Ustilago species causing leaf-stripe smut revisited

Abstract

Leaf-stripe smuts on grasses are a highly polyphyletic group within Ustilaginomycotina, occurring in three genera, Tilletia, Urocystis, and Ustilago. Currently more than 12 Ustilago species inciting stripe smuts are recognised. The majority belong to the Ustilago striiformis-complex, with about 30 different taxa described from 165 different plant species. This study aims to assess whether host distinct-lineages can be observed amongst the Ustilago leaf-stripe smuts using nine different loci on a representative set. Phylogenetic reconstructions supported the monophyly of the Ustilago striiformis-complex that causes leaf-stripe and the polyphyly of other leaf-stripe smuts within Ustilago. Furthermore, smut specimens from the same host genus generally clustered together in well-supported clades that often had available species names for these lineages. In addition to already-named lineages, three new lineages were observed, and described as new species on the basis of host specificity and molecular differences: namely Ustilago jagei sp. nov. on Agrostis stolonifera, U. kummeri sp. nov. on Bromus inermis, and U. neocopinata sp. nov. on Dactylis glomerata.

Keywords: DNA-based taxonomy; Ustilaginaceae; host specificity; molecular species discrimination; multigene phylogeny; new taxa; species complex.

Fig. 1.

Phylogenetic tree based on Minimum Evolution analysis of nine loci (ITS, myosin, map, rpl3, tif2, ssc1, sdh1, rpl4A, atp2). Numbers on branches denote support in Minimum Evolution, Maximum Likelihood and Bayesian Analyses, in the respective order. Values below 55 % are denoted by ‘-‘. The bar indicates the number of substitutions per site.

Fig. 2.

Phylogenetic tree based on Minimum Evolution analysis of three loci (ITS, ssc1, atp2). Numbers on branches denote support in Minimum Evolution, Maximum Likelihood and Bayesian Analyses, in the respective order. Values below 55 % are denoted by ‘-‘.. The bar indicates the number of substitutions per site.

Fig. 3.

Phylogenetic tree based on Minimum Evolution analysis of nine loci (ITS, myosin, map, rpl3, tif2, ssc1, sdh1, rpl4A, atp2) detailed showing the Ustilago striiformis-complex with the outgroup U. cynodontis. Numbers on branches denote support in Minimum Evolution, Maximum Likelihood and Bayesian Analyses, in the respective order. Values below 55 % are denoted by ‘-‘. The bar indicates the number of substitutions per site.

Fig. 4.

Phylogenetic tree based on Minimum Evolution analysis of three loci (ITS, ssc1, atp2) detailed showing the Ustilago striiformis-complex with the outgroup U. cynodontis. Numbers on branches denote support in Minimum Evolution, Maximum Likelihood and Bayesian Analyses, in the respective order. Values below 55 % are denoted by ‘-‘. The bar indicates the number of substitutions per site.

Fig. 5.

Sori and spores of Ustilago jagei (A–B), U. denotarisii (C–D), U. neocopinata (E–F), U. salweyi (G–H), U. kummeri (I–J), and U. serpens s. str. (K–L). A. Sori of U. jagei on Agrostis stolonifera (GLM-F047379); B. Teliospores seen by LM; C. Sori of U. denotarisii on Arrhenatherum elatius (GLM-F105836); D. Teliospores seen by LM; E. Sori of U. neocopinata on Dactylis glomerata (GLM-F107413); F. Teliospores seen by LM; G. Sori of U. salweyi on Holcus lanatus (GLM-F107417); H. Teliospores seen by LM; I. Sori of U. kummeri on Bromus inermis (GLM-F107435); J. Teliospores seen by LM; K. Sori of U. serpens s. str. on Elymus repens (GLM-F105827); and L. Teliospores seen by LM.

Fig. 6.

Alignment consensus sequences for the alignments used in this study with positions of diagnostic bases highlighted in bold face.