strongly differed between road verge and forest interior habitats. The main road effect extended less than 5 m into the forest stand. A third habitat was detected at the forest-road edge resulting from the road effect on light and soil conditions, and from edge-specific topography. Non-forest species were almost absent from the forest interior. In contrast, many bryophytes and several vascular plants kept away from the road. We identified a posteriori six species groups that better explained the variability of plant response profiles than a priori life-history traits. Plant response to road distance was also dependent on stand age: some species colonised from the road into the forest interior in young stands following regeneration cutting, while other species displayed the reverse pattern in adult stands once canopy closed above the forest road. Even if the depth of forest road effect measured in lowland managed stands was narrow, building of a new forest road has non-negligible effects on plant population dynamics. Forest managers should take into account the impacts of roads on biodiversity, since the expected intensification of silviculture in response to global changes is set to accentuate the effect of forest roads. We recommend further study on the role of dispersal by vehicles (i.e. agestochory) in road effects.     

Approaches for controlling sea lice infestation in global salmon farming: What is applicable in Canadian aquaculture industry

ABSTRACT

This article describes the sea lice control methods that are currently applicable to salmon farming in Canada. Three commercial chemical products are approved for use against sea lice in Canada: Slice®, Interox® Paramove® 50, and Calicide®. Physical control methods include photoperiod and cage-depth manipulations, desiccation of farm equipment, and the use of electric fences. Biological control measures include the polyculture of salmon with wrasse or mussel. Nutraceuticals and immunostimulants shown to reduce sea lice infestations in salmon include unmethylated DNA, yeast fermentation extract-Brewer’s yeast compound, AllBrew and NuPro, MacroGard®, and Optimûn®. Salmon farmers are recommended to use site-specific integrated approaches, by properly adapting a combination of chemical, physical, biological, and nutritional measures to the environmental and financial characteristics of their farm. In the future, development of vaccines against sea lice and of salmon lines resistant to sea lice will play a pivotal role in fighting against this parasite.     

Effects of culture conditions on feeding response of larval Pacific red snapper ( Lutjanus peru, Nichols & Murphy) at first feeding

Feeding incidence or number of larvae with preys (FIC) and intensity or number of prey per larvae (FIT) at first feeding of Pacific red snapper ( Lutjanus peru) larvae was investigated under different conditions: prey type (rotifer and copepod nauplius) and density, nauplii size, light intensity, water temperature, salinity and microalgae concentration. Rotifers were not consumed at any prey density and FIC increased significantly when a high nauplii density (10 > 1, 0.1 mL^?1) and light intensity (2000 > 1000, 500, 0 lx) were supplied. In a multifactorial experiment where light intensity (2000, 2500, 3000 lx), tank colour (grey and black) and prey type (nauplii and a mixed diet: rotifers and nauplii) were tested, a significant difference was found only for light intensity and prey type with a significant interaction between these factors. FIC was significantly higher with nauplii stage I–III than IV–VI and also at 25 °C than at 28 °C. Green water (0, 0.3 × 10⁶ or 1 × 10⁶ cells mL^?1) and salinity (25, 30, 35 gL^?1) did not affect FIC. FIT was not affected by any variables tested except in the density experiment where it was significantly higher at 10 nauplii mL^?1.