USE OF RAPD MARKERS TO ESTIMATE HYBRIDIZATION IN SALIX ALBA AND SALIXFRAGILIS

The polyploid Salix alba - Salix fragilis hybrid complex is rather dif ficult to study when using only morphological characters. Most of the features have a low diagnostic value for identifying the hybrids, intr ogression patterns and population genetic structure. Molecular data fr om isozymes and random amplified polymorphic DNA's (RAPD) previously h ave been investigated in several case studies on willows from Belgium. A thorough screening with 16 decamer primers for PCR based polymorphi sm revealed 95 amplification products at the species level. On the bas is of genetic distances, clustering and ordination analysis, a referen ce system for identification of clones has been established. The propo sed reference system was previously checked against additional Europea n samples of putative pure species to ensure its reliability and is cu rrently applied to elucidate patterns of hybridization on a regional s cale as well as on a local scale, this in the context of conservation genetics. The RAPD analysis suggests that hybridization is not a domin ating process and that both species have kept their gene pools well se parated.