Bipolaris maydis (Y. Nisik. & C. Miyake) Shoemaker, Canad. J. Bot. 33: 882 (1959).
Basionym: Helminthosporium maydis Y. Nisik. & C. Miyake, Journal of Plant Protection, Tokyo13: 20 (1926).
≡ Drechslera maydis (Y. Nisik. & C. Miyake) Subram.& B.L. Jain, Curr. Sci. 35: 354 (1966)
= Helminthosporium maydis Brond., Ill. Iconogr. Microscop.Cryptog. France 15. 1856–1857 (as ‘Helmisporium’), nom. rej.prop. (Rossman, Manamgoda & Hyde, 2013b)
= Ophiobolus heterostrophus Drechsler in J. Agric. Res. 31: 701. 1925, nom. rej.prop (Rossman et al., 2013b)
= Cochliobolus heterostrophus (Drechsler) Drechsler, Phytopathology 24: 973 (1934).
Pathogenic or saprobic on wood and dead herbaceous stems or leaves. Sexual morph of Bipolaris luttrellii on Sach’s agar medium: Ascomata 260–370 µm (x̅ = 316 µm, n = 10) diam., superficial or slightly immersed, black, sub globose to ellipsoidal. Ostiole, sub conical to campanulate, ostiolar beak and upper part of ascomata covered by densely arranged setae. Pseudoparaphyses filiform, hyaline, septate. Asci 140–205 µm × 18–26 µm (x̅ = 178 × 22 µm, n = 20), 1–8 spored, bitunicate, fissitunicate, hyaline, sub cylindrical, short pedicellate. Ascospores 180–285 × 6–8 µm (x̅ = 235 × 7 µm, n = 20), filiform, hyaline, tapered slightly towards apex and base, tightly coiled inside ascus, sometimes slightly coiled to straight at upper most part, (7–)8(–12)-distoseptate. Asexual morph of Bipolaris maydis on PDA: Conidiophores 105–470 × 5–7 µm (x̅ = 286 µm, n = 20), usually arising singly or in small groups, simple or rarely branched, septate, straight or flexuous, geniculate at upper part,olivaceous brown. Conidiogenous nodes dark brown, distinct. Occasionally secondary sporulation observed. Conidia 66–102 × 14–18 µm (x̅ = 94 × 16 µm, n = 40) µm, pale to mid dark brown, smooth, slightly curved, fusiform, distoseptate. Hilum distinct, 3–5 µm wide, germination tubes arising from both ends of conidia.
Material examined: AUSTRALIA, on Dactyloctenium aegyptium, 3 June1985, J.L. Alcorn, (BRIP 14791, holotype of dried culture of Cochliobolus luttrellii) and USA, North Carolina, isolated from Zea mays?, Olin Yoder C5, resulting from six crosses, culture sporulating on Zea mays (BPI 892696, neotype of Bipolaris maydis).
Notes: Bipolaris was introduced by Shoemaker (1959) and it is considered an important plant pathogen associated with over 60 host genera (Sivanesan 1987; Manamgoda et al. 2011; Agrios 2005; Manamgoda et al. 2012). Cochliobolus Drechsler (1934) is the sexual stage of Bipolaris. There was no clear morphological boundary between the asexual genera Bipolaris and Curvularia, and some species show intermediate morphology which thus caused confusion for many plant pathologists and mycologists for their correct identification (Sivanesan 1987; Manamgoda et al. 2011; Hyde et al. 2014). Based on combined gene analysis of rDNA ITS (internal transcribed spacer), LSU, GPDH and EF1-α, Manamgoda et al. (2012) resolved the taxonomic confusion in Bipolaris and Curvularia complex. Multilocus phylogeny showed that Bipolaris and Curvularia form two well supported clades in previous studies (Manamgoda et al. 2011, 2012) as well as in the present study. Further, the nomenclatural conflict in this complex was resolved giving priority to the more commonly used established generic names Bipolaris and Curvularia thus Cochliobolus was synonymised under Bipolaris. Recently Manamgoda et al. (2014) revised the genus Bipolaris based on DNA sequence data derived from living cultures of fresh isolates, available ex-type cultures from worldwide collections and observation of type and additional specimens. They accepted 47 species in the genus Bipolaris and clarify the taxonomy, host associations, geographic distributions and species’ synonymies while epi- or neotypes were designated for Bipolaris cynodontis, B. oryzae, B. victoriae, B. yamadae and B. zeicola.
In our phylogeny, Bipolaris forms a robust clade sister to Curvularia and Porocercospora. Therefore we accept Bipolaris as a well established genus in Pleosporaceae based on both morphology and phylogeny.
Fig 1. a-h: Bipolaris luttrellii (holotype of dried culture of Cochliobolus luttrellii, j-n), Bipolaris maydis (neotype of Bipolaris maydis, a-h) a. Ascomata on host substrate. b. Section of the ascomata. c. Close up of the peridium d-e. Sub-cylindrical asci with a short pedicle note: helical arrangement of the ascospores j. Conidiophore. k-n. Conidia. Scale bars: b = 100 µm, c = 10 µm, d-g = 60 µm, h-j= 30 µm.
