Deciphering Species Complexes: Puccinia Andropogonis and Puccinia Coronata, Examples of Differing Modes of Speciation
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Mycoscience (2006) 47:130–136 © The Mycological Society of Japan and Springer-Verlag Tokyo 2006 DOI 10.1007/s10267-006-0287-7 FULL PAPER Les J. Szabo Deciphering species complexes: Puccinia andropogonis and Puccinia coronata, examples of differing modes of speciation Received: November 30, 2005 / Accepted: January 20, 2006 Abstract Species of macrocyclic, heteroecious grass rusts problematic. Five spores stages may be produced in the life often have been defined with wide host ranges and variation cycle of macrocyclic heteroecious grass rust, but relatively in spore morphology. Consequently, some are species com- few morphological characters usually delineate species on a plexes and contain genetically distinct forms. Molecular given family of hosts (Baum and Savile 1985). Identifying analyses, together with morphological and biological meth- host range on telial and aecial hosts is difficult, and in many ods, provide powerful means to dissect these complexes. cases the aecial hosts are unknown. For rusts of cereals and Puccinia coronata is a complex species that has a broad grasses, this has resulted in broadly defined species. Many telial host range including more than 45 genera of grasses are described as having a large number of telial and/or and a narrow aecial host range. Phylogenetic analysis of aceial hosts, and species descriptions may include rather nuclear ribosomal internal transcribed spacer (ITS) DNA broad morphological variation (Arthur 1934; Cummins sequences from 15 aecial and telial collections grouped 1971). P. coronata into six distinct clades supporting separa- Puccinia coronata Corda is widely distributed around the tion of this complex into four distinct species. Puccinia globe and is the causal agent of crown rust, an economically andropogonis, a common rust of tall prairie grasses in North important disease on cereal and grass hosts. The common America, is also a complex species. However, in contrast to name, crown rust, is derived from the crown-like append- P. coronata, P. andropogonis has a narrow telial host range ages on the apex of the teliospore. Puccinia coronata has a and a broad aecial host range. DNA sequence analysis broad telial host range, including more than 45 genera of grouped 15 collections of P. andropogonis into six distinct grasses, and a relatively narrow aecial host range, prim- clades representing at least four distinct species. Speciation arily on species of Rhamnus (Rhamnaceae) but also of of P. coronata appears to have occurred primarily by radia- Berchemia (Rhamnaceae) and Elaeagnus (Elaeagnaceae) tion onto new telial hosts, whereas in P. andropogonis spe- (Cummins 1971; Urban and Marková 1994). Puccinia ciation appears to have occurred primarily by radiation coronata has been subdivided into formae speciales based onto new aecial hosts. on telia host range (Eriksson and Henning 1894; Eriksson 1908; Brown 1937; Peturson 1954), leading to 13 subgroups. Key words Evolution · ITS · Phylogenetics · Species com- P. coronata f. sp. avenae on Avena sativa (oat) is the most plex · Uredinales economically important. However, overlap in host range among formae speciales has led to confusion (Eshed and Dinoor 1981). Others have used both morphological char- Introduction acters and host range to subdivide P. coronata into varieties; Cummins (1971) recognized five and Urban and Marková (1994) recognized four. Phylogenetic relationships within and among rust species In contrast to P. coronata, the grass rust, P. andropogonis have historically been inferred based on range of host spe- Schw., has a relatively narrow telial host range and broad cies and spore morphology; however, both approaches are aecial host range. Telial hosts of P. andro-pogonis include Andropogon gerardii (big bluestem) and Schizachyrium scoparis (little bluestem), primary grass species in North L.J. Szabo (*) American tall-grass prairies. Aecial hosts are found in Cereal Disease Laboratory, USDA Agricultural Research Service, seven diverse host families (Fabaceae, Hippocostanaceae, Department of Plant Pathology, University of Minnesota, 1551 Oxalidaceae, Polygalaceae, Rutaceae, Santalaceae, and Lindig Street, St. Paul, MN, USA Tel. +1-612-625-3780; Fax +1-651-649-5055 Scrophulariacea) in a total of 17 host genera (Arthur 1934; e-mail: [email protected] Cummins 1971). A common characteristic of the tall-grass 131 Table 1. Rust collections used in this study Rust, host Collectionsa Location GenBank accession no. Puccinia andropogonis Telial host Andropogon gerardii HSZ0027 USA, Wisconsin, Fish Lake DQ344518 HSZ0219 USA, Wisconsin, Fish Lake DQ344517 HSZ0224 USA, Minnesota, CCNHA DQ344512 HSZ0237 USA, Minnesota, CCNHA DQ344511 HSZ0574 USA, Wisconsin, Fish Lake DQ344515 HSZ0576 USA, Wisconsin, Fish Lake DQ344514 Schizachyrium scoparis HSZ0217 USA, Wisconsin, Grantsburg DQ344507 HSZ0225 USA, Minnesota, Afton DQ344505 HSZ0562 USA, Minnesota, Afton DQ344510 Aecial host Castilleja coccinea HSZ0388 USA, Minnesota, Afton DQ344509 HSZ0389 USA, Minnesota, Afton DQ344508 Comandra umbellata HSZ0263 USA, Wisconsin, Fish Lake DQ344513 Lupinus perennis HSZ0264 USA, Wisconsin, Fish Lake DQ344519 Penstemon gracilis HSZ0262 USA, Wisconsin, Fish Lake DQ344506 Zanthoxylum americanum HSZ0265 USA, Wisconsin, Fish Lake DQ344516 Puccinia coronata Telial host Arrhenatherum elatius PRC 190 Czech Republic, Bohemia DQ355443 Avena sativa CDL 93MN437 USA, Minnesota AY114290 Bromus erectus PRC 194 Slovakia DQ355449 PRC 196 Czech Republic, Bohemia DQ355450 B. inermis HSZ1400 USA DQ355448 HSZ1401 USA DQ355446 Calamagrostis canadensis CDL 91WI9526 USA, Wisconsin L08694b Elytrigia repens CDL 73MN873 USA, Minnesota DQ414723 CDL MN01 USA, Minnesota DQ414724 Holcus lanatus PRC 200 Ireland DQ355444 Lolium perenne PRC 203 Czech Republic, Bohemia DQ355441 Aecial host Rhamnus catharticus HSZ0757 USA, Minnesota DQ355445 HSZ0760 USA, Minnesota DQ355447 HSZ0761 USA, Minnesota DQ355442 HSZ1309 USA, New York DQ355452 R. saxatilis PRC 247 Slovakia DQ355451 a Prefix designations and sources for collections: CDL, USDA ARS Cereal Disease Laboratory; HSZ, L.J. Szabo; PRC, J. Marková, Charles University, Prague, Czech Republic b Zambino and Szabo (1993) prairie is the rich diversity of plant species where several Materials and methods telial and aecial hosts are often found in close proximity. Arthur (1934) subdivided P. andropogonis into nine variet- Collections ies based primarily on aecial hosts but also on the number and placement of uredi-niospore germ pores. More recently, The rust collections used in this study, their hosts, and their Cummins (1953) proposed four variants of P. andropogonis geographical origins are listed in Table 1. Fifteen samples of based on urediniospore morphology. Puccinia andropogonis were collected from the northern DNA sequence analysis of nuclear ribosomal internal plains of the United States (Minnesota and Wisconsin) in transcribed spacer (ITS) region has been used to resolve sites representing both disturbed sites and natural habitats. phylogenetic relationships among closely related rust fungi Fifteen samples of P. coronata were collected from central (Zambino and Szabo 1993; Pfunder et al. 2001; Vogler and United States and Europe in sites representing cultivated Bruns 1998; Weber et al. 2003). Phylogenetic analysis of fields, disturbed sites, and natural habitats. the P. coronata complex (based on partial ITS sequence data) resulted in three distinct groups: Calamagrostis type, Avena/Lolium type, and Elytrigia repens (=Agropyron Polymerase chain reaction and DNA sequencing repens) type (Zambino and Szabo 1993). To expand on this study, the complete ITS region was cloned and sequenced DNA was extracted from either dried urediniospores col- from representatives of two of these three groups as well as lected from infected host material or from dried infected from additional collections of P. coronata. A parallel study host leaf tissue as described by Anikster et al. (2004). In was carried out on collections of the P. andropogonis some cases, an OminiPrep (Genotech, St. Louis, MO, USA) complex. DNA extraction kit was used instead of the CTAB DNA 132 Fig. 1. Parsimony tree from the analysis of nuclear ribosomal internal transcribed spacer (ITS) region sequence data of Puccinia coronata. Phylogenetic analysis resulted in three optimal trees, each with a tree length of 185 steps (CI = 0.9081, HI = 0.0919, RI = 0.9424, and RC = 0.8518), one of which is shown. Numbers above or below branches indicate percentage of congruent clusters in 1000 bootstrap trials, and only values above 80% are shown. Clades are indicated along the right-hand side. Two DNA sequences of P. graminis (AY114289, DQ355455) were used as an outgroup extraction method. Nuclear ribosomal internal transcribed providing an aligned sequence of 1308 characters. Variation spacer (ITS) region and the 5′-end of the large subunit were in the 5′-end of the 28S was low and therefore not included amplified using polymerase chain reaction (PCR), and in the phylogenetic analysis. Of the 649 aligned characters amplification products were cloned (Anikster et al. 2004). analyzed, 508 were constant, 34 were variable but uninfor- Primer pairs used for amplification were ITS1F (Gardes mative, and 107 characters were parsimony-informative. and Bruns 1993) and RUST1 (Kroop et al. 1995). DNA Parsimony analysis of ITS sequence data from 15 collec- sequencing reactions were performed using a Thermo tions resulted in three optimal trees, each with a tree length Sequenase Primer Cycle sequencing kit (GE