Sequence variation and geographic distribution of pseudoflower-forming rust fungi (Uromyces pisi s. lat.) on Euphorbia cyparissias

To attract insects for sexual reproduction, some fungi can induce the forma tion of pseudoflowers on their hosts. Pseudoflowers are rosettes of yellow host leaves upon which the fungus presents gametes in sweet nectar. Eleven species of the fungus complex Uromyces pisi can induce pseudoflowers on the host Euphorbia cyparissias. The taxonomy of these species is based on the choice of the alternate host, a species of Fabaceae, as well as on teliospo re morphology on the Fabaceae hosts. Morphological identification of the fu ngi on E. cyparissias is impossible. To identify the fungal species on infe cted E. cyparissias, we compared sequences from the ITS region of the rDNA to the DNA from five identified fungal species on Fabaceae. From 43 specime ns on E. cyparissias, collected in 1997-99 in Switzerland, 24 specimens cou ld be identified as U. pisi s. str. and 16 specimens as U. striatus. Two sp ecimens were identified as U. laburni and U. loti, respectively, and one sp ecimen could not be identified. We therefore conclude that fungal pseudoflo wers are typically induced by U. pisi s. str. on U. striatis in Switzerland , although other species do sometimes occur. The ITS sequences were then us ed to reconstruct the phylogenetic relationship among species in the U. pis i complex and two closely related microcyclic rust species of the complex U romyces scutellatus. Phylogenetic analyses indicated that the microcyclic s pecies may be descendants from macrocyclic U. pisi s.l. ancestors. The ITS region sequenced in this study was found to be appropriate for answering ph ylogenetic, as well as ecological questions, and provided valuable markers for future studies.