Pyricularia
Sacc. Michelia 2: 20. 1880. Fig. 52.
Fig. 52. Pyricularia spp. A–C. Leaf spots of rice caused by Pyricularia oryzae. D–H. Sexual morph of Pyricularia oryzae. D, E. Crossing of different strains of Pyricularia oryzae to produce the sexual morph. F. Ascoma. G. Asci. H. Germinating ascospore. I–U. Asexual morph. I, J. Sporulation on sterile barley seed on SNA. I. Pyricularia grisea (BR0029). J. Pyricularia graminis-tritici (ex-type URM7380). K–P. Conidiophores and conidia. K, L. Pyricularia ctenantheicola (GR0002). M, N. Pyricularia graminis-tritici (ex-type URM7380). O. Pyricularia oryzae (URM7369). P. Pyricularia oryzae (BF0028). Q–S. Conidia. Q. Pyricularia ctenantheicola (GR0002). R. Pyricularia oryzae (URM7369). S. Pyricularia graminis-tritici (ex-type URM7380). T. Macroconidia of Pyricularia grisea (BR0029) (arrows indicate apical marginal frill, which is a remnant of the apical mucoid cap). U. Microconidia of Pyricularia grisea (BR0029). Scale bars: F = 50 μm; others = 10 μm. Pictures D, E, G taken by Dounia Saleh, CIRAD; F, H by Didier Tharreau, CIRAD; I, K, L, P, Q, T from Klaubauf et al. (2014); J, M–O, R, S from Castroagudín et al. (2016).
Classification: Sordariomycetes, Sordariomycetidae, Magnaporthales, Pyriculariaceae.
Type species: Pyricularia grisea Sacc. Lectotype designated by Rossman et al. (1990): BPI undistributed set. Epitype and ex-epitype strain designated by Crous et al. (2015a): CBS H-22280, CBS 138707.
DNA barcode (genus): LSU.
DNA barcodes (species): ITS, act, cal, rpb1. Table 18. Fig. 28.
Table 18. DNA barcodes of accepted Pyricularia spp.
| Species | Isolates1 | GenBank accession numbers2 | References | |||
|---|---|---|---|---|---|---|
| ITS | act | cal | rpb1 | |||
| Pyricularia angulata | NBRC 9625 | AY265322 | – | – | – | Bussaban et al. (2005) |
| Py. ctenantheicola | CBS 138601T | KM484879 | KM485183 | KM485253 | KM485099 | Klaubauf et al. (2014) |
| Py. graminis-tritici | URM7380T | – | KU952138 | KU952892 | – | Castroagudín et al. (2016) |
| Py. grisea | CBS 128304 | KM484881 | KM485184 | KM485255 | KM485101 | Klaubauf et al. (2014) |
| Py. oryzae | CBS 255.38 | KM484889 | KM485190 | KM485261 | KM485109 | Klaubauf et al. (2014) |
| Py. penniseticola | CBS 138603T | KM484929 | KM485220 | – | KM485148 | Klaubauf et al. (2014) |
| Py. pennisetigena | CBS 138604T | KM484935 | KM485225 | KM485294 | KM485153 | Klaubauf et al. (2014) |
| Py. urashimae | CBS 142117T | KY173437 | KY173571 | – | KY173578 | Crous et al. (2016a) |
| Py. zingibericola | CBS 138605T | KM484941 | KM485229 | KM485297 | KM485157 | Klaubauf et al. (2014) |
- 1
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CBS: Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands; NBRC: Biological Resource Center, NITE, Chiva, Japan; URM: Culture Collection Mycobank, Prof. Maria Auxiliadora Cavalcanti, Federal University of Pernambuco, Recife, Brazil. T indicates ex-type strains.
- 2
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ITS: internal transcribed spacers and intervening 5.8S nrDNA; act: partial actin gene; cal: partial calmodulin gene; rpb1: partial RNA polymerase II largest subunit gene.
Ascomata ostiolate, solitary to gregarious, subspherical, brown to black, base immersed in host tissue, with long neck protruding above plant tissue; ascomatal wall consisting of several layers of brown cells of textura angularis. Paraphyses intermingled among asci, unbranched, septate. Asci 8-spored, hyaline, subcylindrical to clavate, unitunicate, short-stipitate, with prominent apical ring. Ascospores bi- to multiseriate in asci, hyaline, guttulate, smooth-walled, fusiform, curved with rounded ends, transversely 3-septate, slightly constricted at septa. Conidiophores solitary or in fascicles, subcylindrical, erect, brown, smooth, rarely branched, with sympodial proliferation. Conidiogenous cells terminal and intercalary, pale brown, with denticulate conidiogenous loci and rhexolytic secession. Conidia solitary, pyriform to obclavate, narrowed toward tip, rounded at base, 2-septate, hyaline to pale brown, with a distinct basal hilum, sometimes with marginal frill (adapted from Klaubauf et al. 2014).
Culture characteristics: Colonies on MEA white to vinaceous, pale olivaceous grey, smoke grey, or grey, cottony. Colonies on OA iron grey, transparent with greenish olivaceous parts, fuscous black with grey centre or hazel with smokey grey tufts.
Optimal media and cultivation conditions: On OA at 25 °C in dark, or autoclaved barley seeds placed on SNA at 25 °C under near-ultraviolet light (12 h light, 12 h dark).
Distribution: Worldwide.
Hosts: Wide range of monocot plants, including important crops of the Poaceae such as rice, barley, millet, oat and wheat.
Disease symptoms: Leaf spot and blast diseases.
Notes: Pyricularia was recently re-evaluated in a phylogenetic study based on five loci (Klaubauf et al. 2014). In this study, the polyphyletic nature of the genus was resolved introducing eight new genera to accommodate the species of Pyricularia that were not grouped with the type species Py. grisea and Py. oryzae in Pyricularia s. str. Moreover, the family Pyriculariaceae was introduced to accommodate Pyricularia, which was previously considered a member of Magnaporthaceae. Pyriculariaceae, as well as Magnaporthaceae, accommodate mainly plant pathogenic species, some of which are of major importance in agriculture.
Pyricularia oryzae is the causal agent of rice blast disease, which can result in up to a 30 % yield loss worldwide (Skamnioti & Gurr 2009). In a phylogenetic study based on 10 loci and 128 isolates of this species, three major clades were identified (Castroagudín et al. 2016). The first clade grouped the isolates associated only with rice and corresponds to the previously described rice blast pathogen Py. oryzae pathotype Oryza. The second clade accommodated isolates associated almost exclusively with wheat and corresponds to the previously described wheat blast pathogen Py. oryzae pathotype Triticum. A third clade accommodated isolates obtained from wheat as well as other Poaceae. This clade was distinct from Py. oryzae and represented a new species, Pyricularia graminis-tritici. This new species could not be morphologically distinguished from Py. oryzae, but a distinctive pathogenicity spectrum was observed (Castroagudín et al. 2016). However, the “oryzae” clade consists of various populations specific to different grass hosts that appear to be in the process of speciation. Consequently, the species in the “oryzae” clade are not commonly accepted, and some authors refer to them as lineages of Py. oryzae (Castroagudín et al. 2017). Further research is needed to resolve speciation within what is presently circumscribed as Py. oryzae.
The sexual morph has been reported only in Py. grisea and Py. oryzae, both being heterothallic species. These are indistinguishable in conidium, perithecium and ascospore morphology. However, Py. oryzae was described as a new species distinct from Py. grisea based on DNA sequence differences in three different loci (act, cal and tub) and host range, since Py. grisea infects only crab grass (Couch & Kohn 2002).
References: Klaubauf et al. 2014 (morphology and phylogeny); Castroagudín et al., 2016, Castroagudín et al., 2017 (morphology, pathogenicity and phylogeny); Reges et al. 2016 (pathogenicity and phylogeny).
Authors: Y. Marin-Felix & P.W. Crous