Abstract
Various types of data have been used for sampling plant core collections, including morphological, agronomic and ecogeographical traits, and molecular and biochemical markers. However, little is known about the ability of woody perennial core collections to retain the diversity and structure of the whole collection for characters that were not considered in the selection, especially when molecular markers are used. In this study, three core subsets were established for the apple germplasm bank curated at the Public University of Navarre (UPNa, Spain): based upon the diversity found with 10 SSR markers, another based upon the diversity assessed with 12 isozyme loci; and a third based upon morpho-agronomic diversity evaluated by 23 morpho-agronomic traits. Comparisons between these three subsets and to the whole collection were assessed to determine the impact of the data used in the selection on phenotypic and genetic diversity and on their population structure. The three subsets had a similar diversity and they did not differ from the original collection, according to Nei and Shannon-Weaver indices. The allelic/class frequencies were also always maintained in the three subsets. Overall, the kind of data used to constitute a core collection had little influence on the phenotypic and genetic diversity retained, so in the case of apple collections the use of molecular markers is preferable for this task because they allow a rapid and reliable characterization.
Highlights
The conservation of biodiversity can result in large collections that are difficult to characterize, evaluate, utilize and maintain
Molecular markers provide here a cost-feasible alternative that can be used on young, non-bearing trees, but nowadays the examples of the use of molecular markers to develop core collections in woody perennial species are yet restricted to few cases in apple (Laquidain et al, 2005; Volk et al, 2005), pear (Santesteban et al, 2008), table grapevine (Jiménez-Cantizano et al, 2008), cashew (Dhanaraj et al, 2002), sandalwood (Shashidhara et al, 2003) or cherimoya (Escribano et al, 2008)
Comparison between the whole collection and the core subsets revealed similar tendencies, no matter which data were originally used to create the subset: The mean allelic richness was of the same magnitude (14.5, 13.9 and 13.9 alleles per locus for the CS, CI and CM subsets), and all the frequent alleles were present in the three subsets
Summary
The conservation of biodiversity can result in large collections that are difficult to characterize, evaluate, utilize and maintain. To facilitate the characterization process, core subsets have been developed to represent the genetic diversity found within the entire collection (Brown, 1989). In the case of crops, core collections have been habitually obtained from passport, eco-geographical and morphological data (Balakrishnan et al, 2000; Grenier et al, 2000; Hu et al, 2000; Li et al, 2004), because these collections are usually very large (thousands of accessions) and the use of molecular markers in the entire collection is not feasible because of the cost (Grenier et al, 2000; Hu et al, 2000). Molecular markers provide here a cost-feasible alternative that can be used on young, non-bearing trees, but nowadays the examples of the use of molecular markers to develop core collections in woody perennial species are yet restricted to few cases in apple (Laquidain et al, 2005; Volk et al, 2005), pear (Santesteban et al, 2008), table grapevine (Jiménez-Cantizano et al, 2008), cashew (Dhanaraj et al, 2002), sandalwood (Shashidhara et al, 2003) or cherimoya (Escribano et al, 2008). Two important issues in the context of using molecular markers for constructing core collections could explain this
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