Molecular evidence indicates that subarctic willow communities in Scotland support a diversity of host-associated Melampsora rust taxa Jeremy M. MILNE a , Stephan HELFER a, *, Calum KIRK b , Peter M. HOLLINGSWORTH a , Richard A. ENNOS b a Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK b Institute for Evolutionary Biology, University of Edinburgh, Kings Buildings, Ashworth Laboratories, West Mains Road, Edinburgh EH9 3JT, UK article info Article history: Received 8 September 2011 Received in revised form 8 February 2012 Accepted 27 February 2012 Available online 3 March 20123 March 2012 Corresponding Editor: Kentaro Hosaka Keywords: ITS Melampsora Phylogeny Salix Subarctic willow abstract Rare and threatened subarctic willow scrub communities in the UK are the subject of ongoing conservation programmes, yet little is known about the diversity of fungal taxa that they support. Isolates of the rust genus Melampsora were sampled from 112 leaves of eight subarctic willow (Salix) taxa and their hybrids from twelve sites in the UK. In order to determine the number of Melampsora taxa present in the samples, isolates were sequenced for the Internal Transcribed Spacer (ITS) region of rDNA and data were subject to phylogenetic analysis. Maximum likelihood and Bayesian analysis indicated that the iso- lates fell into three strongly supported host-associated clades. Clade I contained only iso- lates from Salix herbacea and was distinguished morphologically by dense urediniospore echinulation and thin cell walls. Clade II contained isolates from Salix arbuscula and Salix reticulata only. These could not be distinguished morphologically from isolates in Clade III which were found on Salix lapponum, Salix myrsinites, Salix myrsinifolia, Salix aurita, Salix lanata, and their hybrids. Clade II was most distinct in ITS sequence, differing by 50 bases from Clades I and III, while the latter clades differed in sequence by only 24 bases on aver- age. Clades I and III are likely to represent the previously recognised taxa Melampsora alpina Juel 1894 and Melampsora epitea Th€ um. 1879 respectively, but Clade II has not apparently been described before. Significant differences in the intensity of infection by isolates of Clade III were found among different Salix species at a single site, suggesting either differ- ences in resistance among Salix taxa, or the presence of further cryptic taxa within Clade III. The study illustrates the power of molecular phylogenetic analysis to reveal cryptic bio- diversity within Melampsora, and suggests that conserving Salix host diversity within sub- arctic willow communities will ensure that a diversity of associated Melampsora taxa is maintained. ª 2012 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: þ44 1312482865; fax: þ44 1312482901. E-mail addresses: s.helfer@rbge.ac.uk, s.helfer@rbge.org.uk journal homepage: www.elsevier.com/locate/funbio fungal biology 116 (2012) 603 e612 1878-6146/$ e see front matter ª 2012 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.funbio.2012.02.008