Dothideales » Gnomoniaceae » Plagiostoma

Plagiostoma salicellum

Plagiostoma salicellum (Fr.) Sogonov, Stud. Mycol. 62: 73 (2008)

Index Fungorum number: IF 512203; Facesofungi number: FoF 05761

Saprobic on dead branches of Salix caprea. Sexual morph: Ascomata 205–350 9 260–330 μm (x̄ = 275  ×  290.5 μm, n = 6), perithecial, mostly solitary, scattered, immersed in bark, producing a faint elevation of the periderm, each comprising of a convergent, protruding neck, black, subglobose. Neck 110–120 μm long (x̄ = 113 μm, n = 6), 76–126 μm diam. at the base (x̄ = 97.3 μm, n = 6) and 88–131 lm diam. at apex (x̄ = 103.8 μm, n = 6), cylindrical, eccentric to lateral, straight to very slightly twisted, not surrounded by stroma. Peridium 18–29 μm wide, thick, comprising 4–6 layers, outer layer heavily pigmented, thick-walled, consisting of dark brown to blackish cells of textura angularis, cells towards inside lighter, inner layer composed of 1–2 layers, pale brown to hyaline, flattened, thin-walled cells of textura angularis. Asci 32–55 × 5–15 μm (x̄ = 43.7  × 8.7 μm, n = 34), 8-spored, cylindrical to clavate, clavate-elongated, straight to slightly curved, broadly rounded apex with a conspicuous J- refractive apical ring, 1.7–4.3 μm diam., often consisting of a short but not necessarily persistent, tapered and pointed stipe. Ascospores 12–18 × 1–4 μm (x̄ = 15.8  × 2.5 μm, n = 54), obliquely parallel or irregularly seriate, hyaline, ellipsoid-elongated, tapering slightly towards rounded ends, 1-septate, slightly constricted at median to sub-median septum, with granular cytoplasm, without any sheath or appendage. Asexual morph: Undetermined.

Material examined: ITALY, Province of Forlı`-Cesena [FC], Monte Fumaiolo, on a dead aerial branch of Salix caprea L. (Salicaceae), 27 August 2017, Erio Camporesi, IT 3454 (MFLU 17-1601).

GenBank: ITS: MK080111, TEF1-a: MK424970, TUB2: MK424971.

Notes: Plagiostoma salicellum is characterized by a cylindrical neck surrounded by a white stroma and narrow ellipsoid-elongated ascospores often having short appendages (Meji`a et al. 2011). However, in our specimen no stroma was observed around the perithecial neck which was also shorter x̄ = 113 μm (this study) vs x̄ = 177 μm (Meji`a et al. 2011)] and broader both at the base x̄ = 97.3  μm (this study) vs x̄ = 81  μm (Meji`a et al. 2011)] and at the apex x̄ = 103.8  μm (this study) vs x̄ = 79  μm (Meji`a et al. 2011)] as compared to the lectotype and epitype of P. salicellum described by Meji`a et al. (2011). The perithecia were mostly solitary rather than aggregated and narrower in diameter x̄ = 290.5 μm (this study) vs x̄ = 397 μm (Meji`a et al. 2011)]. The asci also were shorter and narrower (x̄ = 43.7 9 8.7 μm (this study) vs x̄ = 55.0 9 13.0 μm (Meji`a et al. 2011)]. The ascospores of P. salicellum (MFLU 17-1601) did not have an appendage unlike those of the lectotype and epitype of P. salicellum and they were smaller x̄ = 15.8 9 2.5 μm (this study) vs x̄ = 18.5 9 3.5 μm (Meji`a et al. 2011)]. However, the length of the ascospores may not be a key distinguishing factor since Meji`a et al. (2011) observed that length and width of ascospores of P. salicellum may vary, even within an ascus. The combined data set of ITS, TUB2 and TEF1-a sequences in our phylogenetic analyses has not clearly separated our strain (MFLU 17-1601) with significant bootstrap support from the strains of P. salicellum (AR 3828) and (LCM 449.01). The morphological differences mentioned above may be the result of phenotypic plasticity arising from a need to adapt to the climatic conditions in Italy (Jeewon & Hyde 2016). Due to lack of significant molecular support, we, therefore, report our strain as P. salicellum, collected for the first time from Italy.