Taxonomic study of stripe rust, Puccinia striiformis sensu lato, based on molecular and morphological evidence

Phylogenetic analyses of ITS and β-tubulin DNA sequences for 30 Puccinia striiformis specimens from wide geographic and host ranges revealed four strongly supported monophyletic lineages. Based on comparisons of morphological characteristics, and after consideration of previous classifications, the lineages were recognized as P. striiformis sensu stricto, Puccinia pseudostriiformis, Puccinia striiformoides and one new species, Puccinia gansensis. A new series (Puccinia Series Striiformis) was erected to accommodate this strongly supported monophyletic group of four species within Puccinia. Expanded descriptions, illustrations and a tabular identification key are provided. The morphological differences among species are subtle but host association and combinations of other characters can be used successfully for identification. Puccinia striiformis s.str. has the widest host range, within the tribe Triticeae (Aegilops, Elymus, Hordeum and Triticum) but it is less diverse than previously documented. The other three species are restricted to single genera in Poeae (P. pseudostriiformis on Poa; P. striiformoides on Dactylis) or Stipeae (P. gansensis on Achnatherum). Urediniospore size and surface echinulation, especially as seen by SEM, germ pore number, shape of uredinial paraphyses, and teliospore hilum width were the main features used to differentiate species. Relying solely on the symptom of linearly aligned uredinia on chlorotic stripes on leaves, from which the common name "stripe rust" was derived, is not recommended because sori of other leaf rust species may also form in a linear series.