Endonucléases de restriction: isolement et identification d'une souche d'adénovirus canin de type 1

For the first time in Quebec, a type 1 canine adenovirus was isolated in cell culture and typed by restriction endonuclease analysis. This virus originated from the internal organs of a young dog killed by a severe respiratory disease without showing any sign of hepatitis.     

Molecular Evidence of Distinct Introductions of the European Race of Gremmeniella abietina into North America

ABSTRACT The presence of the European (EU) race of Gremmeniella abietina var. abietina, the causal agent of Scleroderris canker of conifers, was first reported in North America in 1975 in the northeastern United States and subsequently in southern Quebec and Newfoundland during the late 1970s, where it quickly became established. We analyzed DNA profiles in samples from a historic collection of G. abietina var. abietina that included some of the first isolates of the EU race reported in the United States to test hypotheses concerning the G. abietina var. abietina epidemic in North America. Genetic diversity was partitioned by an analysis of molecular variance with haplotype frequencies and distances. Genetic differentiation was high between populations in continental North America and Newfoundland (between region differentiation, Phi(ct) = 0.665, P < 0.001). This result was not consistent with the hypothesis of a single introduction of the pathogen into the northeastern United States followed by secondary spread into northeastern Canada. In contrast, small levels of genetic differentiation were observed among continental North American populations (Phi(ct) = 0.047, P = 0.079), suggesting gene flow among these populations. A single haplotype of G. abietina var. abietina dominated the continental populations (80% of the isolates) but was absent from Newfoundland and Europe. Five haplotypes were found in the New-foundland population, all of which were either absent or very rare on the continent. Populations from continental North America clustered together and were distinct from a second cluster composed of European and Newfoundland populations. A phylogenetic analysis of the haplotypes indicated that some of the rare haplotypes may have derived from somatic mutations, whereas others probably occurred as the result of new introductions. The results are consistent with a scenario of distinct primary introductions of this pathogen into Newfoundland and continental eastern North America followed by secondary asexual propagation.     

Random amplified microsatellites (RAMS) — a novel method for characterizing genetic variation within fungi

A novel method, Random Amplified Microsatellites (RAMS, due to the nature of amplified markers as two randomly amplified microsatellites with the intervening sequence), was applied to generate DNA markers in a variety of fungi (Armillaria cepistipes, Gremmeniella abietina, Heterobasidion annosum, Pbytophthora cactorum, Phlebiopsis gigantea, and Stereum sanguinolentum). It is based on the polymerase chain reaction (PCR), and uses primers containing microsatellite sequences and degenerate anchors at the 5' end. The method is highly reproducible, applicable to all tested fungal species including members of the Phycomycetes, Ascomycetes and Basidiomycetes, and allows detection of interspecific and intraspecific DNA-polymorphisms.     

Genetic Diversity and the Presence of Two Distinct Groups in Ophiostoma clavigerum Associated with Dendroctonus ponderosae in British Columbia and the Northern Rocky Mountains

ABSTRACT The sapstaining fungal pathogen Ophiostoma clavigerum is associated with the mountain pine beetle (Dendroctonus ponderosae), which is currently the most destructive forest pest in North America. The genetic diversity of O. clavigerum populations collected from five sites in Canada and two sites in the United States was estimated with amplified fragment length polymorphism (AFLP) analysis. Genomic DNA from 170 O. clavigerum isolates was digested with EcoRI and PstI and amplified with six primer sets. A total of 469 AFLP markers consisting of 243 monomorphic and 226 polymorphic loci were scored. The overall genetic diversity of the O. clavigerum population was low (Hs = 0.0531) and the differentiation of the seven O. clavigerum populations was moderate (Phi = 0.143). Genetic distances among the populations were not significantly correlated with geographic distance (r = 0.3235, P = 0.074). Two genetically distinct groups in the O. clavigerum populations were shown by unique AFLP profiles and the unweighted pair group method with arithmetic averages. Further work to characterize biological differences between the two groups will be needed to confirm whether cryptic species are present in the O. clavigerum population.     

Genetic Diversity in Poplar Leaf Rust (Melampsora medusae f. sp. deltoidae) in the Zones of Host Sympatry and Allopatry

ABSTRACT Poplar leaf rust caused by Melampsora medusae f. sp. deltoidae is a widespread disease in North America, where epidemics occur within zones of sympatry and allopatry of telial hosts (Populus spp.) and aecial hosts (Larix spp.). To test the hypothesis that epidemics originate in the zone of sympatry where the rust can complete its life cycle, populations in sympatry and allopatry were analyzed with single-strand conformational polymorphism for codominant detection of alleles directly from uredinia. More alleles were detected in rust populations in the zone of host sympatry than in allopatry. Almost all alleles found in the zone of allopatry were a subset of the allelic diversity present in the zone of host sympatry. Distance analyses clustered populations according to geographic origin, but not sampling year or type of stand (plantation or natural stands). Large differences in allelic and genotypic frequency were observed between years in allopatry but not in sympatry, suggesting new colonizations in allopatric populations. Our results point to a dynamic and complex pattern of inoculum dissemination in polar leaf rust. The hypothesis most consistent with our results is that populations in sympatry represent a source of inoculum for epidemics, with some annual recolonization in allopatry, possibly via intermediate population jumps.     

Monensin controlled-release intraruminal capsule for control of bloat in pastured dairy cows

Monensin, a polyether ionophore antibiotic, is potentially an important agent for bloat relief in dairy cows grazing temperate legume-based pasture. A series of studies was undertaken to determine the effect of monensin, when delivered continuously in the rumen of lactating dairy cows by means of controlled-release capsules (monensin CRC). Such devices release approximately 300 mg/head/day for 100 d. A short-term pilot study made at Ruakura, New Zealand, tested monensin CRC in cows selected for high susceptibility to bloat and grazing lucerne (Medicago sativa) or red clover (Trifolium pratense). Treatment significantly reduced the incidence of bloat, while milk yield and protein yield were increased. There was no effect on fat yield. Following the pilot study, 6 large-scale field experiments involving a total of 368 lactating dairy cows, were made in Australia and New Zealand to confirm the effectiveness of monensin CRC for bloat control and to measure the effect of such treatment on milk production and composition. A severe bloat problem occurred in 2 experiments, mild bloat occurred in 2 others, while no visual signs of bloat were observed in the remaining 2 experiments. Bloat was significantly (P less than 0.05) reduced by monensin CRC treatment when data was pooled over the 4 experiments in which bloat occurred. Daily milk yield was increased in all experiments from a mean of 17.7 in untreated groups to 18.8 kg/head/day (P less than 0.05) in monensin CRC-treated cows. Protein percentage was not affected by treatment, while there was a decrease from 4.29 to 4.10% fat, although total fat yield was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rotavirus excretion by village pigs in Papua New Guinea

Cohort studies were conducted on 29 pigs from 3 villages in the Highlands of Papua New Guinea. Animals ranged in age from 9 d to 5 m old. Three hundred and twenty nine faecal samples were collected from individual pigs followed over 3 to 6 w periods, and were examined for group A rotavirus antigen by ELISA, and rotaviral genomic RNA by polyacrylamide gel electrophoresis (PAGE). Electron microscopy was also conducted on selected samples. Group A rotavirus was detected in the faeces of 16 pigs with infected individuals coming from all villages. Non-group A rotavirus resembling group C was found in faeces from pigs from 2 villages. All of the group A rotaviruses examined had the same electrophoretype and this was distinct from that of the common type infecting humans in the area at the time of the study. None of the group A positive samples reacted with monoclonal antisera specific for human group A rotaviruses of serotypes 1, 2, 3, 4, or 8. The non-group A rotaviruses also all had identical electrophoretypes. In contrast to previous findings in intensive piggeries, rotavirus infection did not occur in all young pigs and was not limited to young animals under 2 m of age. Infected pigs varied in age from 12 days to 20 weeks of age. This pattern of infection was attributed to the non-intensive husbandry situations in the villages, with less opportunity for transmission to occur than in intensive piggeries.     

The Breakdown of Olivine to Perovskite and Magnesiowustite

San Carlos olivine crystals under laboratory conditions of 26 gigapascals and 973 to 1473 kelvin (conditions typical of subducted slabs at a depth of 720 kilometers) for periods of a few minutes to 19 hours transformed to the phase assemblage of perovskite and magnesiowustite in two stages: (i) the oxygen sublattice transformed into a cubic close-packed lattice, forming a metastable spinelloid, and (ii) at higher temperatures or longer run durations, this spinelloid broke down to perovskite and magnesiowustite by redistributing silicon and magnesium while maintaining the general oxygen framework. The breakdown was characterized by a blocking temperature of 1000 kelvin, below which olivine remained metastable, and by rapid kinetics once the reaction was activated.