Pleosporales » Pleosporaceae

Bipolaris

Bipolaris Shoemaker, Can. J. Bot. 37(5): 882 (1959).

Index Fungorum number: IF 7375; Facesoffungi number: FoF 00503, 45 morphological species (Species Fungorum, 2022), 45 species with molecular data.

Asexual morph on PDA: Hyphae hyaline, pale to dark brown or grey. Conidiophores pale to dark brown, single, branched, sometimes arranged in small groups, straight to flexuous or geniculate. Conidiogenous nodes smooth to slightly verruculose. Conidia mostly curved, canoe-shaped, fusoid or obclavate, rarely straight, 3–14-distoseptate (usually more than 6), hyaline, pale or dark brown, reddish brown or pale to deep olivaceous, germinating by production of one or two germination tubes by polar cells. Hilum often slightly protruding or truncate, sometimes inconspicuous. Septum ontogeny first septum median to sub median, second septum delimits basal cell and third delimits distal cell. Sexual morph on Sach's agar and sterilised plant material in culture: Ascomata brown or black, immersed, erumpent, partially embedded or superficial, free or on flat stroma, mostly globose to ellipsoidal, sometimes flask-shaped or flattened on hard substrata, smooth or covered with vegetative filaments. Ostiole central, papillate or with a sub-conical, conical, paraboloid or cylindrical neck. Peridium comprising pseudoparenchymatous cells of equal thickness or slightly thickened at apex. Hamathecium comprising septate, filiform, branched pseudoparaphyses. Asci 2–8-spored, clavate, cylindrical-clavate or broadly fusoid, straight or slightly curved, thin-walled, bitunicate, fissitunicate, often becoming more or less distended prior to dehiscence, short pedicellate, rounded at apex. Ascospores fasciculate, filiform or flagelliform, hyaline or sometimes pale yellow or pale brown at maturity, septate, helically coiled within ascus, degree of ascospore coiling moderate to very strongly coiled, sometimes with free ends, often with a thin mucilaginous sheath (Adapted from Manamgoda et al., 2012; 2014).

 

Type species: Bipolaris maydis (Y. Nisik. & C. Miyake) Shoemaker  

 

Notes: Bipolaris was introduced by Shoemaker (1959) with B. maydis as type species. Bipolaris is characterized by pale to dark brown conidiophores, smooth to slightly verruculose conidiogenous nodes, curved, canoe-shaped, fusoid or obclavate hyaline conidia with slightly protruding or truncate hilum. The sexual morph is characterized by brown or black, immersed, erumpent ascomata, septate, filiform, branched pseudoparaphyses, clavate, cylindrical-clavate or broadly fusoid, straight asci and filiform or flagelliform, hyaline or pale yellow or pale brown ascospores sometimes with thin mucilaginous sheath. Drechsler (1934) reported the sexual morph of Bipolaris as Cochliobolus and is now linked with the type species of Bipolaris, B. maydis (Rossman et al., 2013a).  Although Cochliobolus (1934) is the oldest name, Bipolaris (1959) is mostly used by mycologists and this was approved by the International Commission on the Taxonomy of Fungi (Rossman et al., 2013a). The type species of Bipolaris, B. maydis (≡ Helminthosporium maydis) was chosen over Helminthosporium maydis and a neotype was designated to safeguard the taxonomy of the genus (Rossman et al., 2013b). Members of Bipolaris was previously accommodated in Helmisporium (Link, 1809). Persoon (1822) changed the name Helmisporium to Helminthosporium and this was consequently accepted by Link (1824) and several authors. In the phylogenetic analyses of Berbee et al. (1999), some Bipolaris taxa clustered with Curvularia with two clades Cochliobolus group 1, comprising the type of Bipolaris, B. maydis (Bipolaris sensu stricto) and Cochliobolus group 2, consisting the generic type of Curvularia, C. lunata. Bipolaris resembles Curvularia in having sexual morphs in Cochliobolus. Manamgoda et al. (2014) revised Bipolaris, provided a phylogeny based on ITS, GAPDH and TEF gene sequences and accepted 47 species. The sexual morph of Bipolaris is very rare in nature but it can be produced under laboratory conditions (Nelson, 1964; Paul & Parbery, 1966; Alcorn, 1978, 1990; Tsuda & Ueyama, 1985; Manamgoda et al., 2014). In the phylogenetic analyses of Berbee et al. (2000) based on ITS and GAPDH sequence data, Bipolaris formed a distinct clade distant from similar genera such as Drechslera. Similar results were reported by Manamgoda et al. (2012) based on multigene analyses of LSU, ITS, GAPDH and TEF sequence data. Since then, several species namely plant pathogen have been added to Bipolaris while most human pathogens are found in Curvularia (da Cunha et al., 2013; Madrid et al., 2014). Bhunjun et al. (2020) studied the efficiency of different DNA barcodes in species delimitation in Bipolaris by phylogenetic analyses, Automatic Barcode Gap Discovery and Objective Clustering and accepted 45 species. Bipolaris is morphologically and phylogenetically a distinct genus in Pleosporaceae. Molecular data available for Bipolaris include LSU, SSU, ITS, TEF and GAPDH. GAPDH is the best single marker for Bipolaris (Bhunjun et al., 2020).

 

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