AFLP based alternatives for the assessment of Distinctness, Uniformity and Stability of sugar beet varieties
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Three approaches for addressing criteria for Distinctness, Uniformity and Stability (DUS) assessment by means of AFLP data are presented. AFLP data were obtained for three consecutive seed deliveries of 15 sugar beet varieties that were under investigation for the official Belgian list (’93, ’94 and ’95). In total, 696 AFLP markers were scored on 1350 plants. As a first approach, a cluster analysis based on Nei’s standard genetic distances between varieties and/or seed deliveries was made. Three major groups put together varieties belonging to corresponding breeding programmes. Statistical procedures, involving bootstrapping and random sampling of subsets of markers, were applied to test the reproducibility of the ordinations and the redundancy present in the data set. In a second approach, the genetic structure inferred by varieties and seed deliveries was submitted to an Analysis of Molecular Variance (AMOVA). Major genetic variation was attributed to individual plant differences within seed deliveries. Differences among seed deliveries seemed to be as important as differences among varieties or breeding programmes. Individual plant data were used for assignment tests. The computation of the assignment was based on the ranking of individual genotypes to one other (based on Jaccard similarity coefficients). The distribution over the accessions for each variety or seed delivery was used to check what group of plants each individual is genetically most similar to. Varieties were classified according to the degree to which the distribution over the different accessions was mainly allocated to their appropriate seed deliveries (from the same variety) or cross- allocated to other varieties. Criteria for DUS-evaluation could be set by each of the approaches; it is discussed in what way the result obtained differs and agrees.
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