Stripe smuts of grasses: one lineage or high levels of polyphyly?

Abstract

Stripe smut of grasses, Ustilago striiformis s.l., is a complex of smut fungi widely distributed over temperate and subtropical regions. The disease results in the shredding and death of leaf tissue following the rupture of elongated sori. Nearly 100 different grass species in more than 30 genera are infected by stripe smut. During the last two centuries more than 30 smut taxa have been described from members of this complex. The present study attempts to clarify the taxonomy and phylogeny of stripe smuts on grasses by analysing both morphological and molecular data. More than 200 specimens from different continents and host plants were examined. DNA was extracted from teliospores of 23 specimens from different hosts collected in Europe, Asia, and North America. The ITS and LSU regions of ribosomal DNA were amplified and used in phylogenetic analyses. The results of Maximum Parsimony and Bayesian analyses demonstrated that there are several lineages of stripe smut fungi. Analyses of morphological characters assessed with light and scanning electron microscopy showed high support for the differentiation of two clades as distinct from U. striiformis s.l., i.e., U. nunavutica sp. nov. and U. bromina. Two additional clades, U. striiformis s.str. on Holcus and a clade containing specimens from Elymus, were identified with molecular data although morphological differences were not apparent. Descriptions are given for each species.

Ustilago species causing leaf-stripe smut revisited

“…Of these species, U. striiformis s. lat ., with the type species described on Holcus lanatus , is a complex occurring on 164 species of Poaceae representing 44 different genera ( Achnatherum , Agropyron , Agrostis , Alopecurus , Ammophila, Anthoxanthum, Arctagrostis, Arrhenatherum, Avena, Beckmannia, Brachypodium , Briza , Bromus , Calamagrostis , Cleistogenes , Cynosurus , Dactylis , Danthonia , Deschampsia , Deyeuxia , Elymus , Festuca , Helictotrichon , Hierochloë , Holcus , Hordeum , Hystrix , Koeleria , Leymus , Lolium , Melica , Milium , Pennisetum , Phalaris , Phleum , Piptatherum , Poa , Polypogon , Puccinellia , Sesleria , Setaria , Sitanion , Trisetaria , and Trisetum ). Based on host specificity and minor differences in spore size and surface ornamentation, approximately 30 different taxa have been described in the U. striiformis species complex on various host plants ( Vánky 2012 , Savchenko et al 2014a ). Ustilago serpens probably represents an overlooked species complex, occuring on five host genera: Agropyron , Brachypodium , Bromus , Elymus , and Leymus .…”

“…The morphological difference was mainly in spore size and ornamentation. Savchenko et al (2014a) provided a more detailed analysis of the U. striifomis species complex using several host-fungus combinations and phylogenetic reconstructions based on the nrITS and partial LSU regions. However, while two additional species were proposed as distinct in the U. striiformis -complex, the phylogenetic resolution was too low to draw further conclusions regarding host specificity and potential species boundaries.…”

What causes flag smut of wheat?

“…The results of the phylogenetic analysis further indicates that species of Urocystis on triticoid hosts have narrow host ranges. These results coincide with similar studies on other groups of smut fungi, supporting the hypothesis that most smut fungi are restricted to a single genus or, sometimes, to a single species of plant (Vánky & Lutz, , ; Bauer et al ., ; Lutz et al ., , ,b; Kemler et al ., ; Piątek et al ., , , ,b; Savchenko et al ., , ,b, ). These findings may affect regulatory policy, as they indicate that flag smuts on other hosts are unlikely to spread to wheat.…”

“…Until recently, molecular studies in plant pathogenic smut fungi have relied primarily on the LSU and internal transcribed spacer (ITS) regions of the nuclear rDNA to estimate evolutionary relationships (V anky & Lutz, 2007(V anky & Lutz, , 2010Bauer et al, 2008;Lutz et al, 2008Lutz et al, , 2012aKemler et al, 2009;Pia z tek et al, 2011Pia z tek et al, , 2012Pia z tek et al, , 2013aPia z tek et al, , b, 2015aSavchenko et al, 2014a). Fewer studies have incorporated additional gene regions, such as the TEF (Carris et al, 2007;Munkacsi et al, 2007;Bao et al, 2010;McTaggart et al, 2012), GAPDH (Munkacsi et al, 2007;McTaggart et al, 2012), ATP6 (Munkacsi et al, 2007), COX3 (Munkacsi et al, 2007) and RPB1 (Munkacsi et al, 2007).…”

A molecular phylogenetic framework for Anthracocystis (Ustilaginales), including five new combinations (inter alia for the asexual Pseudozyma flocculosa), and description of Anthracocystis grodzinskae sp. nov.

“…For further resolution of relationships between Anthracocystis species, other genes should be analysed, but for routine species identification and generic placement, the current concatenated ITS+LSU dataset suits well. Thus, similar to resolved backbone trees for different phytopathogenic fungi (e.g., Begerow et al 2002;Hendrichs et al 2005;Lutz et al 2005Lutz et al , 2008Maharachchikumbura et al 2012;Piątek et al 2013;Hyde et al 2014;Savchenko et al 2014;Ariyawansa et al 2015;McTaggart et al 2015), the concatenated dataset (alignment deposited in TreeBASE S17942) is intended to serve as a phylogenetic backbone for the genus Anthracocystis for future molecular studies. In addition to currently accepted Anthracocystis species, this study determined that another species, Sporisorium andrewmitchellii , was nested within Anthracocystis.…”