Host-pathogen relationship between <em>Salix</em> and <em>Melampsora</em> sheds light on the parentage of some biomass willows.

The association between willow (Salix) and rust (Melampsora) is highly specific. Willows named Salix burjatica, S. dasyclados (S. × dasyclados) and S. × 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 from hybridization between. S. caprea, S. viminalis and S. cinerea. In the present work, 59 willow clones were investigated through morphological examination and detached leaf inoculation using willow differentials, for their association, in southwest England, with M. capraearum and three pathotypes of 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 clones; Me-B on wild S. cinerea, S. × calodendron, S. × dasyclados'De Biardii 445' and S. 'Spaethii'; Me-C on all S. burjatica clones and most S. × dasyclados clones. Both M. caprearum and Me-A infected all S. × sericans (S. caprea × viminalis) clones and S. × dasyclados'LA041/03'. We suggest that S. × dasyclados'LA041/03' should be treated as S. × sericans (S. caprea × S. viminalis); S. burjatica, S. dasyclados and S. × dasyclados as synonyms; S. × dasyclados 'De Biardii 445' as S. × calodendron 'De Biardii 445'; and S. 'Spaethii' as S. × calodendron 'Spaethii'. [ABSTRACT FROM AUTHOR]