Host-pathogen relationship between Salix and Melampsora sheds light on theparentage of some biomass willows

The association between willow (Salix) and rust (Melampsora) is highly spec ific. Willows named Salix burjatica, S. dasyclados (S. x dasyclados) and S. x calodendron are important in renewable-energy plantations in the UK and western Europe. There has been much controversy over their origin, species status and nomenclature. It has been suggested that they have originated fr om hybridization between. S. caprea, S. viminalis and S. cinerea. In the pr esent work, 59 willow clones were investigated through morphological examin ation and detached leaf inoculation using willow differentials, for their a ssociation, in southwest England, with M. capraearum and three pathotypes o f Melampsora epitea (Me-A, B and C). M. capraearum was found on all clones of S. caprea and its hybrids with S. aurita; Me-A on all S. viminalis clone s; Me-B on wild S. cinerea, S. x calodendron, S. x dasyclados 'De Biardii 4 45' and S. 'Spaethii'; Me-C on all S. burjatica clones and most S. x dasycl ados clones. Both M. coprearum and Me-A infected all S. x sericans (S. capr ea x viminalis) clones and S. x dasyclados 'LA041/03'. We suggest that S. x dasyclados 'LA041/03' should be treated as S. x sericans (S. caprea x S. v iminalis); S. burjatica, S. dasyclados and S. x dasyclados as synonyms; S. x dasyclados 'De Biardii 445' as S. x calodendron 'De Biardii 445'; and S. 'Spaethii' as S. x calodendron 'Spaethii'.