Pleosporales » Leptosphaeriaceae

Alternariaster

Alternariaster Simmons, CBS Diversity Ser. (Utrecht) 6: 667 (2007).

Index Fungorum number: IF 505049; Facesoffungi number: FoF 01154, 4 morphological species (Species Fungorum 2022), 4 species with molecular data.

Pathogenic on leaves of Helianthus annuus or saprobic on stems and leaves in terrestrial habitats. Sexual morph: Ascomata solitary or in groups of 2– 10, erumpent through host tissue, semi-immersed or nearly superficial, uniloculate, globose to subglobose, coriaceous, black, ostiolate. Ostiole periphysate, papillate, black. Periphyses cellular, aseptate, wide, with a blunt apex, hyaline. Peridium composed of 5–10 rows of scleroplectenchymatous cells, outer part thin, amorphous and black, central part widest, comprising thick-walled cells of textura globularis, inner layer composed of flattened cells of textura angularis. Hamathecium comprising 3–4 μm wide, hyaline, distinctly septate, branched, cellular pseudoparaphyses, embedded in a gelatinous matrix. Asci 8-spored, bitunicate, fissitunicate, cylindrical to cylindric-subclavate, with a short bulbous pedicel, rounded at the apex. Ascospores fasciculate, filiform, multiseptate, constricted at the apical septum, apical cell swollen, conical, yellowish brown, smooth-walled, with a mucilaginous cap (adapted from Ariyawansa et al. 2015) Asexual morph: Lesions on living leaves starting as dispersed punctiform spots, occurring throughout the leaf blade, becoming subcircular to irregular in shape, yellowish, surrounded by a halo of dark green tissue, at the later stages lesions coalesce, resulting in leaf blight and premature plant death. Conidiophores solitary or in small groups, hypophyllous, straight to slightly sinuous, simple, 3–6-septate, pale to chestnut-brown, smooth. Conidiogenous cells yellowish to pale brown, tretic, integrated, terminal to intercalary, sympodial, cylindrical. Conidiogenous cells with conspicuous scars, 1–2 per cell, protuberant, up to 5 μm diam., thickened and darkened. Conidia subhyaline to pale brown, dry, solitary, cylindrical to subcylindrical, occasionally with cells of different sizes, apex and base rounded, transversally 5–9-septate (1–2 longitudinal or oblique septa), often deeply constricted at septa, eguttulate, smooth-walled, hilum thickened and darkened. Germ tubes orientated perpendicularly to the main axis of the conidium, and also polar (adapted from Alves et al. 2013).

    Type species: Alternariaster helianthi (Hansf.) E.G. Simmons

             Notes: Alternariaster is characterised by punctiform spots on living leaves, pale to chestnut-brown, smooth conidiophores, and subhyaline to pale brown, dry, solitary, cylindrical to subcylindrical conidia. Alternariaster differs from Alternaria in conidial morphology especially cylindrical, ellipsoid or broadly ovoid, subhyaline to greyish brown conidia, seldom forming longitudinal or oblique septa and not formed in chains (Alves et al. 2013). Alves et al. (2013) added Alternariaster bidentis to the genus and reported that Alternariaster is a well-defined genus in Leptosphaeriaceae rather than Pleosporaceae. Ariyawansa et al. (2015) described the sexual morph of Alternariastercentaureae-diffusae based on phylogenetic analysis of combined dataset of ITS, SSU and LSU sequence data. Hyde et al. (2017) added Alternariaster trigonosporus based on combined ITS and LSU sequence data. Alternariaster is morphologically and phylogenetically a distinct genus in Leptosphaeriaceae. Molecular markers available for Alternariaster are ITS, LSU, SSU, BTUB, GAPDH and RPB2.

 

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