Acroconidiella
Acroconidiella J.C. Lindq. & Alippi, Darwiniana 13 (2–4): 612 (1964).
Index Fungorum number: IF 7030; Facesoffungi number: FoF 06629, 5 morphological species (Species Fungorum 2022), no molecular data available.
On fruits or leaves forming irregular to subcircular brownish or purple amphigenous spots joining and causing blight of large areas of the leaf with yellow periphery. Sexual morph: Unknown. Asexual morph: Colonies mainly hypophyllous. Mycelium immersed, branched, septate, hyaline, smooth. Conidiophores arising singly or in small groups through stromata or breaking through epidermis, erect, flexuous, simple, or occasionally branched, septate, frequently geniculate, sometimes slightly swollen at the apex, pale to mid olivaceous brown, smooth, conidial scars similar to those formed in Drechslera and Curvularia. Conidiogenous cells polytretic, integrated, terminal, subcylindrical to cylindrical, occasionally geniculate with sympodial proliferation with one locus on a broadly obtuse apex, with a pigmented alternarioid scar. Conidia tretic, solitary or in short (2–3) unbranched chains, ellipsoidal, lacking longitudinal septa, (1–)2(−3) transverse septa, strongly constricted at the septa, olivaceous brown, thin-walled, verruculose (adapted from Ferreira & Barreto 2019).
Type species: Acroconidiella tropaeoli (T.E.T. Bond) J.C. Lindq. & Alippi
Notes: Acroconidiella is characterised by macronematous, mononematous, simple, or occasionally branched conidiophores with integrated, terminal, polytretic sympodial conidiogenous cells producing solitary ellipsoidal, septate, echinulate conidia (Ellis 1971). Baker (1947) previously reported a disease symptom in Tropaeolum majus (Tropaeolaceae) in California and thought that the fungus belongs to Heterosporium. Consequently, Bond (1947) described the fungus on Tropaeolum majus in Ceylon (Sri Lanka) as Heterosporium tropaeoli. De Vries (1952), reported that Heterosporium should be considered similar to Cladosporium. The fungus defined as Heterosporium tropaeoli resembles Cladosporium in having porospores instead of blastospores but differs in having a scar morphology distinct from those of Cladosporium. Lindquist and Alippi (1964) reported that H. tropaeoli is closer to Alternaria, than to Curvularia and Cladosporium however, H. tropaeoli did not produce muriform conidia in chains, which was the main diagnostic feature for Alternaria, at that time. Subsequently, Lindquist and Alippi (1964) proposed the new genus Acroconidiella to accommodate this fungus and labelled it Acroconidiella tropaeoli. Vieira and Barreto (2002) reported that Acroconidiella produces short acropetal conidial chains in vitro and several non-dictioconidial species as those belonging to Alternaria. Prasher and Verma (2015) provided morphological comparison of Acroconidiella species. Ferreira and Barreto (2019) reappraised the genus Acroconidiella to confirm the observations made by previous authors. Ferreira and Barreto (2019) re-collected samples of Acroconidiella tropaeoli, and also of Acroconidiella trisepta, from Brazil and performed morphological and a molecular phylogenetic analysis. The authors concluded that Acroconidiella is an artificial genus which is now rejected, because its type species belongs to Alternaria which has nomenclatural priority over Acroconidiella. Ferreira and Barreto (2019) proposed the new name Alternaria obtusa for Acroconidiella tropaeoli because a combination into ‘Alternaria tropaeoli’ was not possible due to the name being already in use for another valid (and distinct) species in the genus described from India on T. majus. Other species currently placed in Acroconidiella, need revision to decide their correct taxonomic affinity. The lack of molecular data makes further studies in Acroconidiella challenging. Hongsanan et al. (2020a) did not consider the observations made by Ferreira and Barreto (2019) and included Acroconidiella in Cladosporiaceae. Recollection, isolation and re-assessing species in the genus Acroconidiella is needed. We follow Ferreira and Barreto (2019) and transfer Acroconidiella in Dothideomycetes genera incertae sedis until further confirmation.
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