Crown rust fungi with short lifecycles – the Puccinia mesnieriana species complex
The short lifecycle rust species Puccinia mesnieriana produces telia and teliospores on buckthorns (Rhamnus spp.) that are similar to those produced by the crown rust fungi (Puccinia Series Coronata) on oats and grasses. The morphological similarity of these fungi led to hypotheses of their close relationship as correlated species. Phylogenetic analyses based on ITS2 and partial 28S nrDNA regions and the cytochrome oxidase subunit I (COI) revealed that P. mesnieriana was a species complex comprising four lineages within P. Series Coronata. Each lineage was recognized as a distinct species with differentiating morphological characteristics, host associations and geographic distribution. Puccinia mesnieriana was restricted to a single specimen from Portugal which was morphologically similar to and shared the same provenance as the type specimen of the species, which was not sequenced. Puccinia pseudomesnieriana sp nov., included all other specimens sampled from the Mediterranean region and was closely related to P. coronati-brevispora and P. coronati-longispora. Specimens from California USA formed a monophyletic group comprising two well-supported lineages recognized as P. digitata, long considered a synonym of P. mesnieriana, and P. pseudodigitata sp nov. Descriptions, illustrations and a tabular key are provided for these four microcyclic rust pathogens of Rhamnus.
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