Dendrostoma castaneum (Tul. & C. Tul.) Voglmayr & Jaklitsch

Jaklitsch, Walter M. & Voglmayr, Hermann, 2019, European species of Dendrostoma (Diaporthales), MycoKeys 59, pp. 1-26 : 1

Dendrostoma castaneum (Tul. & C. Tul.) Voglmayr & Jaklitsch comb. nov. Figures 5 , 6

Valsa castanea Tul. & C. Tul., Select. fung. carpol. (Paris) 2: 202 (1863) (Basionym).

≡ Amphiporthe castanea (Tul. & C. Tul.) M.E. Barr, Mycol. Mem. 7: 142 (1978).

≡ Cryptodiaporthe castanea (Tul. & C. Tul.) Wehm., Trans. Br. mycol. Soc. 18(4): 284 (1934) [1933].

≡ Diaporthe castanea (Tul. & C. Tul.) Sacc., Syll. fung. ( Abellini ) 1: 624 (1882).

= Cryptospora leiphaemoides Fuckel, Jb. nassau. Ver. Naturk. 25-26: 323 (1871).

≡ Diaporthe leiphaemoides (Fuckel) Sacc., Syll. fung. ( Abellini ) 1: 624 (1882).

Diagnosis.

Dendrostoma castaneum is recognized by KOH+ purple ostioles, slender ascospores with small drops and subfusiform conidia, and the presence of hyphal conidiophores.

Description.

Sexual morph: pseudostromata 0.8 –3(– 5) mm in their widest dimension in cross section, very variable, flat subconical or lenticular, in outline circular, elliptic or elongate, scattered, gregarious or confluent, and forming elongate patches, lifting the periderm slightly and often becoming visible as a dark zone on the bark surface, causing bumps in bark, splitting the periderm. Ectostromatic discs 0.3-2.7 mm in their widest dimension, often ill-defined and variable, cream, yellowish brown to dark brown, flat, surrounded by bark flaps, first present as a covering layer with ostiolar necks subsequently bursting through it, soon crumbling away. Ostioles 1-25 per disc, usually arising eccentrically from the perithecial venter, (53 –)71–125(– 180) µm (n = 51) in diameter, bluntly conical or cylindrical with black sides and red, yellowish, or greenish tip, often attenuated to a minute, ca 20-40 µm wide dark centre, in section rounded to angular, sometimes sulcate, variably arranged in the disc, projecting to 0.2 mm, periphysate; red colour of the ostiolar tip turning purple in 3% KOH and yellow in lactic acid. Entostroma yellowish to shades of brown, consisting of bark cells and hyaline to yellowish, 1.5-4.5 wide, thin-walled hyphae becoming thicker-walled and forming a pseudoparenchyma in the vicinity of perithecia. Perithecia tightly aggregated, (265 –)305–460(– 600) µm (n = 47) in diameter, depressed subglobose to ellipsoid, collapsing upward; peridium ca 10-30 µm thick, hyaline, pale olivaceous to brown, in section outside of brown isodiametric to strongly compressed thick-walled cells, inside of compressed and elongated hyaline to brownish cells, in combination (3 –)4–15(– 28) µm (n = 57) in diameter. Paraphyses absent at maturity. Asci (49 –)53–63(– 65) × (7.8 –)8.5–10.5(– 12) µm (n = 35), narrowly clavate to subfusoid or oblong, floating freely in the centre, thick-walled at the apex containing a minute refractive ring invisible in 3% KOH, containing 4-8 biseriate ascospores. Ascospores (11.5 –)14–18(– 20) × (3 –)3.5–4.5(– 5.3) µm, l/w (2.7 –)3.5–4.6(– 5.4) (n = 76), 2-celled, not or slightly constricted at the median or slightly eccentric septum, oblong to inequilaterally ellipsoid, straight to mostly curved, with the upper cell often slightly wider than the lower, broadly rounded at the ends, hyaline, with several minute drops (confluent to 2 larger drops per cell in mounts), smooth, with or without a hyaline, subconical to filiform appendage (2.2 –)2.8–4.5(– 5.5) × (1.1 –)1.3–1.6(– 1.8) µm (n = 88) at each end invisible in 3% KOH.

Asexual morph co-occurring with the sexual morph, acervular, pulvinate, scattered to aggregated, 0.5-2.7 mm in diameter, appearing as superficial discs 0.3-2 mm in diameter, with undulate surface, cream to pale brown and becoming brittle in the centre and nearly black at the periphery and often also indicated as dark zone on the bark surface around the disc; inside consisting of a pale or yellowish brown, loose and brittle central column consisting of pale brown t. prismatica and a lateral ring-like, dense, white to distinctly yellow fertile part with even or undulating margin, the latter also raising above the column, outside surrounded by a partly undulating, ca 20-25 µm thick black wall consisting of dark brown textura angularis of cells 4-10 µm in diameter at apical and upper peripheral regions, becoming paler downward and being absent at the base and lower sides. Interior of the fertile chambers consisting of isodiametric to elongate hyaline supporting cells and richly and irregularly branched hyphal conidiophores bearing phialides and conidia. Wall, supporting cells and phialides turning dilute violaceous in 3% KOH. Phialides arranged on supporting cells in palisades along the walls and on conidiophores, (6 –)8.2–12(– 15.3) × (1.7 –)2.5–3.5(– 5) µm (n = 80), repetitive, mostly lageniform, often with long necks; conidia also formed on cylindrical pegs and denticles. Conidia (6 –)6.7–8(– 8.8) × (2.5 –)3–3.5(– 3.7) µm, l/w (1.7 –)2.1–2.6(– 3.1) (n = 85), subfusiform, subclavate or ellipsoid, scar often distinct, smooth, with few minute drops.

Culture characteristics.

On CMD at 16 °C in the dark colony circular, dense, white, covered by white cottony aerial hyphae, partly turning pale apricot, reverse orange, not zonate.

Specimens examined

(all on recently detached twigs of Castanea sativa on ground). AUSTRIA, Burgenland, Forchtenstein, Kohlstatt, 13 Feb. 2016, H. Voglmayr (WU 37026); Steiermark, near highway A2 exit Steinberg, grid square 9057/1, 26 Oct. 2000, W. Jaklitsch W.J. 1651 (WU 37027); same locality, soc. Cytospora sp., 3 Nov. 2015, W. Jaklitsch & H. Voglmayr (WU 37028; culture CBS 145803 = D192). ITALY, Sicilia, Etna, above Zafferana Etnea, soc. Cytospora sp. ( Valsa morph), 17 June 2016, H. Voglmayr & W. Jaklitsch (WU 37029; culture D260); Veneto, Selva di Montello, 8 Apr. 2016, H. Voglmayr & W. Jaklitsch (WU 37030; culture D230).

Notes.

Sizes of pseudostromata and acervuli strongly depend on twig thickness. Remarkably, red colour of the ostiolar tip, when present, turns purple in 3% KOH and yellow in lactic acid, a feature, which is typical of the Hypocreales and within the Diaporthales otherwise only found in the Cryphonectriaceae .

So far, confirmed records of D. castaneum are only known from Europe where the species is widely co-occurring with its host, Castanea sativa . Kobayashi (1970) reported and illustrated D. castaneum (as Cryptodiaporthe castanea ) from Castanea crenata and C. mollissima in Japan. However, it is unlikely that these collections are conspecific with the European D. castaneum , considering their different spore shape and hosts. The 1 or 2 large guttules per ascospore cell and the ascospore appendages illustrated in Kobayashi (1970: fig. 32) are similar to D. atlanticum rather than to D. castaneum . Remarkably, he also reported and illustrated dimorphic conidia for the Japanese collections, which we also observed in D. atlanticum . Considering hosts and distribution, the Japanese collections likely represent one of the species described by Jiang et al. (2019) or an undescribed species.

Figures

Figure 5. Dendrostoma castaneum. Sexual morph a-d ectostromatic discs and ostioles (in a ostioles breaking through covering layer) e pseudostroma in vertical section f pseudostroma in cross section g peridium in section (in 3 % KOH) h-k asci l-s ascospores a, c-g, j, k, s WU 37030 = D 230 b, n-r WU 37026 h, i, l, m WU 37028 = D 192. Scale bars: 500 mm (a, c, d, f), 200 µm (b, e), 20 µm (g), 5 µm (h-s).

Figure 6. Dendrostoma castaneum (WU 37030 = D 230). Asexual morph a conidioma in face view b conidioma in cross section c, d conidiomata in vertical section e outer upper wall of fertile chamber f wall, short conidiophores and phialides (note violaceous tone) g, h phialides and hyphal conidiophores i-m conidia f-m In 3 % KOH. Scale bars: 300 µm (a-d), 10 µm (e-g), 5 µm (h, i), 3 µm (j-m).