Early detection of bovine leukosis virus DNA in infected sheep using the polymerase chain reaction.

The early diagnosis of bovine leukosis virus (BLV) infection, the aetiological agent in enzootic bovine leukosis, is important for the implementation of control measures. BLV infection is currently assessed by the detection of circulating antibodies against the viral envelope protein, gp51. However, this approach has shortcomings in the time taken to detect anti-BLV antibodies (three to four weeks after infection), and in the failure to detect antibodies in some animals. Clearly a technique such as the polymerase chain reaction (PCR), which directly detects the presence of viral DNA, has advantages over methods designed to measure host antibodies. The use of PCR for the detection of proviral DNA in an affected DNA sample with as little as 10(-5) micrograms of host DNA using agarose gel electrophoresis followed by ethidium bromide staining is described here. It was possible to improve the sensitivity of this assay by using hybridisation analysis with a BLV gene probe. PCR used in combination with hybridisation analysis will provide a sensitive diagnostic assay to detect BLV when antibody tests give weakly positive or equivocal results.     

Stand-replacing patches within a ‘mixed severity’ fire regime: quantitative characterization using recent fires in a long-established natural fire area

The complexity inherent in variable, or mixed-severity fire regimes makes quantitative characterization of important fire regime attributes (e.g., proportion of landscape burned at different severities, size and distribution of stand-replacing patches) difficult. As a result, there is ambiguity associated with the term ‘mixed-severity’. We address this ambiguity through spatial analysis of two recent wildland fires in upper elevation mixed-conifer forests that occurred in an area with over 30 years of relatively freely-burning natural fires. We take advantage of robust estimates of fire severity and detailed spatial datasets to investigate patterns and controls on stand-replacing patches within these fires. Stand-replacing patches made up 15% of the total burned area between the two fires, which consisted of many small patches (<4 ha) and few large patches (>60 ha). Smaller stand-replacing patches were generally associated with shrub-dominated (Arctostaphylos spp. and Ceanothus spp.) and pine-dominated vegetation types, while larger stand-replacing patches tended to occur in more shade-tolerant, fir-dominated types. Additionally, in shrub-dominated types stand-replacing patches were often constrained to the underlying patch of vegetation, which for the shrub type were smaller across the two fire areas than vegetation patches for all other dominant vegetation types. For white and red fir forest types we found little evidence of vegetation patch constraint on the extent of stand-replacing patches. The patch dynamics we identified can be used to inform management strategies for landscapes in similar forest types.     

Discriminating power of microsatellites in cranberry organelles for taxonomic studies in <Emphasis Type="Italic">Vaccinium</Emphasis> and Ericaceae

Simple sequence repeats (SSRs) in chloroplast and mitochondrial DNA, which have not been previously developed in the Ericaceae or, more specifically, in the genus Vaccinium, can be powerful tools for determining evolutionary relationships among taxa. In this study, 30 chloroplast, 23 mitochondrial, and 1 mitochondrion-like SSRs were identified in cranberry (V. macrocarpon), and primer-pairs were developed and tested for each locus. Although no polymorphisms were detected for any of the 54 SSR loci in nine diverse cranberry genotypes, all primers were cross-transferable to some extent to a panel of 12 additional Vaccinium taxa and four non-Vaccinium Ericaceae species. A Neighbor-Joining tree of the estimated average squared distances resolved the species by genus and by section within Vaccinium. Similar topologies with increased branch support were observed in Bayesian inference trees constructed from the DNA sequences of six plastid and two mitochondrial SSR loci. Two multiplexing/poolplexing panels of M13 fluorescently labeled primers, which amplify 24 of the 54 markers, were developed and can serve as an efficient, cost-effective means for characterizing the basic molecular phylogeny of Vaccinium. Increased understanding of evolutionary relationships among Vaccinium species should facilitate interspecific hybridization and introgression efforts to improve economically important traits of commercial berry crops.