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Two New Species of Rhynchosporium

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Two New Species of Rhynchosporium Mycologia, 103(1), 2011, pp. 195–202. DOI: 10.3852/10-119 # 2011 by The Mycological Society of America, Lawrence, KS 66044-8897 Two new species of Rhynchosporium Pascal L. Zaffarano from the Netherlands by Oudemans (Oudemans Forest Pathology and Dendrology, Institute of Integrative 1897). In the same year another description was Biology (IBZ), ETH Zu¨ rich, 8092 Zu¨ rich, Switzerland made in Germany and the fungus was named Bruce A. McDonald Rhynchosporium graminicola (Frank 1897). Later both Plant Pathology, Institute of Integrative Biology (IBZ), Davis (1919, 1921) and Caldwell (1937) proposed the ETH Zu¨ rich, 8092 Zu¨ rich, Switzerland combination of the two names that led to today’s generally accepted name of R. secalis. It is likely that 1 Celeste C. Linde R. secalis is a member of the Helotiales because Evolution, Ecology and Genetics, Research School of comparisons of ITS and mating-type DNA sequences Biology, College of Medicine, Biology and Environment, Building 116, Daley Road, Australian National showed that the species is closely related to the University, Canberra, ACT 0200, Australia helotialean plant pathogens Pyrenopeziza brassicae and Oculimacula yallundae (Goodwin 2002, Foster and Fitt 2004). The only other known Rhynchosporium Abstract: Rhynchosporium consists of two species, R. species is R. orthosporum,isolatedfromDactylis secalis and R. orthosporum. Both are pathogens of glomerata (Caldwell 1937). Rhynchosporium orthos- grasses with R. secalis infecting a variety of Poaceae porum is morphologically different from R. secalis hosts and R. orthosporum infecting Dactylis glomerata. because it lacks the typical beaked form of the Phylogenetic analyses of multilocus DNA sequence conidia. data on R. secalis isolates originating from cultivated In Zaffarano et al. (2006) we detected significant barley, rye, triticale and other grasses, including population genetic evidence for host specialization Agropyron spp., Bromus diandrus and Hordeum spp., with RFLP markers. A population originating from a resolved the monophyletic groups into three species Swiss rye field was genetically differentiated (GST 5 according to their respective hosts. Host specificity 0.59) when compared to 30 barley-infecting popula- according to phylogenetic lineages was confirmed tions from different continents (Zaffarano et al. with pathogenicity studies. Because R. secalis was 2006). Findings of high population subdivision and described first on rye this name is retained for a low number of shared alleles between barley- and Rhynchosporium isolates infecting rye and triticale. rye-infecting populations, as well as an abundance of Rhynchosporium isolates infecting cultivated barley private alleles in the rye-infecting population, were and other Hordeum spp. and Bromus diandrus belong interpreted as evidence for genetic isolation between to a distinct species, R. commune. Similarly isolates the host populations despite the geographical prox- infecting Agropyron spp. represent a distinct species of imity of the two hosts in Switzerland (Zaffarano et al. Rhynchosporium, namely R. agropyri. A PCR-RFLP 2006). Later work with multilocus sequence analyses assay was developed as a rapid tool for species further suggested that rye/triticale-infecting as well as identification of R. secalis and R. commune. Agropyron-infecting populations represented species Key words: agriculture, cereal crops, Helotiales, distinct from R. secalis, which likely originated by host specialization, infectious diseases, speciation genetic divergence due to host specialization (Zaffar- ano et al. 2008, 2009). This idea was corroborated by a microsatellite study showing that 13 of the 14 loci INTRODUCTION developed with a barley-infecting strain of Rhynchos- Two reported species of the fungal anamorph genus porium could be amplified in Rhynchosporium popu- Rhynchosporium infect cereals and grasses. Rhynchos- lations infecting rye, whereas only nine of the 14 loci porium secalis (Oudem.) J.J. Davis causes the necrotic could be amplified in Agropyron-infecting populations disease called scald or leaf blotch on barley, rye, (C.C. Linde unpubl). Finally host specialization of triticale and other Poaceae, especially on species of rye-, barley- and Agropyron-infecting Rhynchosporium Hordeum, Agropyron, Bromus and Lolium (Caldwell isolates was demonstrated by cross-infection studies 1937, Shipton et al. 1974, Welty and Metzger 1996). (Zaffarano et al. 2008). Together these findings The first descriptions and designation of the organ- suggested that R. secalis is composed of three cryptic ism (Marsonia secalis) isolated from rye dates to 1897 species. Here we propose that more than two species of Submitted 21 Apr 2010; accepted for publication 19 Jul 2010. Rhynchosporium, specialized on different hosts, can be 1 Corresponding author. E-mail: [email protected] distinguished. We summarize previously published 195 196 MYCOLOGIA evidence from studies based on pathogenicity, popu- product. The reaction was incubated at 30 C in a lation genetics and multilocus phylogenetic analyses. thermocycler 1 h and chilled on ice. Fragments were Species descriptions of two new species of Rhynchos- separated on a 1.5% agarose gel containing ethidium porium are provided. bromide and viewed on a UV transilluminator. MATERIALS AND METHODS RESULTS Fungal isolates and molecular analyses.—Sequence data Phylogenetic analyses.—DNA sequences of a-tubulin, comprised the sequences of isolates from hosts used in b-tubulin and ITS obtained from 316 Rhynchosporium our earlier phylogenetic studies and included eight loci: the isolates were concatenated and collapsed into 45 four housekeeping genes ITS, translation elongation factor haplotypes (H1–H45) to construct a Bayesian maxi- 1 alpha (EF-1a), a-tubulin and b-tubulin, as reported in mum likelihood tree. The multilocus phylogenetic Zaffarano et al. (2008), as well as the two non-coding analyses (FIG. 1) resulted in Rhynchosporium secalis nuclear RFLP loci, pRS6 and pRS52, and parts of the being divided into three host-associated clades with MAT1-1 and MAT1-2 idiomorphs of the mating-type locus strong Bayesian posterior probability support (FIG. 1). (Zaffarano et al. 2009). The total number of isolates The first clade of R. secalis consisted of haplotypes from different hosts was Rhynchosporium isolates infecting from barley and other Hordeum species as well as cultivated barley (n 5 586), Hordeum leporinum (n 5 37), Hordeum murinum (n 5 9), Hordeum spontaneum (n 5 12), Bromus diandrus and hereafter will be referred to as Bromus diandrus (n 5 2), rye (n 5 76), triticale (n 5 28), Rhynchosporium commune Zaffarano, McDonald and Agropyron repens (n 5 66), Agropyron caninum (n 5 1) and Linde sp. nov. The second clade consisted of R. secalis Dactylis glomerata (n 5 13). These isolates originated from from rye and triticale, and the third clade consisted of more than 65 sites on five continents. Detailed descriptions haplotypes from two Agropyron species, hereafter of isolate origins, DNA extraction and sequencing methods referred to as Rhynchosporium agropyri Zaffarano, were provided by Zaffarano et al. (2008, 2009). McDonald and Linde sp. nov. All three sequence loci The number of polymorphisms that were fixed between could distinguish among R. secalis, R. commune and host-infecting populations was calculated for all eight R. agropyri. The total number of fixed sequence sequence loci with the program DnaSP 4.0 (Rozas et al. differences between these species was 0.75–1.39% 2003). A Bayesian maximum likelihood tree was constructed based on the eight sequence loci (TABLE I). in MrBayes 3.0b4 (Ronquist and Huelsenbeck 2003) based on a three-gene dataset (a-tubulin and b-tubulin, ITS; PCR-RFLP.—The PCR-RFLP assay could differentiate 3066 bp total concatenated sequence length) to represent isolates associated with rye and triticale from all other evolutionary relationships among Rhynchosporium strains isolates tested associated with barley (FIG. 2). The C-T isolated from hosts. For this analysis identical DNA sequences transition at position 332 in the ITS region resulted in were assigned to haplotypes and redundant sequences removed. Details of the analysis are given in Zaffarano et al. the absence of a SmaI restriction site in isolates from (2008), and GenBank accession numbers are HM627410– barley, Hordeum spp., Bromus diandrus and Agropyron HM627427 for a-tubulin, HM627428–HM627452 for b- spp. A subsample of 22 isolates was used to evaluate tubulin and HM627468–HM627492 for ITS. the assay. The two predicted PCR-RFLP phenotypes could be distinguished on an agarose gel (FIG. 2), RFLP-PCR screening for species identification.—A RFLP-PCR indicating that this assay provides a simple and rapid method for differentiating species was developed based on the ITS locus. A subsample of 22 isolates representing diagnostic tool to distinguish between the barley- and groups infecting barley, rye and triticale was used to rye/triticale-infecting species. evaluate this assay. Isolation and culturing of fungal isolates as well as DNA extraction were as described in McDonald et TAXONOMY al. (1999) and Zaffarano et al. (2008). ITS regions were amplified with PCR primers ITS4 and ITS5 (White et al. Rhynchosporium commune Zaffarano, McDonald 1990). PCR reactions were carried out in 20 mL volumes and Linde sp. nov. FIG.1 containing 2 mL103 PCR buffer, 0.1 mM each dNTP, 0.5 mM 5 Rhynchosporium secalis sensu Oudemans (1897), each primer, 0.5 U Taq polymerase (New England BioLabs,
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