Extremopsis radicicola G. Delgado & Maciá-Vicente, sp. nov.
MycoBank number: MB 838946; Index Fungorum number: IF 838946; Facesoffungi number: FoF 11117;
Etymology. Name refers to the roots of the host plant from which the fungus was isolated.
Mycelium composed of hyaline, subhyaline to pale brown, branched, septate hyphae, 2 – 3.5 µm wide. Chlamydospores present, abundant, terminal or intercalary, solitary, in short chains of up to 8 or forming more or less dense clusters, globose, subglobose, ellipsoidal, pyriform or elongated, subhyaline to pale brown, smooth, thin-walled that may become brown, thick- walled, 0 –1-septate and smooth to verruculose, dark brown when forming large clusters, (3 –)4 –11(–13) × 2.5 – 8(–10) µm. Culture characteristics — Colonies on malt extract agar (MEA) slow growing, reaching 9 –13 mm diam after 3 wk at 25 °C, velvety, grey to dark grey or blackish grey, raised 1– 2 mm at the centre, with or without a concentric ring around the raised centre, margin entire, reverse black, no exudates. On potato dextrose agar (PDA) reaching 10 –14 mm diam, dark grey olivaceous, slightly raised at the centre, margin slightly diffuse, reverse black olivaceous. On modiﬁed cellulose agar (MCA) very slow growing, reaching 6 – 8 mm diam, dark grey, grey at the centre, flat, margin irregular, diffuse, reverse black. Cultures sterile, chlamydospores abundant.
Typus. SPAIN, Ciudad Real, Cabañeros National Park, from root-associated soil in a wet heathland (‘trampal’), N39°20’58.5″ W4°21’38.6″, 725 m a.s.l., isolated from surface-sterilised, asymptomatic roots of an Arabidopsis thaliana plant inoculated with soil and grown under controlled conditions, 19 Apr. 2018, coll. J.G. Maciá-Vicente, isol. 20 June 2018, J.G. Maciá-Vicente, P6446 (holotype stored in a metabolically inactive state CBS 147117, culture ex-type CBS 147117, ITS and LSU sequences GenBank MN310191 and MN308483).
Notes — The family Extremaceae includes fungi that are ecologically highly diverse ranging from extremophilic, rock inhabiting and acidophilic members such as Extremus, the generic type, to lichenicolous, epiphyllous, endophytic, saprobic or plant pathogenic genera (Quaedvlieg et al. 2014). The new genus Extremopsis is introduced to accommodate sterile strains of a root endophyte isolated from surface-sterilised, asymptomatic roots of plants used as bait inoculated with root-associated soil. The three strains of E. radicicola did not sporulate in any of the different culture media used including MEA, PDA, MCA or Water Agar supplemented with wooden toothpicks, but they produced abundant chlamydospores in all media. Their ITS and partial LSU sequences were nearly identical except for a single gap at position 128 of alignment in the case of the ITS of both CBS 147117 and P6514, and two bp differences in the LSU of the latter. Phylogenetically, they form a strongly supported monophyletic group in Extremaceae sister to the genus Extremus but with low support. Moreover, although originally identiﬁed as ‘Devriesia’ sp., they group distant from Devriesia s.str. in Teratosphaeriaceae represented by D. stauro- phora, the generic type (Meng et al. 2017). Interestingly, two other strains also named ‘Devriesia’ sp., NG_p52, isolated during a study of gene expression of fungal nitrate reductases in agricultural soils from Austria (Gorfer et al. 2011); and MI63, isolated from soil in Germany, grouped within the Extremopsis clade and seem conspeciﬁc with E. radicicola, expanding the known distribution of the genus from southern Spain to other localities across Europe.
Based on a megablast search of NCBIs GenBank nucleotide database, the closest hits of Extremopsis radicicola (CBS 147117) using the ITS sequence are ‘Devriesia’ sp. NG_p52 (GenBank HQ115717.1; Identities = 232/232 (100 %), no gaps), ‘Devriesia’ sp. MI63 (GenBank MW268825.1; Identities = 230/232 (99 %), no gaps) and a melanised limestone ascomycete CR-2004 TRN80 (GenBank AY559340.1; Identities = 222/232 (96 %), two gaps (0 %)). The closest hits using the LSU sequence are ‘Devriesia’ sp. NG_p52 (GenBank: HQ115717.1; Identities = 488/490 (99 %), no gaps), Extremus adstrictus (GenBank KF310022.1; Identities = 527/539 (98 %), two gaps (0 %)) and ‘Devriesia’ sp. OTU56 TS-2013 (GenBank AB808449.1; Identities = 521/535 (97 %), two gaps (0 %)).