Taxonomy
Tuber elevatireticulatum K.F. Wong and H.T. Li, sp. nov. Fig. 1
MycoBank no.: MB824068.
Etymology: Referring to the prominently elevated reticulum on the ascospores.
Ascocarp hypogeous, scattered, solitary, subglobose or irregular, 12–19 mm long × 10–15 mm wide, 0.32–1.7 g in fresh weight, solid, smooth on the surface, whitish to pale yellowish when fresh, becoming light brown at maturity. Peridium two-layered; inner layer 85–425 μm thick, hyaline, composed of intricately interwoven hyphae; outer layer 75–110 μm thick, light brownish, pseudoparenchymatous, composed of globose, subglobose, rod-shaped or angular cells, 5–25 μm diam. Hyphae-like hairs arise from outermost cells, hyaline, septate, tapering towards the ends, acute or round at the apex, 50–275 × 1.25–3.75 μm. Gleba translucent or light-brown, marbled with narrow, white veins when young, becoming dark brown, marbled with narrow, light brown veins at maturity. Asci 1-3(-4)-ascospored, globose, subglobose, ovoid to ellipsoid, 47.5–88 × 37.5–75 µm, hyaline, with a wall 2.5 µm thick. Ascospores broadly ellipsoid to ellipsoid, rarely subglobose and globose, with mature ascospore ratio ranging 0.2–53% (n = 1000), yellowish brown to dark brown, with a wall 2.5–5 µm thick, 32.5–50 × 20–32.5 µm from 1-ascospored asci, 20–48 × 20–32.5 µm from 2-ascospored asci, 20–40 × 20–27.5 µm from 3-ascospored asci, 22.5–35 × 17.5–25 µm from 4-ascospored asci (Q = 1.0–1.75, Q = 1.30 ± 0.19), ornamented with irregular reticulations 2.5–7.5 µm high, with meshes varying in size, mostly 3-4(-5) across the ascospore width.
Specimens examined: TAIWAN, Nantou County, Sitou Tract, associated with roots of K. fortunei var. cyclolepis, 1 Jun 2017, collected by C.-L. Lin, K.-F. Wong, H.-T. Li and F.-Y. Lin, XTAM3 (holotype), ITS sequences: MF540616–MF540621; LSU sequences: LC425119–LC425126.
Notes: Tuber elevatireticulatum grows in montane area of central Taiwan with elevation of 1150 m. It is associated with a cluster of K. fortunei var. cyclolepis in a mixed coniferous plantation, at least 4 m apart from the nearest Cryptomeria japonica (L. f.) D. Don, Chamaecyparis formosensis Matsum. and a few Pinus species which all have no record of association with Tuber species. Ascocarps are mostly scattered and distributed in solitary in loamy soil with pH ranging from 5 to 6. Ascocarps are usually found within 0–2 m from tree trunks, starting to develop in March and maturing in June. Odor is pleasant, mild, peculiar but superb, rarely becoming unpleasant with ageing. The temperature during the ascocarp formation is 20–25 °C.
Phylogenetic analyses
The ITS matrix consisted of 52 sequences and 1661 aligned bases, of which 1198 bp were identified as poorly aligned and were excluded by Gblocks. The resultant ITS alignment was 463 bp. The LSU matrix consisted of 47 sequences and 1519 aligned bases, of which poorly aligned and were excluded by Gblocks and the resultant LSU alignment was 580 bp. As Maximum likelihood and Bayesian analyses yielded similar tree topologies of ITS region, thus the only tree generated form ML analysis is shown in Fig. 2. The ML and Bayesian analyses of LSU region is similar in general, due to the limited availability of sequences in database, the tree inferred form ML analysis is presented in Fig. 3, separate trees are presented as Additional files 1, 2.
There has no significant incongruence among ITS and LSU region of ribosomal DNA. Tuber elevatireticulatum is clearly different from other whitish truffles and formed a monophyletic clade with strong bootstrap (BS) and posterior probability (PP) values (1.00/1.00). Based on the ITS analysis, T. elevatireticulatum was placed clearly in the Puberulum clade, within which it formed a subclade with five Asian species, including T. thailandicum, T. pseudosphaerosporum, T. alboumbilicum, T. latisporum, and T. panzhihuanense, with strong branching supports by BS (0.89) and PP (0.99) value. Also included in the Puberulum clade were T. borchii, T. dryophilum, T. oligospermum and T. sphaerospermum from Europe; T. microsphaerosporum, T. sinopuberulum, T. vesicoperidium, T. lijiangense, T. sinosphaerosporum, T. zhongdianense, T. huizeanum, T. liui and T. liyuanum from China; and T. californicum from the USA. These whitish truffle species formed a subclade within the Puberulum clade with strong PP value of 1.00 and was sister to the one where T. elevatireticulatum was placed. The groupings of whitish truffles were similar from those in Kinoshita et al. (2011), Suwannarach et al. (2015) and Bonito and Smith (2016).