Entérite nécrotique chez le pollet de gril III. Etude des facteurs favorisant la multiplication de Clostridium perfringens et la transmission expérimentale de la maladie

Necrotic enteritis was reproduced experimentally in two week old broiler chickens by intravenous injection and also by oral administration of a pure culture of Clostridium perfringens. In the first experiment, gross and microscopic intestinal lesions, typical of necrotic enteritis, were observed in all diseased birds and mortality was obtained only in the group of birds that were injected with 0.4 ml or more of the pure culture of the microorganism. In the second experiment, the highest mortality was noted in the group of birds that received orally, in addition to the Clostridium culture, a solution of sodium bicarbonate, to obtain an alkaline intestinal content and opium to decrease the intestinal peristaltism. The gross and microscopie intestinal lesions of the diseased and killed birds were more severe than those observed in the other groups and were similar to those encountered in field outbreaks of necrotic enteritis.     

Infection Respiratoire du Dindonneau Causee par un Microbe Apparente au Bordetella Bronchiseptica

A respiratory condition encountered in young turkeys is reported with the isolation of Bordetella bronchiseptica as the possible etiological agent. Rhinitis, bronchitis and bronchopneumonia were the main lesions caused by this bacteria. Transmission trials were successful in turkeys and chicken but not in mice. Guinea pigs were also infected for comparative pathological studies.     

Relationship between residual energy intake and the behaviour of growing pigs from three genetic lines

Residual metabolizable energy intake (RMEI) is the difference between metabolizable energy intake (MEI) and predicted production and maintenance requirements. In growing pigs from three genetic lines, namely Genex Meishan-derived dam line (GM), Synthetic Genex 3000 (SG) and purebred Large White (LW), RMEI was determined and related to behaviour by factorial Partial Least Squares analysis. Behaviour was measured by observations of daily behaviour in the pen, postures, feeding behaviour, aggressive behaviour after mixing and ease of handling at weighing. The RMEI obtained for the GM pigs was lower (P = 0.003) than that of the two other lines studied (LW and SG). This difference may result from inaccuracy in the estimation of requirements. A small proportion of these differences were explained by differences in behaviour. Indeed, standing posture, time spent in the feeder, toy manipulation, aggressive and locomotor behaviour explained part of the variation in RMEI, presumably because an increase in these physical activities induces higher energy expenditure. Vocalisations during manipulations at weighing were the only behaviour related to stress that influenced RMEI.     

Structural differences and functional similarities between two sugar maple (Acer saccharum) stands

The spatially inexplicit or functional multilayer models used to predict canopy transpiration or photosynthesis are based on the assumption that closed stands show less functional variability than structural variability, because foliage tends to arrange itself in space to optimize the capture of light. To validate this assumption, we compared the structural and functional properties, and the measured and modeled transpiration fluxes of two sugar maple (Acer saccharum Marsh.) stands of comparable leaf mass but differing in height and diameter distributions. One stand was characterized by a well-developed single-layer canopy, whereas the other stand had a multilayered canopy and a stem diameter distribution of the classical inverse-J shape. Stand differences in height and diameter distribution, and canopy gap fraction, were highly significant. There were minor but significant differences in leaf mass and leaf mass per unit leaf area (LMA) distributions. We found no differences in tree-level relationships between basal area and either transpiration flux or sapwood area. We compared measurements of stand transpiration with transpiration estimates obtained from a multilayer gas exchange model, in which only the nonspatial inputs, leaf area index and LMA frequency distribution described stand structure. For both stands, modeled values of daily transpiration closely followed measured values (r(2) = 0.94). These results support use of the nonspatially explicit approach to estimating canopy gas exchange, especially if the intent is to scale-up to larger portions of the landscape.     

Genetic transformation,electrophoretic karyotyping and isolation of insertional mutants in the tree pathogenic fungus Neonectria galligena

The ascomycete tree pathogen Neonectria galligena was transformed using several plasmid vectors containing the bacterial hygromycin phosphotransferase gene (hph) conferring resistance to hygromycin B. Protoplasts were produced by digesting germinating conidia in a Novozym 234 solution osmotically stabilized with NaCl. The protoplasts regenerated at ca. 70% on complete medium supplemented with either sucrose or NaCl. Up to 115 hygromycin B‐resistant transformants per microgram of transforming DNA per 10⁸ protoplasts were obtained. Southern analysis of genomic DNA from the transformants, separated by either standard agarose gel electrophoresis or by pulsed field gel electrophoresis, confirmed that hygromycin B resistance resulted from integration of the vector. Transformants expressing the green fluorescent protein were also obtained. A total of 209 transformants were then screened for aggressiveness and mycelial radial growth. Four mutants were identified including one mutant with reduced aggressiveness but normal growth in vitro, two mutants with reduced growth in vitro but normal aggressiveness, and one mutant in which both aggressiveness and in vitro growth were reduced.     

Importance of needle age and shoot structure on canopy net photosynthesis of balsam fir (Abies balsamea): a spatially inexplicit modeling analysis

We have developed a spatially inexplicit model of canopy photosynthesis for balsam fir (Abies balsamea (L.) Mill.) that accounts for key processes of light-shoot interaction including irradiance interception by the shoot, spatial aggregation of shoots into branches and crowns, the differential propagation of diffuse and direct light within the canopy, and an ideal representation of penumbra. Also accounted for in the model are the effects of the average radiative climate and shoot age on needle retention, light interception, and photosynthetic capacity. We used reduced versions of this model to quantify the effects of simplifying canopy representation on modeled canopy net photosynthesis. Simplifications explored were the omission of direct beam transformation into penumbral light and the use of different constant shoot properties throughout the canopy. The model was parameterized for a relatively dense balsam fir stand (leaf area index of 5.8) north of Québec City, Canada, and run using hourly meteorological data obtained at the site. The overall performance of the complete model was satisfactory, with maximum values of canopy net photosynthesis of 23 micromol (m(2) ground)(-1) s(-1) (83 mmol m(-2) h(-1)), and a near-saturation of the canopy at a photosynthetically active radiation photon flux density of about 750 micromol m(-2) s(-1) (2.7 mol m(-2) h(-1)). The omission of penumbral effects through the use of unattenuated direct (beam) radiation at all layers of the canopy, as used for broad-leaved species, reduced canopy net photosynthesis by 3.7%. Analysis of the results show that the small impact of penumbra on canopy net photosynthesis stems from the high proportion of diffuse radiation (73%) estimated from our meteorological data set; single-hour results under clear sky conditions approach theoretical bias values of about 30%. Use of mean shoot photosynthetic, light capture and light transmission properties throughout the canopy biased canopy net photosynthesis by less than 3%. However, simulations carried out based on properties of 1-year-old shoots throughout the canopy overestimated canopy net photosynthesis by 9%. Use of the shoot as our smallest functional unit was a potential source of bias because the differential absorption of direct and diffuse radiation within the shoot could not be factored into the model. Other sources of potential bias are discussed.     

Effect of Fall Application of Fungal Antagonists on Spring Ascospore Production of the Apple Scab Pathogen, Venturia inaequalis

ABSTRACT The influences of Microsphaeropsis sp., M. arundinis, Ophiostoma sp., Diplodia sp., and Trichoderma sp., all antagonists of Venturia inaequalis, on ascospore production were evaluated under natural conditions and compared with urea and Athelia bombacina, a known antagonist. In the autumn, the fungi were applied to leaf disks artificially inoculated with V. inaequalis and to scabbed apple (Malus domestica) leaves incubated under controlled and natural conditions. In addition, large-scale trials were conducted with Microsphaeropsis sp. applied either as a foliar postharvest spray or as a ground application at 90% leaf fall. All fungal isolates, except Ophiostoma sp., were recovered from the leaf material that overwintered in the orchard. All treatments, except those with Ophiostoma sp., resulted in a significant reduction in V. inaequalis ascospore production on the leaf disks incubated under controlled conditions or in the orchard. In 1997, leaves with apple scab lesions treated with urea or Microsphaeropsis sp. produced significantly fewer ascospores of V. inaequalis than did nontreated leaves, with a reduction of 73.0 and 76.3%, respectively. In 1998, leaves treated with Microsphaeropsis sp., urea, Trichoderma sp., A. bombacina, and M. arundinis reduced ascospore production by 84.3, 96.6, 75.2, 96.6, and 52.2%, respectively. Based on all tests combined, the most efficient isolate was Microsphaeropsis sp. Postharvest applications of Microsphaeropsis sp. reduced the total amount of airborne ascospores trapped by 70.7 and 79.8% as compared with the nontreated plots in 1997 and 1998, respectively. Microsphaeropsis sp. provided a significant and consistent reduction in ascospore production in all tests.     

Boreal lichen woodlands: A possible negative feedback to climate change in eastern North America

Because of successive forest fires, closed-canopy black spruce forests are susceptible to a shift towards open lichen-spruce woodlands in parts of the boreal forest of eastern North America. The shift from dark black spruce canopies to pale lichen ground cover offers a dramatic contrast in reflectance that may compensate for the CO₂ emissions from forest fires in terms of radiative forcing. We have therefore looked at the climate change feedback that would result from the generation of lichen woodlands through changes in albedo and in stored carbon. Using albedo estimates based on MODIS imagery and incoming solar radiation for the period between 2000 and 2008 along with forest biomass estimates for eastern Canada, we have estimated that net radiative forcing for the conversion from closed-canopy coniferous forests to open lichen woodlands would be about −0.12 nW m⁻² ha⁻¹, and would therefore generate a cooling effect in the atmosphere. Based on current estimates of area in open lichen woodlands within the closed-canopy black spruce-moss forests of eastern Canada, we estimate that a current net forcing of −0.094 mW m⁻² has already arisen from such conversions. As projections of future climate have been linked to increased probability of forest fires, the generation of open lichen woodlands provides a possible negative feedback to climate change. Results also suggest that carbon sequestration through the afforestation of boreal lichen woodlands may not provide a climate change mitigation benefit.