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THE STATUS OF TRADITIONAL SCOTTISH ANIMAL BREEDS AND PLANT VARIETIES AND THE IMPLICATIONS FOR BIODIVERSITY
CHAPTER THIRTEEN: IDENTIFICATION OF THE SIZE AND COMPLEXITY OF THE GENETIC RESOURCE WITHIN CROP VARIETIES AND IMPACTS ON GENETIC DIVERSITY OF REDUCED USE
13.1 Estimates of genetic diversity have been made in European spring barleys by the use of genetic markers such as AFLPs (Ellis et al, 1997) and SSRs (Russell et al, 2000). Scots Bere and other traditional cultivars have not been explored in a detailed examination of inbred lines from crosses, as in the case of the Derkado x B83-12/21/5 doubled haploid population (Thomas et al, 1998), but genome scanning has been carried out to assess allelic variation at a discrete number of genetic loci. The results of genome scanning for six loci on chromosome 4H are summarised in Figure 13.1. This chromosome was identified as carrying a gene for acid soil tolerance (Stølen and Andersen, 1978) so it is highly likely that one of these markers has a close association with the low pH tolerance gene. Scots Bere and Sprat Archer have the same allele at locus a) but differ from the other cultivars. At loci b) through d) Scots Bere has the most common allele that is present in Maythorpe, Ayr and Chime. Scots Bere has less common alleles at loci e) and f) and this suggests that these markers may have potential for marker assisted backcrossing. The development of this potential requires more precise mapping of low pH tolerance than was possible with morphological markers (Stølen and Andersen, 1978). The identification of closely linked markers will permit marker-assisted backcrossing, a process that is quicker and more precise than the conventional crossing and cultivar development procedures that were available in the 1970s.
Figure 13.1 Results from an experiment to assess genetic diversity in spring barley cultivars. SSR alleles at six loci (a-f) on chromosome 4H coded to indicate contrasts in allele size.
13.2 Genetic diversity within a crop has the potential to increase the overall biodiversity of the environment. Scots Bere, as a typical landrace, would not have been subject to the purification processes typical of the production of a modern cultivar. The need to prove that a new cultivar is Distinct, Uniform and Stable theoretically means that a National Listed cultivar is essentially a single genotype. During the SCRI genome scanning experiment, in which cultivars produced between 1890 and 1995 were genotyped, the effect of the 1964 Plant Varieties Rights Act was obvious in a rapid reduction in genetic diversity. A crop that is a single genotype is more amenable to modern agronomy giving economically worthwhile responses to high inputs but is also vulnerable to damage by pests etc. This may require intervention with pesticides that have unwanted side effects for species that are important for birds. Experimentation with cultivar mixtures indicates that mixing even a few genotypes improves performance under disease pressure (Newton et al, 1999).. The potential for landraces, whether natural or recreated, to improve overall biodiversity has not been tested so it is not possible to precisely estimate the effect of the reduction in use of Scots Bere.
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