Hybridization in wild pear (Pyrus pyraster) from various regions in Germany and from Luxembourg with respect to Pyrus × communis

Pyrus pyraster is the prevailing native pear species in central Europe. The range of this forest tree species is comparatively large within the temperate zone. In most regions wild pear is very rare and considered to be seriously endangered. Thus, conservation of P. pyraster as part of the natural biodiversity is essential. The species may serve as a genetic resource in breeding programs, e.g., use of resistances existing in a wild species. A precondition for suitable conservation and breeding strategies is the identification of pure wild pears. Introgression from cultivated pears, supposed to be one major threat to the native gene pool, needs to be investigated. In total, 636 genotypes of P. pyraster and P. × communis were analysed. The 316 trees initially selected as P. pyraster originated from Germany (242) and Luxembourg (74). Pear trees growing in Germany belonged to populations in the states Rhineland-Palatinate (101), Saxony-Anhalt (120) and Saxony (21). A total of 320 cultivars, separated into old (238) and modern (82) categories, were provided by collections in Germany and Oregon/USA (NCGR, Corvallis). Accessions have been typed for eight polymorphic isozyme loci. A model-based Bayesian clustering approach was applied to all multilocus genotype data. Wild and cultivated pear trees made up two different gene pools but could not be distinguished very clearly by nuclear markers. However, modern cultivars appeared to be distinct from all other subgroups. The discrimination between 'wild' and 'cultivated' was less obvious than in European apples. The genetic result might be expected when following the evolutionary hypothesis that P. pyraster is one primary progenitor of European cultivars. Morphologically wild pears from natural sites and old cultivars looked quite different. The extent of hybridization between the two major gene pools investigated is hard to assess.