Breeding of multipurpose willows on the basis of Salix daphnoides Vill., Salix purpurea L. and Salix viminalis L.

Willows are planted in short rotation coppices (SRC) to produce biomass. Another potential use of willows is the extraction of natural salicylates as alternatives to chemically synthesized acetyl salicylic acid (medical use). Available clones in Europe based on Salix viminalis L. do not contain salicylates and have high water requirements. In order to breed willows that can serve both as bioenergy and salicylate source under dry soil conditions, a collection of several hundred wild type genotypes of Salix daphnoides Vill. and Salix purpurea L. was used for an extensive crossing program with selected S. viminalis biomass clones. Altogether 578 inter- and intraspecific crossings resulted in 203 progenies and 622 genotypes. After selection in nursery trials 62 genotypes have been cloned and planted into two field trials with different soil moisture. Crossings of salicylate free S. viminalis clones with salicylate containing S. daphnoides and S. purpurea clones resulted in progenies that contained both salicylate and triandrin (from S. viminalis). The highest salicylate contents were found in S. daphnoides x daphnoides crosses followed by S. viminalis x daphnoides and S. purpurea x viminalis. Rust infection was low for almost all genotypes. While at the wet site the highest biomass was recorded for S. viminalis clones, the highest biomass at the dry soil site was recorded for S. daphnoides x daphnoides clones. This shows that it is possible to produce clones with high biomass and high salicylate content by intraspecific crossings of S. daphnoides. Because of the different cutting regimes at the two sites (first year cut at the dry site, no first year cut at the wet site), further investigations are necessary to confirm the superiority of S. daphnoides clones over S. viminalis clones at dry sites.