Characterisation of genetic diversity in potential biomass willows (Salix spp.) by RAPD and AFLP analyses

The genus Salix (willow) contains a number of species which have great pote ntial value as biomass crops in short rotation coppice (SRC). Efforts to im prove biomass willows by breeding are currently hampered by the limited inf ormation available on genetic diversity and on genetic relationships within and among species, clones, and hybrids in the gene pool. Hybridisation occ urs commonly in nature and the relatedness of many clones is unclear. Molec ular markers were used to assess genetic diversity in a reference set of wi llows maintained within the U.K. National Collection and 16 elite clones cu rrently being evaluated in field trials at several European sites. The two marker systems tested, RAPDs and AFLPs, were equally informative for reveal ing relationships within the reference set of clones. No differences were o bserved when alternative similarity coefficients were compared or when anal ysis was restricted to the use of polymorphic bands only. Good agreement wi th available knowledge of the clonal origins was obtained and one instance of duplicate clones was identified. AFLPs revealed more genetic diversity a nd discriminated between closely related clones. A difference in the relati onships revealed was observed with one AFLP primer combination. RAPDs were more problematic, both in terms of reproducibility and scorability.