Different evolutionary histories of two Phragmidium species infecting the same dog rose hosts 1 Christiane M. RITZ 1 *, Wolfgang F. A. MAIER 2 *#, Franz OBERWINKLER 2 and Volker WISSEMANN 1 1 Friedrich-Schiller-Universita ¨t Jena, Institut fu ¨r Spezielle Botanik, Philosophenweg 16, D-07743 Jena, Germany. 2 Eberhard-Karls-Universita ¨t Tu ¨bingen, Lehrstuhl fu ¨r Spezielle Botanik und Mykologie, Auf der Morgenstelle 1, D-72076 Tu ¨bingen, Germany. E-mail : christiane.ritz@uni-jena.de Received 29 December 2004; accepted 3 March 2005. Rust fungi in the genus Phragmidium are frequent pathogens of both wild and cultivated roses. We investigated the occurrence and relationships of rusts on dog roses, Rosa sect. Caninae (Rosa canina, R. corymbifera and R. rubiginosa) in Germany. Two Phragmidium species, P. mucronatum and P. tuberculatum, were able to infect each of the three dog rose species examined. However, the overall infection of R. rubiginosa was significantly lower, which could be important for rose breeding. Despite overlapping host ranges, the evolutionary background of P. tuberculatum and P. mucronatum is quite distinct. Phylogenetic analyses of the D1/D2 region of the LSU rDNA suggest that P. mucronatum shares a common ancestor with other rose rusts, whereas P. tuberculatum evolved from a Rubus-Sanguisorba rust clade and must have undergone a host shift to Rosa spp. INTRODUCTION The predominantly Northern Hemisphere rust genus Phragmidium comprises about 60 species (Cummins & Hiratsuka 2003). Phragmidium species, like the entire family Phragmidiaceae, have an autoecious life-cycle and are restricted to rosaceous hosts, with only two documented exceptions from the USA (Peterson & Cronin 1967). On dog roses four Phragmidium species can be found in Central Europe, viz. P. fusiforme, P. mucronatum, P. tuberculatum, and P. rosae- pimpinellifoliae. However, the taxonomic history of many species is rather complex (Dietel 1905a, b) and especially the Phragmidium species on roses, ‘Form- enkreis Phragmidium mucronatum ’, were said to have overlapping morphological characters (Ga¨ umann 1959). This casts doubt onto the broad host ranges stated for P. mucronatum and P. tuberculatum since these species could have been misidentified due to excessively broad morphological species concepts (cfr Newcombe 2003). The Eurasian dog roses (Rosa sect. Caninae) are a morphologically and genetically highly diverse group, about 30 species of which can be found in Central Europe (Kla´ sˇ tersky` 1969, Henker & Schulze 1993). Their most striking feature is a unique meiotic behav- iour, the so-called ‘Canina-meiosis’ (Ta¨ ckholm 1920, 1922), where the pentaploid genome is distributed unequally during meiosis resulting in haploid pollen grains and tetraploid egg cells. After fertilization, the pentaploid state is restored and results in full sexual reproduction (Wissemann & Hellwig 1997). We investigated which rust species can be found on the three most common dog rose species in Germany (Rosa canina, R. corymbifera, and R. rubiginosa). We examined the frequency of the occurring rusts and whether these rust species show any infection pre- ference for a particular rose host. By means of mol- ecular phylogenetic analyses based on nrLSU sequence data we tested whether the morphological species determinations proved valid and whether there is any correlation between specific host infection and pathogen phylogeny. MATERIALS AND METHODS Sampling and collection Three species of dog roses differing in leaf sur- face characters were investigated, i.e. R. canina with glabrous leaves, R. corymbifera with hairy leaves, and 1 Dedicated to John Webster on the occasion of his 80th birthday. * Corresponding author. The first two authors contributed equally to the paper. # Present address: Department of Genetics, FABI, University of Pretoria, Pretoria 0002, South Africa. Mycol. Res. 109 (5): 603–609 (May 2005). f The British Mycological Society 603 doi:10.1017/S0953756205002844 Printed in the United Kingdom.