Pyrenophora Fr., Summa veg. Scand., Sectio Post. (Stockholm): 397 (1849).
Index Fungorum number: IF 4596; Facesoffungi number: FoF 000009, 108 morphological species (Species Fungorum, 2022), 16 species with molecular data.
Pathogenic on host. Sexual morph: Ascomata immersed, becoming erumpent to near superficial, solitary or scattered, globose to subglobose, broadly or narrowly conical, smooth-walled, ostiolate. Ostiole papillate, covered with brown to reddish-brown setae, which are darkened at the base. Peridium comprising 2–4 layers of brown, thick-walled cells of textura angularis. Pseudoparaphyses not observed. Asci 8-spored, bitunicate, fissitunicate, clavate to sub-cylindrical, with a short, broad pedicel, with a distinct ocular chamber surrounded by a large apical ring. Ascospores 2–3-seriate, muriform, constricted at the septum, smooth-walled, surrounded by a mucilaginous sheath. Asexual morph: hyphomycetous, Conidiophores macronematous, mononematous, sometimes caespitose, straight or flexuous, often geniculate, unbranched or in a few species loosely branched, brown, smooth in most species. Conidiogenous cells polytretic, integrated, terminal, frequently becoming intercalary, sympodial, cylindrical, cicatrized. Conidia solitary, in certain species also sometimes catenate or forming secondary conidiophores which bear conidia, acropleurogenous, simple, straight or curved, clavate, cylindrical rounded at the ends, ellipsoidal, fusiform or obclavate, strawcoloured or pale to dark brown or olivaceous brown, sometimes with cells unequally coloured, the end cells then being paler than intermediate ones, mostly smooth, rarely verruculose, pseudoseptate (Adapted from Ellis, 1971 and Ariyawansa et al., 2014).
Type species: Pyrenophora phaeocomes (Rebent.) Fr.
Notes: Pyrenophora was introduced by Fries (1849) with P. phaeocomes as type species. Pyrenophora is characterized by immersed, erumpent ascomata, papillate ostiole covered with brown to reddish-brown setae, fissitunicate, clavate to sub-cylindrical asci and 2–3-seriate, muriform ascospores surrounded by a mucilaginous sheath. Pyrenophora was previously described as Sphaeria phaeocomes by Rebentisch (1804) and was accommodated in Xylariaceae. Fries (1849) re-circumscribed the genus as Pyrenophora and accommodated it in Pleosporales. Wehmeyer (1961) treated Pyrenophora in Pleosporaceae based on morphology. Barr (1987) redefined Pleosporaceae and included Clathrospora, Kirschsteiniothelia, Lewia, Pleospora and transferred Cochliobolus, Pyrenophora, Setosphaeria in Pyrenophoraceae. Berbee (1996) did not agree with Barr (1987) and suggested that the genera above belong to Pleosporaceae. The idea of Berbee (1996) has been followed by several authors (Zhang et al., 2012; Hyde et al., 2013). Pyrenophora differs from Pleospora, the type of Pleosporaceae in lacking pseudoparaphyses and having smaller ascospores. Pyrenophora can be differentiated from similar genera such as Clathrospora and Platyspora in having terete ascospores. In the phylogenetic analysis of Zhang and Berbee (2001) based on ITS and GAPDH, Pyrenophora formed a distinct lineage in Pleosporaceae close to Bipolaris and Setosphaeria. Pyrenophora differs from Bipolaris in having filiform ascospores (Wehmeyer, 1953). Pyrenophora has been linked to the asexual morphs in Drechslera (Drechsler, 1923; Shoemaker, 1959, 1961). Taxa in Drechslera were previously placed in Helminthosporium based on the dark color, transversely septate conidia and a graminicolous lifestyle (Drechsler, 1923; Shoemaker, 1959, 1961). Later, the graminicolous Helminthosporium taxa were divided into three genera, Bipolaris, Drechslera, and Exserohilum, on basis of their relationship with their sexual states Cochliobolus, Pyrenophora and Setosphaeria respectively (Zhang & Berbee, 2001). Members of Pyrenophora can be distinguished from Cochliobolus and Setosphaeria based on the shape, septation and color of their ascospores (Zhang & Berbee, 2001). Usually, species exist as anamorphs in the Pyrenophora/Cochliobolus/Setosphaeria group. Ariyawansa et al. (2014) provided an updated account of Pyrenophora based on morphology and phylogenetic analyses of LSU, SSU, ITS, GAPDH, RPB2 DNA sequence and reported that Pyrenophora is a monophyletic genus in Pleosporaceae. Ariyawansa et al. (2014) also synonymized Drechslera under Pyrenophora as the Pyrenophora sexual states clustered with their respective Drechslera asexual states. Pyrenophora is morphologically and phylogenetically a distinct genus in Pleosporaceae but might comprise species complex.
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