Molecular approach of genetic affinities between wild and ornamental Platanus

Abstract

Apart from the wild species P. orientalis and P. occidentalis, the cultivated plane trees constitute a wide and heterogeneous group, with uncertain genetic status and largely debated names. The recent canker stain problem in Europe makes it necessary at the present time to consider the genetic resources and to determine the genetic bases of all these trees. To attain this objective, a genetic molecular approach was used to analyze 60 trees of P. orientalis and P. occidentalis, different London planes (P. hispanica and P. densicoma), a few controlled P. occidentalis x P. orientalis hybrids and particular trees from arboreta and old parks. Molecular analysis involved thirty RAPD fragments generated with nine primers, PCR-RFLP in the 5S RNA genes and mitochondrial polymorphisms revealed by RFLP method. Clones were recognized among P. hispanica and P. densicoma trees. A Correspondence Analysis and a dendrogram constructed according to the genetic distances confirmed the supposed hybrid origin of P. hispanica and P. densicoma between P. occidentalis and P. orientalis. Contribution of P orientalis to their constitution seems more important than that of P. occidentalis. Mitochondrial DNA polymorphisms indicated that crosses occurred in both directions. Moreover, P. occidentalis as female parent led to P. densicoma whereas P. orientalis as female parent led to P. hispanica. Low prevalence of pure species individuals and confusion risks with hybrid trees even for old trees are highlighted.