Taxonomy
Digitodesmium polybrachiatum T.F. Nóbrega, B.W. Ferreira and R.W. Barreto, sp. nov. (Fig. 2)
MycoBank: MB839275
Holotype: BRAZIL: ESPÍRITO SANTO, NOVA VENÉCIA: on dead wood of Coffea canephora, July 09, 2020, T. F. Nóbrega (holotype VIC 47492).
Ex-holotype cultures COAD 3174 and COAD 3175. DNA sequences of ex-holotype strain: MW879325 (SSU), MW879316 (LSU), MW879318 (ITS), MW890262 TEF1.
Etymology
In reference to its numerous conidial arms.
Description:
Saprobic on dead wood of Coffea canephora. Sexual morph Unknown. Colonies punctiform, scattered, glistening dark brown to black. Conidiomata sporodochial, scattered, dark brown. Conidiophores micronematous, subcylindrical, 4–8 × 4–5 µm, unbranched, thin walled, hyaline to pale brown, smooth. Conidiogenous cells monoblastic, integrated, terminal, determinate, hyaline to pale brown, smooth. Conidia acrogenous, solitary, cheiroid-ellipsoid, 35–54 × 15–19 µm, consisting of 6–9 closely compacted arms, side arms longer than middle arms, arms 7–9-euseptate, septal pores inconspicuous; arms cylindrical, 35–49 × 5–7 µm, straight (inner arms) or slightly curved (outer arms), unbranched, brown to dark brown, smooth, occasionally bearing cellular appendages attached to one of the inner arms. Appendages globose to subglobose, 10–15 × 8–14 µm, either fhin-walled and hyaline or light brown and as thick-walled as conidia, smooth.
Culture characteristics: i) on MEA – very slow-growing, 3.5 cm diam after 40 days; flat, margin strongly lobate outline with immersed dendritic borders, aerial mycelium velvety, umber centrally, bay towards the edge, pigmenting the medium with a luteous taint; no sporulation.; ii) On VBA, very slow-growing, 7 cm diam after 40 days; umbonate with strongly lobate margins. cottony center, white, followed by a ring of felty pale mouse gray mycelium and an external halo of white sparse mycelium, dark with pockets of intense sporulation; reverse sienna centrally with amber margins.
Notes
The isolates obtained in this study had a distinct morphology from the other species described in Digitodesmium (Table 2). Digitodesmium polybrachiatum sp. nov. differs from D. macrospora, D. intermedium and D. heptasporum by having smaller and narrower conidia (35–54 x 15–19 µm vs. 130–145 × 19–26 µm; 39–76 × 25–35 µm and 50–75 × 32.5–70 µm, respectively). Digitodesmium bambusicola, D. chiangmaiense and D. elegans, despite having conidia with similar dimensions to the newly proposed species, have few arms in their conidia as compared to D. polybrachiatum. In addition, in the phylogenetic tree, the isolates of D. bambusicola and D. chiangmaiense were in separate clades to that of D. polybrachiatum. Other characteristics that also help distinguishing D. polybrachiatum from other species in the genus are the occasional presence of isolate globoid appendages on its conidia, which are either hyaline and thin-walled or pale brown and thicker-walled, and the presence of inconspicuous septal pores. Appendices are only known for D. bambusicola and inconspicuous septal pores is only found in D. elegans.
Table 2
Comparison of conidial morphology in species of Digitodesmium
Taxa | Colour | Dimension (µm) | Appendages | Septal pores | Number of arms | Number of septa per arm | Origin | Reference |
D. bambusicola | Pale brown | 24–32.5 × 12.5–23 | Yes | Conspicuous | 3 | 4–7 | Philippines | Cai et al.(2002) |
D. chiangmaiense | Brown to dark brown | (25–)30–45(–44) × (13–)12–21(–21) | No | Conspicuous | 3 | 5–7 | Thailand | Hyde et al. (2019) |
D. elegans | – | 45–60 × 12–21 | No | Inconspicuous | (2–)3–4(–6) | 9–12 | UK | Kirk. (1981) |
D. heptasporum | Pale brown | 50–75 × 32.5–70 | No | Conspicuous | 6–7 | 11–17 | China | Cai et al.(2003) |
D. intermedium | Brown to dark brown | 39–76 × 25–35 | No | Conspicuous | 3–11 | 7–13 | Spain | Silvera-Simo´net al. (2010) |
D. macrosporum | Brown to dark brown | 130–145 × 19–26 | No | Conspicuous | 5–8 | 17–19 | Spain | Silvera-Simo´net al. (2010) |
D. recurvum | Pale brown | 30–45 × 12.5–23 | No | Conspicuous | (2–)4–6(–7) | 6–10 | China | Ho et al.(1999) |
D. polybrachiatum sp. nov. | Brown to dark brown | 35–54 x 15–19 | Yes | Inconspicuous | 6–9 | 7–9 | Brazil | This study |