Chaetosphaeronema Moesz, Bot. Közl. 14: 152 (1915)
Dothideomycetes, Pleosporomycetidae, Pleosporales, Phaeosphaeriaceae
Saprobic on the host plant in terrestrial habitat. Sexual morph: Ascomata dark brown to black, solitary to gregarious or confluent, visible as spots on the host surface, immersed to semi-immersed, globose to subglobose, unilocular, glabrous, thick-walled, papillate, ostiolate. Ostiole single, cylindrical, centrally located. Peridium composed of thick-walled, dark brown to pale brown or hyaline cells of textura angularis. Hamathecium composed of asci and pseudoparaphyses. Pseudoparaphyses hyaline, broad cellular, septate, constricted at septa, branched, smooth-walled. Asci 8-spored, bitunicate, with indistinct ocular chamber, cylindrical to cylindric-clavate, with rounded apex and short pedicel. Ascospores greenish-yellow, overlapping or lying parallel or spiral, without sheath or appendages, septate, inflated at 10th cell, the inflation more pronounced near the 9th septum, apical part bent or curved (description from Ariyawansa et al. 2014). Asexual morph: Conidiomata dark brown to black, pycnidial, solitary to gregarious, immersed to semi-immersed, subepidermal in origin, rostrate, globose to subglobose, unilocular or multi-locular, thick-walled, setose or glabrous, ostiolate. Ostiole single, cylindrical to subcylindrical or conical, straight or curved, with long neck lined with periphyses, covering by dark brown to brown setae. Conidiomtal setae dark brown, restricted to the beak, sparse or numerous, septate, unbranched, straight or curved, blunt at base, attenuated towards the upper part. Periphyses hyaline, hyphae-like, subcylindrical, with obtuse apex, unbranched, septate, smooth-walled, formed from inner wall of ostiole. Conidiomatal wall composed of thick-walled, dark brown to brown or hyaline cells of textura angularis to textura prismatica. Conidiophores arising from the innermost layer of conidiomata, absent or present, when present, hyaline, cylindrical, branched irregularly and only sparingly, septate. Conidiogenous cells hyaline, enteroblastic, phailidic or annelidic, cylindrical to subcylindrical, ampuliform or lageniform, determinate, integrated or discrete, smooth-walled, channel and collarette minute, periclinal wall thickened or percurrent proliferation. Conidia hyaline, cylindrical, with obtuse apex, with blunt and truncate base, 1-septate, smooth-walled, often guttulate.
Notes: Chaetosphaeronema is characterized by dark brown, thick-walled, setose conidiomata with long, papillate ostioles, and hyaline, cylindrical, 1-septate conidia (Sutton 1980). Petrak (1944) synonymized C. herbarum (Hollós) Moesz under the type species, and accepted three species in the genus, namely C. collivagum (Petr.) Petr, C. galii (Petr.) Petr. and C. hispidulum. Sutton (1980) accepted only type species in the genus and provided a detailed description and illustration. De Gruyter et al. (2009) included sequence data (LSU and SSU) of type species in phylogeny analyses, and showed that Chaetosphaeronema was related to Phaeosphaeriaceae. However, strain CBS 826.88 isolated from soil showed characteristics of Phoma betae A.B. Frank and Ascochyta caulina (P. Karst.) Aa & Kesteren (pilose pycnidia, hyaline, ellipsoidal and aseptate conidia), which is distinct from the type species where the setose feature is restricted to the ostiolar region, and conidia are 1-septate (Boerema et al. 2004, De Gruyter et al. 2009). Therefore, it was concluded that strain CBS 826.88 was a misidentification. De Gruyter et al. (2010) added species C. oonsii (≡ Phoma coonsii) based on hair-like setae on conidiomata, together with molecular data of LSU and SSU. However, our phylogenetic analyses of LSU, SSU and ITS sequence data show that C. oonsii has closely affinity with Dematiopleospora alliariae Thambug et al. Chaetosphaeronema oonsii differs from Chaetosphaeronema by its aseptate conidia. Based on both morphology and phylogeny, C. oonsii is excluded from Chaetosphaeronema, and further study on sexual and asexual morphs of these two taxa is needed.
Chaetosphaeronema is associated with sexual morph Ophiobolus (Petrak 1944, Zhang et al. 2009, 2012, Ariyawansa et al. 2014, Rungtiwa et al. 2014), but this sexual and asexual morph connection has not been confirmed, because of limited sequence data. Rungtiwa et al. (2017) revised Ophiobolus and ophiobolus-like taxa and showed that O. cirsii is closely related to Chaetosphaeronema species and distinct from Ophiobolus sensu stricto. Our phylogenetic results are in accordance with Rungtiwa et al. (2017) The LSU sequence of Ophiobolus cirsii (MFLUCC 13-0218) is 100% (873/873) similar to C. hispidulum (CBS 216.75), and ITS sequence is distinguished by two gaps (568/570). The SSU sequence of O. cirsii is problematic after 1105bp length and is not included in the analyses. To provide a natural classification for O. cirsii, we synonymize it under Chaetosphaeronema hispidulum.
Two new collections, C. achilleae (MFLUCC 16-0476) and C. hispidulum (CBS 216.75) with glabrous pycnidia cluster with Ophiobolus cirsii (MFLUCC 13-0218) with strong bootstrap value (99/100/0.99). Combined with morphological characters, these two collections are recognized as conspecific with C. hispidulum. Chaetosphaeronema achilleae is also reduced to a synonym of the type species.
Distribution: Australia, Germany, India, Italy, Japan, Russia (Gruyter et al. 2010, Quaedvlieg et al. 2013, this study).
Li WJ, McKenZie EHC, Liu JK, Bhat DJ, Dai DQ, Caporesi E, Tian Q, Maharachcikumbura SSN, Luo ZL, Shang QJ, Zhang JF, Tangthirasunun N, Karunarathna SC, Xu JC, Hyde KD (2020) Taxonomy and phylogeny of hyaline-spored coelomycetes. Fungal Diversity 100: pages279–801.