Alternaria tenuissima (Kunze) Wiltshire, Trans. Br. mycol. Soc. 18(2): 157 (1933), Index Fungorum Number: IF280005
Basionym: Helminthosporium tenuissimum Kunze [as‘Helmisporium’], in Nees & Nees, Nova Acta Phys.- Med. Acad. Caes. Leop.-Carol. Nat. Cur. 9: 242 (1818)
Pathogenic or saprobic on wide range of hosts. Sexual morph: Undetermined. Asexual morph: Sporodochia dark, moderately dense. Conidiophores 60–135 × 4.4–6.7 μm (x = 105 × 5.4 μm, n = 20), simple or branched, straight or flexuous, pale, olivaceous or golden brown, smooth, septate, with one or several sympodially arranged conidiogenous loci. Conidiogenous cells mono- to polytretic, integrated, terminal, later becoming sympodial. Conidia in vivo: 22– 58 × 8–14(−16) μm (x = 37.5 × 11.7 μm, n = 35), simple or branched chains, obclavate, obpyriform, ovoid or ellipsoidal, often with a short conical or cylindrical beak, pale to mid dark brown, with cicatrized black scars at the beaked end, up to 7 transverse and usually several longitudinal or oblique septa, slightly constricted near some septa, finely verruculose; in vitro: 13–29.2 × 6.1–11.8 μm (x = 21.2 × 8.2 μm, n = 30), obclavate, obpyriform, ovoid or ellipsoidal, sometimes subsphaerical, pale to dark brown, up to 5 transverse and usually several longitudinal or oblique septa, slightly constricted near some septa, finely verruculose.
Culture characteristics: Conidia germinating on PDA within 18 h and germ tubes produced from one or several septa. Colonies on PDA reaching 36 mm diam. After 4 days at 25 °C, flat, circular, dense, initially white, becoming light olivaceous brown, surface smooth, with entire to slightly undulate edge.
Material examined: ITALY, Province of Forlì-Cesena, Ravaldino in Monte – Forlì, dead branches of Tamarix gallica L. (Tamaricaceae), 28 March 2014, Erio Camporesi IT1785A (MFLU 14–0600, reference specimen designated here), living culture MFLUCC 14–0441, ICMP 20706
Notes: Alternaria tenuissima (Kunze) Wiltshire is a common pathogen on a wide range of hosts with a worldwide distribution (Gannibal et al. 2007; Rahman et al. 2002; Luan et al. 2007). This species belongs to the section Alternata, which comprises almost 60 species and the molecular variation within this section is low (Woudenberg et al. 2013). The type specimen cannot be located hence we designate the current specimen as a reference specimen with molecular data (Ariyawansa et al. 2014b).
FIG Alternaria tenuissima (MFLU 14–0600) a Appearance of sporodochia on host surface b, c, i Conidiophores and developing conidia d-g, j-l Conidia (i-l from MFLUCC 14–0441) h Germinating conidia. Scale bars: b, c = 25 μm, i = 20 μm, j-l = 10 μm