Thaxteriellopsis obliqus M. Niranjan and V.V. Sarma, sp. nov.
Index Fungorum number: IF 557437; MycoBank number: MB 557437; Facesoffungi number: FoF 06266; Figs. 29, 30
Etymology: With reference to an oblique septum in the ascospores.
Holotype: AMH-10087.
Saprobic on decaying Nauclea gageana. Sexual morph: Ascomata 140–190 × 240–345 μm, superficial, with black subiculum, oblate to spheroid, dark brown, scattered, ostiolate, periphysate, velvety, hyphal appendages laterally surrounding ascoma, sparse, flexuous, thick-walled, brown, septate. Necks 80 × 100 μm, depressed when dry, narrow towards apex. Peridium up to 25 μm wide, composed of several layers of outer brown and inner hyaline cells of textura angularis, with guttules. Hamathecium composed of 1–2 μm wide, filamentous, septate, unbranched, anastomosing trabeculate pseudoparaphyses. Asci 67–78(–80) × 15.5–19 μm (x̅ = 74.5 × 17.5 μm, n = 25), 8-spored, bitunicate, cylindric-clavate, apically rounded with an ocular chamber, narrowing towards base, short pedicellate. Ascospores 22–29 × 4.0–5.5 μm (x̅ = 24.8 × 4.8 μm, n = 25), hyaline, triseriate, obclavate-cylindrical, gently curved, obtuse at both ends, apex broader than base, 6–8(–9) trans-septa, rarely muriform with one longitudinal septum which is oblique, not constricted at septa, mature spores becoming grey, smooth walled. Asexual morph: Hyphomycetous, helicosporous, Conidiophores erect, straight or somewhat bent, macronematous, mononematous, superficial, cylindrical, arising as lateral branches from hyphae, branching into whorls, septate, slightly constricted at septa, 170–200 × 6.0–8.5 μm, dark brown to brown, narrowing towards apex, smooth-walled. Each conidiophore bearing 2 to 5 branches of verticels (in whorls) along stipe at intervals (30–45 μm), each whorl having 3 to 5 brown branches. Each branch is 1–4 celled, brown to dark brown, 3–7 μm. Terminal cell of these branches is conidiogenous. Conidiogenous cells holoblastic, mono- to polyblastic, integrated, sympodial, terminal, cylindrical, 3.5–6.5 × 2–2.5 μm, pale brown, denticulate, smooth-walled. Conidia hyaline, solitary, acropleurogenous, helicoid, 12–15 × 9–11.5 μm (x̅ = 13.3 × 9.8 μm, n = 25), conidial filament, coiled 1 to 1½ times, rounded, obtuse end, 3–5 septate, without constrictions, guttulate, smooth-walled, arising on small denticles.
Cultural characteristics: Ascospores germinating on water agar within 24 h and two germ tubes produced at end cells. Colonies growing on MEA, cottony, sterile mycelium, initially grey-brown, become dark brown at maturity, reaching 18 mm in 1 week at 28 °C, mycelium superficial, raised at center, radially straight to undulated edges, septate, unbranched, brown coloured hyphae.
Material examined: INDIA, Andaman and Nicobar Islands, South Andaman, Chidiyatapu Reserve Forest (11°29′52.8″ N, 92°42′38.6″ E). Recorded on Nauclea gageana, 20 May 2018, M. Niranjan & V.V. Sarma (PUFNI 18,727). Herbarium submitted in Ajrekar Mycological Herbarium-AMH (AMH-10087) and NFCC-4429 (holotype) deposited at National Fungal Culture Collection of India (NFCCI), Pune.
GenBank numbers: ITS: MK981534; LSU: MK981533; TEF1: MK984839.
Notes: Thaxteriellopsis obliqus produces ascospores with one or few vertical/oblique septa similar to Chaetosphaer ulina spp. (Crane et al. 1998; Lu et al. 2018d). However, most of the Chaetosphaerulina members have multiseptate ascospores that are more than 10 septate excepting C. eucalypti, which has 6–10 septate ascospores with few vertical or oblique septa. T. obliqus, however, differs from C. eucalypti by having prominent necks with periphyses, narrower and smaller ascomata, smaller asci and smaller ascospores that lack constrictions at the septa. Molecular sequence data of Chaetosphaerulina spp. are not available in the public domain to be included in our phylogenetic analysis for a comparison. The phylogenetic tree also shows that T. obliqus branches separately from T. lignicola with good bootstrap support of 100% in ML, 100% in MP and 1.00 in PP (Fig. 31). T. lignicola is known to produce a Moorella-like anamorph (Subramanian and Sekar 1982). A similar anamorph is found in T. obliqus also. T. obliqus produces ascospores that are 6–8(–9) septate without constrictions at the septa unlike T. lignicola which produces 5-septate ascospores that have constrictions at the septa. Furthermore, T. obliqus differs from T. lignicola in having a central, ostiolated neck in the ascomata, and narrower ascospores with a vertical or oblique septum. In contrast, T. lignciola produces non-ostiolate ascomata. Hence a new species, T. obliqus, is added to the genus.
Fig. 29 Thaxteriellopsis obliqus (NFCC-4429, holotype). a Ascomata on host. b Ascomata attached by lateral hyphae. c Section through ascoma. d Peridium. e–g Asci. g–p Ascospores. Scale bars: d = 200 µm, c = 100 µm, d = 50 µm, e–g = 20 µm, g–p = 10 µm
Fig. 30 Thaxteriellopsis obliqus (NFCC-4429, holotype). a Conidiomata on host. b Culture on MEA. c, d Conidiophores. e Conidiogenous cells. f–i Conidia. Scale bars: c, d = 50 µm, e = 20 µm, f–i = 10 µm
Fig. 31 Maximum parsimony tree constructed by ITS, LSU and TEF1 sequences of species in Tubeufiaceae along with Thaxteriellopsis obliqus (NFCC-4429). Botryosphaeria dothidea CBS 1154.76 served as the out-group. Bootstrap support values for maximumlikelihood (ML), maximum parsimony (MP) and Bayesian posterior probabilities (PP) values ≥ 65% are given above the nodes. Highlighted letter ‘a’ represents the country Thailand