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average and low inbreeding coefficient was not statistically significantly different from zero. By all analysed indices, seed stand Grofija is suitable for collection of forest reproductive material.
Population Razpotje is not an appropriate candidate for a seed stand because all indices used to describe genetic diversity were under the Slovenian average. Lower genetic diversity of this population is probably the reason for statistically significant differentiation from other populations (Table 3), although the same differentiation was not observed with genetic distances. Most likely explanation for the observed properties is the placement of the stand, which was located alongside a water stream and was longer than wider compared to other populations with more or less equal width and length of the stand.
According to the analysis of five microsatellite loci, the seed stand of non-autochthonous origin Rodik (which was presumably planted with seedlings from the neighbouring stands), does not differ from other analysed stands (except from the stand Razpotje based on the pair-wise FST values). Its origin is therefore most likely within the same gene pool as the remaining four populations or at least within the studied range of common ash, as was assumed at the time of its approval (The Slovenian national... 2010). Whether the gene pool is limited to the studied range remains open. One way of verifying the borders of the gene pool is to compare alleles from our study to the ones in the existing studies in at least northern Italy and Bosnia with the help of positive controls used during laboratory procedures, sizing and genotyping. If no adaptive differences are discovered, transfer of forest reproductive material within the same gene pool is possible, even if it extends beyond Slovenian borders. Also, mixing of seed lots from different approved seed stands, or from the same seed stand, produced in different ripening years, might be considered for improving of genetic diversity; however, caution would be needed to avoid including hybrids or seeds from related species, or seeds with reduced genetic diversity (Valadon 2009). All mixing is subjected to an official control of the share of original seed lots.
Based on the results of this study, analysed populations are genetically similar, at least when neutral variation is considered. No obstacle to liberal transfer of forest reproductive material in western and central Slovenia is therefore present. It must be however noted that in the present study no adaptive traits were analysed. Additionally, individuals with intermediate signs between common and narrow-leaved ash were observed in ash stands in the Sub-Pannonian region (Jarni 2009, Westergren 2010). These were not included in the here presented genetic analysis. In the light of possible hybrids in this region, it is strongly advised to consider each case individually, before taking the decision of transferring common ash forest reproductive material be­tween Sub-Pannonian and other Slovenian provenance or ecological regions. Apart from potential hybrids, selection of site appropriate provenances is necessary also because common ash from riparian forests is more tolerant to waterlogging than common ash from mountainous environment, indicating genetic adaptation to a reduction of oxygen in common ash from riparian forests (Jaeger et al. 2009). The same study also showed that net assimilation of narrow-leaved ash (Fraxinus angustifolia Vahl), a species with higher flooding tolerance than common ash, remained unaffected during waterlogging, while slight reduction was observed for riparian provenance and a strong one for mountainous provenance.
Overall pattern of nuclear genetic diversity of the studied populations of common ash in Slovenia gives a picture of high diversity belonging to a single gene pool. Based on the analysis of five microsatellite loci, no restrictions for transferring forest reproductive material within the studied range (western, south-western and central Slovenia) can be put forward. However, forest reproductive material from seed stand Rodik should be collected in a way that ensures its wide genetic base.
The project was financed through research programme P4-0107, a young researchers’ project (MW) and research projects L4-9647, L4-4450, V4-0372, V4-0353 and V4-1140 by the Slovenian Research Agency and co-financed by the Ministry for Agriculture, Forestry and Food.
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