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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 34 (1996), S. 259-264 
    ISSN: 1572-9680
    Keywords: Acer pseudoplatanus ; damage ; Fraxinus excelsior ; herbivory ; plastic tree-shelters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Direct herbivore damage to trees in temperate silvopastoral agroforestry systems is a major management consideration. Individual plastic tree-shelters may sometimes cause poor tree development and they have limited life span. Therefore, some alternative tree-shelter products were tested on four year old Acer pseudoplatanus and Fraxinus excelsior. Damage to the main stem was assessed by determining the area of bark removed by sheep browsing. Wobra®, a paint-on abrasive substance applied to the main stem, was effective in reducing sheep damage. However, some damage did occur due to breach of the protective barrier as a result of stem diameter increases and its removal through rubbing by animals. Anipel®, a systemic bittering agent supplied through the root system, was not effective in preventing significant damage compared to no-treatment controls, possibly because of poor uptake of the active ingredient into the tree. Within treatments, there were significant differences in damage incurred. Most notably Fraxinus suffered more damage than Acer, an effect which may be related to differences in tree size and/or relative palatability.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-6857
    Keywords: in situ ; hybridization ; centromeres ; retrotransposons ; genome organization ; evolution ; sequence evolution ; Arabidopsis ; barley
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Retrotransposons make up a major fraction – sometimes more than 40% – of all plant genomes investigated so far. We have isolated the reverse transcriptase domains of the Ty1-copia group elements from several species, ranging in genome size from some 100 Mbp to 23 000 Mbp, and determined the distribution patterns of these retrotransposons on metaphase chromosomes and within interphase nuclei by DNA:DNA in situ hybridization. With some exceptions, the reverse transcriptase domains were distributed over the length of the chromosomes. Exclusion from rDNA sites and some centromeres (e.g., slash pine, 23 000 Mbp, or barley, 5500 Mbp) is frequent, whereas many species exclude retrotransposons from other sites of heterochromatin (e.g., intercalary and centromeric sites in broad bean). In contrast, in the plant Arabidopsis thaliana, widely used for plant molecular genetic studies because of its small genome (c. 100 Mbp), the Ty1-copia group reverse transcriptase gene domains are concentrated in the centromeric regions, collocalizing with the 180 bp satellite sequence pAL1. Unlike the pAL1 sequence, however, the Ty1-copia signal is also detectable as weaker, diffuse hybridization along the lengths of the chromosomes. Possible mechanisms for evolution of the contrasting distributions are discussed. Understanding the physical distribution of retrotransposons and comparisons of the distribution between species is critical to understanding their evolution and the significance for generation of the new patterns of variability and in speciation.
    Type of Medium: Electronic Resource
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