Genetic variability among European Ash (Fraxinus excelsior L.) and Sycamore (Acer pseudoplatanus l.) populations in North-Western Italy The genetic diversity and differentiation among 15 populations of European Ash and 18 of Sycamore were studied by means of isozyme variation. Populations were chosen on the basis of a possible inclusion in the official Italian List of Seed Stands. Proteins were extracted by winter buds collected from at least 75 non-adjacent plants, chosen at random over a 2-3 ha area. Genetic variability was estimated through the following parameters: expected proportion of heterozygotes (He), average number of alleles per locus (N), effective number of alleles per locus (Ne), percentage of polymorphic loci (P). The excess or deficiency of heterozygotes was estimated by calculating the fixation index (FIS), while the genetic differentiation among populations were estimated by partitioning the total gene diversity (HT), in gene diversity within populations (HS) and among populations (DST); the relative degree of genetic differentiation (GST) was calculated as DST/HT. It was possible to separate variants for 10 enzyme systems, all polymorphic within the studied material: 11 genetic loci were scored in European Ash and 12 in Sycamore. Allele frequencies showed to be similar in different populations, with the exception of locus Mnr-A in European Ash, where the more frequent allele differed according to populations. In European Ash, the expected heterozygosity ranged from 0.127 to 0.332 with an average of 0.206; the mean number of alleles per locus was 2.7 (range 2.3-2.9), the effective number of alleles per locus 1.3 (1.2-1.6) and the percentage of polymorphic loci always 100. Fixation index ranged from -0.097 to 0.047 with an average of -0.025, showing a slight excess of heterozygotes. In Sycamore, the values were as follows: He 0.200 (range 0.125-0.284), N 2.7 (2.4-3.0), Ne 1.3 (1.2-1.5), P 93.5 (83.3-100); FIS was on average -0.069 (range from -0.257 to 0.109) and showed a more clear heterozygotes excess. Only 5 and 3.4% (respectively for European Ash and Sycamore) of the total genetic diversity was due to differentiation among populations and the mean value of Nei's genetic distance was 0.012 for European Ash and 0.007 for Sycamore. Therefore the studied populations share same gene pools and no barriers hamper the gene flow. The results of the study provide useful information for in situ preservation of forest biodiversity. Furthermore, the obtained data can be used for the identification of the most valuable stands for the production of high quality seeds.
Variabilità genetica in popolazioni di frassino e acero di monte dell'Italia settentrionale
BELLETTI, Piero;MONTELEONE, Ignazio
2000-01-01
Abstract
Genetic variability among European Ash (Fraxinus excelsior L.) and Sycamore (Acer pseudoplatanus l.) populations in North-Western Italy The genetic diversity and differentiation among 15 populations of European Ash and 18 of Sycamore were studied by means of isozyme variation. Populations were chosen on the basis of a possible inclusion in the official Italian List of Seed Stands. Proteins were extracted by winter buds collected from at least 75 non-adjacent plants, chosen at random over a 2-3 ha area. Genetic variability was estimated through the following parameters: expected proportion of heterozygotes (He), average number of alleles per locus (N), effective number of alleles per locus (Ne), percentage of polymorphic loci (P). The excess or deficiency of heterozygotes was estimated by calculating the fixation index (FIS), while the genetic differentiation among populations were estimated by partitioning the total gene diversity (HT), in gene diversity within populations (HS) and among populations (DST); the relative degree of genetic differentiation (GST) was calculated as DST/HT. It was possible to separate variants for 10 enzyme systems, all polymorphic within the studied material: 11 genetic loci were scored in European Ash and 12 in Sycamore. Allele frequencies showed to be similar in different populations, with the exception of locus Mnr-A in European Ash, where the more frequent allele differed according to populations. In European Ash, the expected heterozygosity ranged from 0.127 to 0.332 with an average of 0.206; the mean number of alleles per locus was 2.7 (range 2.3-2.9), the effective number of alleles per locus 1.3 (1.2-1.6) and the percentage of polymorphic loci always 100. Fixation index ranged from -0.097 to 0.047 with an average of -0.025, showing a slight excess of heterozygotes. In Sycamore, the values were as follows: He 0.200 (range 0.125-0.284), N 2.7 (2.4-3.0), Ne 1.3 (1.2-1.5), P 93.5 (83.3-100); FIS was on average -0.069 (range from -0.257 to 0.109) and showed a more clear heterozygotes excess. Only 5 and 3.4% (respectively for European Ash and Sycamore) of the total genetic diversity was due to differentiation among populations and the mean value of Nei's genetic distance was 0.012 for European Ash and 0.007 for Sycamore. Therefore the studied populations share same gene pools and no barriers hamper the gene flow. The results of the study provide useful information for in situ preservation of forest biodiversity. Furthermore, the obtained data can be used for the identification of the most valuable stands for the production of high quality seeds.
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