Crown rust fungi with short lifecycles – the Puccinia mesnieriana species complex


Hambleton S., Liu M., Eggertson Q., Wilson S., Carey J., Anikster Y., Kolmer J. 2019. Crown rust fungi with short lifecycles – the Puccinia mesnieriana species complex. Sydowia 71:47-63

Plain language summary

The lifecycles of rust fungi range from being highly complex (macrocyclic) with two alternating plant hosts and producing up to five morphologically different types of spores, to highly reduced (microcyclic) on one host with only one type of spores observed (teliospores). Close relationships between specific species with such markedly different lifecycles have been hypothesized in the literature. This study tested the hypothesis that Puccinia mesnieriana (microcyclic), causing diseases on Rhamnus (Buckthorn), is closely related to the species that causes crown rust of oats (Puccinia coronata), which produces similar morphologically distinctive teliospores on grasses and has an alternating host in Rhamnus. This study examined historic herbarium specimens archived in four international collections. Phylogenetic analyses of DNA sequences for two gene regions, ITS-28S and COI, showed that the species Puccinia mesnieriana as traditionally understood was a complex of four distinct species. The four species have differentiating morphological characteristics, host associations and geographic distributions. Based on the provenance of the collections studied, P. mesnieriana was found to be restricted to Portugal and a new species, Puccinia pseudomesnieriana, was described for all specimens sampled from other parts of the Mediterranean region. Specimens from California USA were separated into two well-supported lineages. One was recognized as P. digitata, a species that had been long considered a synonym of P. mesnieriana. The other was recognised as a new species, Puccinia pseudodigitata. The two North American species are more closely related to each other than to the Mediterranean species. Although all four species are distinct from Puccinia coronata, they are members of the same large species complex known as Puccinia Series Coronata, confirming the original hypothesis.


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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