Nuclear cyp73 intron fragment length polymorphism supports morphological analysis of Salix species and hybrids

Abstract

The polyploid Salix alba L.–Salix fragilis L. hybrid complex still presents major difficulties in morphological identification. Most of the measured characters show a low diagnostic value for unambiguously identifying the parental species and their hybrid Salix × rubens Schrank due to continuous variation creating a large overlap in leaf and catkin morphology. Fragment length polymorphism of nuclear cyp73 intron markers was used to identify species and hybrids. This multilocus genotyping could be applied in a morphological analysis of trees from hybrid zones and allowed to demonstrate that morphological features of leaves and catkins clearly separated S. alba from S. fragilis. The hybrid individuals largely overlapped with both parental species but appeared to be morphologically more similar to S. fragilis than to S. alba. Cyp73 analysis of 11 Salix taxa revealed intermediate positions of two hybrid taxa with S. alba, namely S. × rubens and S. × sepulcralis Simonkai with their respective parental species S. fragilis and S. babylonica L. Additionally, the cyp73 intron multilocus genotypes clustered tetraploid taxa separately from diploid willows. Cyp73 introns are valuable markers for fast, reliable and straightforward genotyping in willow species and hybrids.

Keywords:

• Salix alba
• Salix fragilis
• Salix babylonica
• leaf morphology
• male catkins
• female catkins
• cyp73 intron

Acknowledgements

This research was financed by the EU‐QLKR‐CT‐2000‐30227 contract (DYNAMO), the Fund for Scientific Research Flanders (KN 1.5124.03) and the Vrije Universiteit Brussel (OZR 965). We thank Dr. Heike Beismann for field assistance in collecting reference trees in a hybrid zone and Prof. G. Angenon (VUB‐PLAN) for laboratory services.