characteristic, the more the difference contributes to the GAIA distance. Only differences that are equal or larger than the minimum distance required for each individual characteristic are included. 1.4.2 Molecular distance The molecular distance component is computed on the differences observed on a set of markers. Different types of molecular markers and distances can be used. In the case of the study done in France on maize, 60 SSR markers and Roger’s distance have been used. It is important that sufficient markers, with a good distribution on the chromosomes, are used. The type of markers, the effect of the number of markers and the distribution of the markers need to be considered according to the species concerned. 1.4.3 Before combining these two components, an evaluation of the link between molecular distance and a global assessment of distinctness by a panel of experts needs to be done on a set of pairs of varieties. In the case of maize, that evaluation was made on the following basis: Material: 504 pairs of varieties tested in parallel with molecular markers Field design: pairs of varieties grown side by side (1 plot = 2 rows of 15 plants) Visual assessment by maize crop experts: Scale of similarity: 1. the two varieties are similar or very close 3. the two varieties are distinct but close 5. the comparison was useful, but the varieties are clearly distinct 7. the comparison should have been avoided because the varieties are very different 9. the comparison should have been avoided because the varieties are totally different (“even” notes are not used in the scale) In the case of maize, this evaluation showed that no parental lines with a molecular distance greater than 0.15 were considered as similar or very close by a DUS expert evaluation (see Figure 2). Figure 2 1.4.4 On the basis of that result, the combination of morphological and molecular distances offers the possibility to establish a decision scheme as follows (see Figure 3). Use of SNP molecular markers doesn’t modify this scheme. Figure 3 1.4.5 No pairs of varieties with a molecular distance larger than 0.2 were visually assessed by maize crop experts as those which required another year of growing trial (see Figure 4). Figure 4 1.4.6 This study provides empirical proof that there is presumably no risk in applying an additional molecular threshold in the zone GAIA < 2. This Additional threshold would reduce significantly the number of
characteristic, the more the difference contributes to the GAIA distance. Only differences that are equal or larger than the minimum distance required for each individual characteristic are included. 1.4.2 Molecular distance The molecular distance component is computed on the differences observed on a set of markers. Different types of molecular markers and distances can be used. In the case of the study done in France on maize, 60 SSR markers and Roger’s distance have been used. It is important that sufficient markers, with a good distribution on the chromosomes, are used. The type of markers, the effect of the number of markers and the distribution of the markers need to be considered according to the species concerned. 1.4.3 Before combining these two components, an evaluation of the link between molecular distance and a global assessment of distinctness by a panel of experts needs to be done on a set of pairs of varieties. In the case of maize, that evaluation was made on the following basis: Material: 504 pairs of varieties tested in parallel with molecular markers Field design: pairs of varieties grown side by side (1 plot = 2 rows of 15 plants) Visual assessment by maize crop experts: Scale of similarity: 1. the two varieties are similar or very close 3. the two varieties are distinct but close 5. the comparison was useful, but the varieties are clearly distinct 7. the comparison should have been avoided because the varieties are very different 9. the comparison should have been avoided because the varieties are totally different (“even” notes are not used in the scale) In the case of maize, this evaluation showed that no parental lines with a molecular distance greater than 0.15 were considered as similar or very close by a DUS expert evaluation (see Figure 2). Figure 2 1.4.4 On the basis of that result, the combination of morphological and molecular distances offers the possibility to establish a decision scheme as follows (see Figure 3). Use of SNP molecular markers doesn’t modify this scheme. Figure 3 1.4.5 No pairs of varieties with a molecular distance larger than 0.2 were visually assessed by maize crop experts as those which required another year of growing trial (see Figure 4). Figure 4 1.4.6 This study provides empirical proof that there is presumably no risk in applying an additional molecular threshold in the zone GAIA < 2. This Additional threshold would reduce significantly the number of
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