Abstract
Willows are cultivated worldwide because of its ecological, economical and social importance. Melampsora species, causal agents of rust diseases, are the most widespread and invasive pathogens occurred on willow cultivars. In China, approximately 25 Melampsora species have been reported on willows. The current classification is mainly based on morphological characters of uredinial and telial stages and host range. However, species concepts for willow Melampsora species remain confused, and hence their species identification is difficult. In this study, herbarium specimens, which were collected from various willow cultivars and locations of China, were used for morphological and molecular evaluation. Phylogenetic trees were constructed based on rDNA large subunit D1/D2 region and the internal transcribed spacers ITS1, ITS2 and 5.8S sequence data and compared with traditional morphological classification. In the combination of D1/D2 regions and ITS regions sequences, eight highly supported clades were obtained. Molecular phylogeny supported taxonomic identity of M. larici-pentandrae . Melampsora epiphylla , M. kiusiana , M. humilis and M. chelidonii-pierotii were scattered into different clades, respectively. Morphological characteristics of these species among different clades correlated with dimension of urediniospores and teliospores, structures of spine and paraphysis. Meanwhile, taxonomic identity of M. arctica , M. epiphylla , M. kiusiana , M. humilis and M. chelidonii-pierotii , M. tsinlingensis and M. kimikotica could not be supported based on rDNA phylogeny. Therefore, taxonomic revision of Melampsora species on willows is needed.
