Atradidymella M.L. Davey & Currah, Am. J. Bot. 96(7): 1283 (2009).
Index Fungorum number: IF 511986; Facesoffungi number: FoF 11782, 1 morphological species (Species Fungorum 2022), 1 species with molecular data.
Pathogenic on host. Sexual morph: Pseudothecia minute (< 200 μm), dark brown, uniloculate, subglobose to pyriform, setose around ostiole, with pseudoparenchymatous walls. Hamathecium pseudoparenchymatous in young ascomata, persisting as septate filamentous remnants in mature ascomata. Asci bitunicate, IKI-negative, 8-spored, cylindrical to clavate. Ascospores brown, fusiform,uniseptate, slightly constricted at septum. Asexual morph: Phoma (adapted from Davey and Currah 2009).
Type species: Atradidymella muscivora M.L. Davey & Currah
Notes: Atradidymella has a sexual morph characterised by dark brown, uniloculate, subglobose to pyriform pseudothecia, cylindrical to clavate asci and brown, fusiform,uniseptate ascospores. Atradidymella resembles Coleroa, Didymella, Didymosphaeria, Phaeodothis, Roussoëlla and Venturia in having reduced stromata, darkly pigmented pseudothecia and fusiform,uniseptate ascospores. Atradidymella can be differentiated from these genera based on ascospore and pseudothecium morphology and stroma features. Atradidymella has smooth, darkly pigmented ascospores without a gelatinous sheath, while Phaeodothis has pigmented, sheath-bearing ascospores, Didymella has hyaline ascospores and Roussoëlla has reticulately or striately ornamented ascospores (Aptroot 1995). Atradidymella produces a compact stroma within only one host cell, from which the pseudothecium arises while Coleroa and Venturia form broader stromata that originate both inter- and intracellularly in the epidermal and subepidermal areas of the host (Barr 1968). Atradidymella differs from Didymosphaeria in having tiny pseudothecia and a pseudoparenchymatous peridium while Didymosphaeria has larger pseudothecia and a hyphal peridium comprising cells of textura intricata (Aptroot 1995). Atradidymella resembles Phaeodothis in having small pseudothecia and reduced stromata but can be differentiated in that the latter has fewer peridial layers (2–3 in Atradidymella, 1–2 in Phaeodothis). The asexual morph of Atradidymella is Phoma (Davey and Currah 2009). Didymosphaeria (Farr et al. 1989), Massarina (de Hoog 1979) and Otthia (Grove 1935) are sexual genera with fusiform, pigmented, uniseptate ascospores which have a Phoma or Ascochyta asexual morph but these genera are phylogenetically distinct from Atradidymella. The taxonomic placement of Atradidymella is doubtful and is currently placed in Pleosporales genera incertae sedis. More collections are needed to confirm the taxonomic position of the genus. Only ITS sequence data is available for Atradidymella.
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