PHYLOGENETIC-RELATIONSHIPS AMONG THE PINE STEM RUST FUNGI (CRONARTIUMAND PERIDERMIUM SPP.)

Species in Cronartium and its anamorphic genus Peridermium form a morp hologically homogeneous group of rust fungi that infect stems, branche s, and cones of Pints species in North and Central America, Asia, and Europe. Several species are important forest pathogens, causing severe economic and aesthetic damage to pines in forests and parks throughou t the northern hemisphere. Morphological characters have been used to distinguish among these rust fungi, but have proven inadequate for ass essing phylogenetic relationships within the group. In this study, we extracted fungal DNA from spores and infected host tissue representing collections of all major North American and Eurasian Cronartium and P eridermium species and of two related rust genera, Chrysomyxa and Pucc iniastrum. Using the polymerase chain reaction, we amplified and seque nced the internal transcribed spacer region from the nuclear ribosomal RNA genes, aligned sequences for all taxa, and generated phylogenetic trees using parsimony and neighbor-joining techniques. Parsimony anal ysis yielded a strict consensus of 24 trees that is congruent with the single tree generated by neighbor-joining analysis. Neighbor-joining was also used to compare trees derived from nucleotide sequences and f rom isozyme phenotype data from an earlier study; in general, the same species groups were supported in both data sets. Our analyses indicat e that the pine stem rust fungi form distinct clades that correlate wi th telial host families (e.g., Fagaceae and Santalaceae). Close phylog enetic relationships between autoecious, short-cycled Peridermium spec ies and putative heteroecious relatives were confirmed (e.g., P. harkn essii with C. quercuum f. sp. banksianae, and P. bethelii with C. coma ndrae). Nucleotide sequences and isozyme phenotypes were used to ident ify four undescribed taxa, including: California oak rust, which may b e a cone or gall rust that has become isolated from its aecial host; w hite-spored gall rust from the south western U.S., which was thought t o be an albino form of orange-spored P. harknessii; a previously undes cribed yellow-spored gall rust from California; and stalactiform limb rust of Jeffrey pine, which was thought to be a host-form of C. coleos porioides. In light of these results, a systematic reevaluation of Cro nartium and Peridermium morphology and biology is needed.