Take-All Disease: New Insights into an Important Wheat Root Pathogen

Take-all disease, caused by the fungal root pathogen Gaeumannomyces tritici, is considered to be the most important root disease of wheat worldwide. Here we review the advances in take-all research over the last 15 years, focusing on the identification of new sources of genetic resistance in wheat relatives and the role of the microbiome in disease development. We also highlight recent breakthroughs in the molecular interactions between G. tritici and wheat, including genome and transcriptome analyses. These new findings will aid the development of novel control strategies against take-all disease. In light of this growing understanding, the G. tritici-wheat interaction could provide a model study system for root-infecting fungal pathogens of cereals.

Gaeumannomyces nanograminis, sp. nov., a hyphopodiate fungus identified from diseased roots of ultradwarf bermudagrass in the United States

The genus Gaeumannomyces (Magnaporthaceae, Magnaporthales, Sordariomycetes, Ascomycota) includes root-infecting pathogens, saprobes, and endophytes. Morphological, biological, and phylogenetic analyses were employed to identify fungal isolates derived from turfgrass roots colonized with ectotrophic, dark runner hyphae. Phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes were obtained via maximum likelihood and Bayesian methods. Our isolates consistently formed a distinct and highly supported clade within Gaeumannomyces. Common and distinctive biological and morphological characters reinforced these findings. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey), its native host, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Gaeumannomyces nanograminis, associated with rotted roots of ultradwarf bermudagrass.

Magnaporthiopsis cynodontis, a novel turfgrass pathogen with widespread distribution in the United States

The genus Magnaporthiopsis of Magnaporthaceae (Magnaporthales, Sordariomycetes, Ascomycota) contains species that are predominantly necrotrophic pathogens, often producing simple hyphopodia and dark, ectotrophic runner hyphae on plant roots and stems during colonization. Fungal isolates from turfgrass roots with dark and ectotrophic runner hyphae were examined and identified based on morphological, biological, and phylogenetic analyses. Maximum likelihood and Bayesian methods were implemented to obtain phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions, and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes. Our isolates consistently formed a distinct and highly supported clade within Magnaporthiopsis. These findings were reinforced by common and distinctive biological and morphological characters. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass, one of its native hosts, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Magnaporthiopsis cynodontis, which has widespread distribution in the United States.

Fungal Systematics and Evolution: FUSE 5

Thirteen new species are formally described: Cortinarius brunneocarpus from Pakistan, C. lilacinoarmillatus from India, Curvularia khuzestanica on Atriplex lentiformis from Iran, Gloeocantharellus neoechinosporus from China, Laboulbenia bernaliana on species of Apenes, Apristus, and Philophuga (Coleoptera, Carabidae) from Nicaragua and Panama, L. oioveliicola on Oiovelia machadoi (Hemiptera, Veliidae) from Brazil, L. termiticola on Macrotermes subhyalinus (Blattodea, Termitidae) from the DR Congo, Pluteus cutefractus from Slovenia, Rhizoglomus variabile from Peru, Russula phloginea from China, Stagonosporopsis flacciduvarum on Vitis vinifera from Italy, Strobilomyces huangshanensis from China, Uromyces klotzschianus on Rumex dentatus subsp. klotzschianus from Pakistan. The following new records are reported: Alternaria calendulae on Calendula officinalis from India; A. tenuissima on apple and quince fruits from Iran; Candelariella oleaginescens from Turkey; Didymella americana and D. calidophila on Vitis vinifera from Italy; Lasiodiplodia theobromae causing tip blight of Dianella tasmanica 'variegata' from India; Marasmiellus subpruinosus from Madeira, Portugal, new for Macaronesia and Africa; Mycena albidolilacea, M. tenuispinosa, and M. xantholeuca from Russia; Neonectria neomacrospora on Madhuca longifolia from India; Nothophoma quercina on Vitis vinifera from Italy; Plagiosphaera immersa on Urtica dioica from Austria; Rinodina sicula from Turkey; Sphaerosporium lignatile from Wisconsin, USA; and Verrucaria murina from Turkey. Multi-locus analysis of ITS, LSU, rpb1, tef1 sequences revealed that P. immersa, commonly classified within Gnomoniaceae (Diaporthales) or as Sordariomycetes incertae sedis, belongs to Magnaporthaceae (Magnaporthales). Analysis of a six-locus Ascomycota-wide dataset including SSU and LSU sequences of S. lignatile revealed that this species, currently in Ascomycota incertae sedis, belongs to Pyronemataceae (Pezizomycetes, Pezizales).

Magnaporthiopsis meyeri-festucae, sp. nov., associated with a summer patch-like disease of fine fescue turfgrasses

Summer patch is a common and destructive root disease of turfgrasses. In this study, a new Magnaporthiopsis species, M. meyeri-festucae, was identified from the roots of fine fescue (Festuca spp.) turfgrasses with summer patch-like symptoms. It is described and illustrated on the basis of phenotypic characteristics and partial sequences of rDNA 18S, internal transcribed spacer (ITS), and 28S regions, and of MCM7, RPB1, and TEF1 genes. A key for all seven described species in the genus Magnaporthiopsis is provided. Distinctions between the new species and related species are discussed. Fulfillment of Koch's postulates confirmed Magnaporthiopsis meyeri-festucae as a pathogen causing summer patch-like symptoms of fine fescue turfgrasses. This work is the basis for future studies on biogeography, host range, and impact of summer patch pathogens on a broader scale.

Take-all or nothing

Take-all disease of Poaceae is caused by Gaeumannomyces graminis (Magnaporthaceae). Four varieties are recognised in G. graminis based on ascospore size, hyphopodial morphology and host preference. The aim of the present study was to clarify boundaries among species and varieties in Gaeumannomyces by combining morphology and multi-locus phylogenetic analyses based on partial gene sequences of ITS, LSU, tef1 and rpb1. Two new genera, Falciphoriella and Gaeumannomycella were subsequently introduced in Magnaporthaceae. The resulting phylogeny revealed several cryptic species previously overlooked within Gaeumannomyces. Isolates of Gaeumannomyces were distributed in four main clades, from which 19 species could be delimited, 12 of which were new to science. Our results show that the former varieties Gaeumannomyces graminis var. avenae and Gaeumannomyces graminis var. tritici represent species phylogenetically distinct from G. graminis, for which the new combinations G. avenae and G. tritici are introduced. Based on molecular data, morphology and host preferences, Gaeumannomyces graminis var. maydis is proposed as a synonym of G. radicicola. Furthermore, an epitype for Gaeumannomyces graminis var. avenae was designated to help stabilise the application of that name.

Resolving the polyphyletic nature of Pyricularia (Pyriculariaceae)

Species of Pyricularia (magnaporthe-like sexual morphs) are responsible for major diseases on grasses. Pyricularia oryzae (sexual morph Magnaporthe oryzae) is responsible for the major disease of rice called rice blast disease, and foliar diseases of wheat and millet, while Pyricularia grisea (sexual morph Magnaporthe grisea) is responsible for foliar diseases of Digitaria. Magnaporthe salvinii, M. poae and M. rhizophila produce asexual spores that differ from those of Pyricularia sensu stricto that has pyriform, 2-septate conidia produced on conidiophores with sympodial proliferation. Magnaporthe salvinii was recently allocated to Nakataea, while M. poae and M. rhizophila were placed in Magnaporthiopsis. To clarify the taxonomic relationships among species that are magnaporthe- or pyricularia-like in morphology, we analysed phylogenetic relationships among isolates representing a wide range of host plants by using partial DNA sequences of multiple genes such as LSU, ITS, RPB1, actin and calmodulin. Species of Pyricularia s. str. belong to a monophyletic clade that includes all P. oryzae/P. grisea isolates tested, defining the Pyriculariaceae, which is sister to the Ophioceraceae, representing two novel families. These clades are clearly distinct from species belonging to the Gaeumannomyces pro parte/Magnaporthiopsis/Nakataea generic complex that are monophyletic and define the Magnaporthaceae. A few magnaporthe- and pyricularia-like species are unrelated to Magnaporthaceae and Pyriculariaceae. Pyricularia oryzae/P. grisea isolates cluster into two related clades. Host plants such as Eleusine, Oryza, Setaria or Triticum were exclusively infected by isolates from P. oryzae, while some host plant such as Cenchrus, Echinochloa, Lolium, Pennisetum or Zingiber were infected by different Pyricularia species. This demonstrates that host range cannot be used as taxonomic criterion without extensive pathotyping. Our results also show that the typical pyriform, 2-septate conidium morphology of P. grisea/P. oryzae is restricted to Pyricularia and Neopyricularia, while most other genera have obclavate to more ellipsoid 2-septate conidia. Some related genera (Deightoniella, Macgarvieomyces) have evolved 1-septate conidia. Therefore, conidium morphology cannot be used as taxonomic criterion at generic level without phylogenetic data. We also identified 10 novel genera, and seven novel species. A re-evaluation of generic and species concepts within Pyriculariaceae is presented, and novelties are proposed based on morphological and phylogenetic data.