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European species of Dendrostoma (Diaporthales)
expand article infoWalter M. Jaklitsch§, Hermann Voglmayr§
‡ University of Natural Resources and Life Sciences, Vienna, Austria
§ University of Vienna, Vienna, Austria
Open Access

Abstract

European species of the genus Dendrostoma (Erythrogloeaceae, Diaporthales) occurring on Castanea sativa and Quercus spp. based on freshly collected material are presented. Using a matrix of sequences from ITS, LSU, rpb2, and tef1, five species are recognized, and their phylogenetic positions are determined. Four species are added to the 14 described species of Dendrostoma. Dendrostoma atlanticum on Castanea sativa, D. creticum on Quercus coccifera and D. istriacum on Q. ilex are described as new species, Valsa castanea is combined in Dendrostoma, and D. leiphaemia is redescribed and illustrated. A key to the European species of Dendrostoma is provided.

Keywords

Amphiporthe, Cryptodiaporthe, multi-gene phylogeny, pyrenomycetes, systematics

Introduction

The genus Cryptodiaporthe, based on Cryptospora aesculi, is one of several segregates from the large genus Diaporthe (Diaporthales), characterized by the lack of stromatic zones and with asexual morphs recognized by Petrak (1921) as Septomyxa. In 1933, Wehmeyer (1933) recognized the relatively large number of species with a simple type of stroma development having various asexual morphs as a heterogeneous grouping. Petrak (1971) removed C. tiliae (as C. hranicensis) to his new genus Amphiporthe, mainly due to its Amphicytostroma asexual morph, where subsequently several species were added. Using the phylogenetic markers ITS, LSU, and rpb2, Mejía et al. (2008) detected that C. aesculi is congeneric with the generic type of Plagiostoma, P. euphorbiae. Thus, Cryptodiaporthe became a synonym of Plagiostoma. Subsequently (Mejía et al. 2011), several other species of Cryptodiaporthe were combined in Plagiostoma. Since the first phylogenetic treatment of the Diaporthales using DNA data (Castlebury et al. 2002), many old genera have been split and new ones described, and the proliferation of family names has forwarded a current number of 28, more than a half of which having been erected during the last three to four years (compare Jaklitsch et al. (2016), who listed 11 families). One of these families is the Erythrogloeaceae, whose members are based on phytopathogenic coelomycetous fungi (Chrysocrypta, Disculoides, Erythrogloeum). The only genus of this family for which sexual morphs are known is Dendrostoma (Fan et al. 2018). This genus is characterized by features common to many other diaporthalean genera forming pseudostromata lacking black stromatic margins, including Amphiporthe and Plagiostoma (Cryptodiaporthe). Rossman et al. (2015) already noted that Amphiporthe castanea and A. leiphaemia are not congeneric with A. tiliae (syn. A. hranicensis) and would need a new generic name. Amphiporthe leiphaemia was combined in Dendrostoma by Senanayake et al. (2018), based on ITS and LSU sequences of a CBS strain without giving any further information, whereas A. castanea has not been treated recently, although Jiang et al. (2019), who substantially enlarged the scope of the genus by describing 10 new species from Castanea and Quercus in China, recognized seven species on Castanea mollissima. Here we report on recently collected species of Dendrostoma occurring on Castanea sativa and Quercus spp. in Europe.

Materials and methods

Sample sources

All isolates included in this study originated from ascospores of freshly collected specimens derived from recently dead branches or twigs. Details of the strains including NCBI GenBank accession numbers of gene sequences used to compute the phylogenetic trees are listed in Table 1. Strain acronyms other than those of official culture collections are used here primarily as strain identifiers throughout the work. Representative isolates have been deposited at the Westerdijk Fungal Biodiversity Centre (CBS-KNAW), Utrecht, The Netherlands. Details of the specimens used for morphological investigations are listed in the Taxonomy section under the respective descriptions. Freshly collected specimens have been deposited in the Fungarium of the Department of Botany and Biodiversity Research, University of Vienna (WU).

Isolates and accession numbers of sequences used in the phylogenetic analyses.

Species Culture1,2 Country Host Host family GenBank accession numbers2
ITS LSU rpb2 tef1
Chrysocrypta corymbiae CBS 132528* Australia Corymbia sp. Myrtaceae JX069867 JX069851 MH545415 MH545457
Dendrostoma atlanticum D196 = CBS 145804* France Castanea sativa Fagaceae MN447223 MN447223 MN432160 MN432167
D303 Spain Castanea sativa Fagaceae MN447224 MN447224 MN432161 MN432168
Dendrostoma aurorae CFCC 52753* China Castanea mollissima Fagaceae MH542498 MH542646 MH545405 MH545447
CFCC 52754 China Castanea mollissima Fagaceae MH542499 MH542647 MH545406 MH545448
Dendrostoma castaneae CFCC 52745* China Castanea mollissima Fagaceae MH542488 MH542644 MH545395 MH545437
CFCC 52746 China Castanea mollissima Fagaceae MH542489 MH545396 MH545438
CFCC 52747 China Castanea mollissima Fagaceae MH542490 MH545397 MH545439
CFCC 52748 China Castanea mollissima Fagaceae MH542491 MH545398 MH545440
CFCC 52749 China Castanea mollissima Fagaceae MH542492 MH542645 MH545399 MH545441
CFCC 52750 China Castanea mollissima Fagaceae MH542493 MH545400 MH545442
CFCC 52751 China Castanea mollissima Fagaceae MH542494 MH545401 MH545443
CFCC 52752 China Castanea mollissima Fagaceae MH542495 MH545402 MH545444
Dendrostoma castaneicola CFCC 52743* China Castanea mollissima Fagaceae MH542496 MH545403 MH545445
CFCC 52744 China Castanea mollissima Fagaceae MH542497 MH545404 MH545446
Dendrostoma castaneum D192 = CBS 145803 Austria Castanea sativa Fagaceae MN447225 MN447225 MN432162 MN432169
D230 Italy Castanea sativa Fagaceae MN447226 MN447226 MN432170
D260 Italy Castanea sativa Fagaceae MN447227 MN447227
Dendrostoma chinense CFCC 52755* China Castanea mollissima Fagaceae MH542500 MH542648 MH545407 MH545449
CFCC 52756 China Castanea mollissima Fagaceae MH542501 MH542649 MH545408 MH545450
CFCC 52757 China Castanea mollissima Fagaceae MH542502 MH542650 MH545409 MH545451
CFCC 52758 China Castanea mollissima Fagaceae MH542503 MH542651 MH545410 MH545452
Dendrostoma creticum D124 = CBS 145802* Greece Quercus coccifera Fagaceae MN447228 MN447228 MN432163 MN432171
Dendrostoma dispersum CFCC 52730* China Quercus sp. Fagaceae MH542467 MH542629 MH545374 MH545416
CFCC 52731 China Quercus sp. Fagaceae MH542468 MH542630 MH545375 MH545417
Dendrostoma istriacum D122 = CBS 145801* Croatia Quercus ilex Fagaceae MN447229 MN447229 MN432164 MN432172
Dendrostoma leiphaemia D105 = CBS 145800 Austria Quercus robur Fagaceae MN447230 MN447230 MN432165 MN432173
D144 Poland Quercus robur Fagaceae MN447231 MN447231 MN432166 MN432174
CBS 187.37 NA Quercus sp. Fagaceae MH855882 MH867393
Dendrostoma mali CFCC 52102* China Malus spectabilis Rosaceae MG682072 MG682012 MG682032 MG682052
Dendrostoma osmanthi CFCC 52106* China Osmanthus fragrans Oleaceae MG682073 MG682013 MG682033 MG682053
CFCC 52107 China Osmanthus fragrans Oleaceae MG682075 MG682015 MG682035 MG682055
CFCC 52108 China Osmanthus fragrans Oleaceae MG682074 MG682014 MG682034 MG682054
CFCC 52109 China Osmanthus fragrans Oleaceae MG682076 MG682016 MG682036 MG682056
Dendrostoma parasiticum CFCC 52761 China Castanea mollissima Fagaceae MH542480 MH542636 MH545387 MH545429
CFCC 52762* China Quercus wutaishanica Fagaceae MH542482 MH542638 MH545389 MH545431
CFCC 52763 China Castanea mollissima Fagaceae MH542481 MH542637 MH545388 MH545430
CFCC 52764 China Quercus aliena Fagaceae MH542483 MH542639 MH545390 MH545432
CFCC 52765 China Castanea mollissima Fagaceae MH542484 MH542640 MH545391 MH545433
CFCC 52766 China Quercus aliena var. acutiserrata Fagaceae MH542485 MH542641 MH545392 MH545434
Dendrostoma qinlingense CFCC 52732* China Quercus wutaishanica Fagaceae MH542471 MH542633 MH545378 MH545420
CFCC 52733 China Quercus aliena var. acutiserrata Fagaceae MH542472 MH542634 MH545379 MH545421
Dendrostoma quercinum CFCC 52103* China Quercus acutissima Fagaceae MG682077 MG682017 MG682037 MG682057
CFCC 52104 China Quercus acutissima Fagaceae MG682078 MG682018 MG682038 MG682058
CFCC 52105 China Quercus acutissima Fagaceae MG682079 MG682019 MG682039 MG682059
Dendrostoma quercus CFCC 52734 China Quercus sp. Fagaceae MH542473 MH545380 MH545422
CFCC 52735 China Quercus sp. Fagaceae MH542474 MH545381 MH545423
CFCC 52736 China Quercus sp. Fagaceae MH542478 MH545385 MH545427
CFCC 52737 China Quercus sp. Fagaceae MH542475 MH545382 MH545424
CFCC 52738 China Quercus sp. Fagaceae MH542477 MH545384 MH545426
CFCC 52739* China Quercus sp. Fagaceae MH542476 MH542635 MH545383 MH545425
CFCC 52740 China Quercus sp. Fagaceae MH542479 MH545386 MH545428
Dendrostoma shaanxiense CFCC 52741* China Castanea mollissima Fagaceae MH542486 MH542642 MH545393 MH545435
CFCC 52742 China Castanea mollissima Fagaceae MH542487 MH542643 MH545394 MH545436
Dendrostoma shandongense CFCC 52759* China Castanea mollissima Fagaceae MH542504 MH542652 MH545411 MH545453
CFCC 52760 China Castanea mollissima Fagaceae MH542505 MH542653 MH545412 MH545454
Disculoides eucalypti CBS 132183* Australia Eucalyptus sp. Myrtaceae JQ685517 JQ685523 MH545413 MH545455
Disculoides eucalyptorum CBS 132184* Australia Eucalyptus viminalis Myrtaceae JQ685518 JQ685524 MH545414 MH545456

Morphology

Microscopic observations were made in tap water except where noted. Morphological analyses of microscopic characters were carried out as described by Jaklitsch (2009). Methods of microscopy included stereomicroscopy using a Nikon SMZ 1500 and Nomarski differential interference contrast (DIC) using the compound microscopes Nikon Eclipse E600 or Zeiss Axio Imager.A1 equipped with a Zeiss Axiocam 506 colour digital camera. Images and data were gathered using a Nikon Coolpix 4500 or a Nikon DS-U2 digital camera and measured by using the NIS-Elements D v. 3.0 or 3.22.15 or Zeiss ZEN Blue Edition software packages. For certain images of ascomata the stacking software Zerene Stacker v. 1.04 (Zerene Systems LLC, Richland, WA, USA) was used. Measurements are reported as maxima and minima in parentheses and the range representing the mean plus and minus the standard deviation of the number of measurements given in parentheses.

Culture preparation, DNA extraction, PCR, and sequencing

Ascospore isolates were prepared and grown on 2% corn meal dextrose agar (CMD; CMA: Sigma, St Louis, Missouri; supplemented with 2% (w/v) D(+)-glucosemonohydrate) or 2% malt extract agar (MEA; 2% w/v malt extract, 2% w/v agar-agar; Merck, Darmstadt, Germany). Cultures are illustrated in Figure 2. Growth of liquid cultures and extraction of genomic DNA was performed as reported previously (Voglmayr and Jaklitsch 2011; Jaklitsch et al. 2012) using the DNeasy Plant Mini Kit (QIAgen GmbH, Hilden, Germany). The following loci were amplified and sequenced: a ca 1.6 kb fragment containing the terminal part of the small subunit nuclear ribosomal DNA (nSSU rDNA), the complete internal transcribed spacer region (ITS1-5.8S-ITS2) and a ca 900 bp fragment of the large subunit nuclear ribosomal DNA (nLSU rDNA), amplified and sequenced as a single fragment with primers V9G (De Hoog and Gerrits van den Ende 1998) and LR5 (Vilgalys and Hester 1990); a ca 1.2 kb fragment of the RNA polymerase II subunit 2 (rpb2) gene with primers fRPB2-5f and fRPB2-7cr (Liu et al. 1999) or dRPB2-5f and dRPB2-7r (Voglmayr et al. 2016); a ca 1.3–1.5 kb fragment of the translation elongation factor 1-alpha (tef1) gene with primers EF1-728F (Carbone and Kohn 1999) and TEF1LLErev (Jaklitsch et al. 2005). PCR products were purified using an enzymatic PCR cleanup (Werle et al. 1994) as described in Voglmayr and Jaklitsch (2008). DNA was cycle-sequenced using the ABI PRISM Big Dye Terminator Cycle Sequencing Ready Reaction Kit v. 3.1 (Applied Biosystems, Warrington, UK) and the PCR primers; in addition, primers ITS4 (White et al. 1990), LR2R-A (Voglmayr et al. 2012), and LR3 (Vilgalys and Hester 1990) were used for the SSU-ITS-LSU region, and TEF1_INTF (forward, Jaklitsch 2009) and TEFD_iR1 (reverse, 5’ GAGTTYGAGGCYGGTATCTC 3’) or TEF1_INT2 (Voglmayr and Jaklitsch 2017) for tef1. Sequencing was performed on an automated DNA sequencer (3730xl Genetic Analyzer, Applied Biosystems).

Phylogenetic analyses

The newly generated sequences were aligned with the sequences of Jiang et al. (2019), and a combined matrix of the three loci (partial SSU-ITS-LSU rDNA, rpb2, and tef1) was produced for phylogenetic analyses, with three species (Chrysocrypta corymbiae, Disculoides eucalypti, and Disculoides eucalyptorum) added as the outgroup according to Jiang et al. (2019). The GenBank accession numbers of sequences used in the analyses are given in Table 1. Sequence alignments were produced with the server version of MAFFT (http://mafft.cbrc.jp/alignment/server/), checked and refined using BioEdit v. 7.2.6 (Hall 1999). The combined data matrix contained 4194 characters, viz. 1637 nucleotides of SSU-ITS-LSU, 1075 nucleotides of rpb2, and 1482 nucleotides of tef1.

Maximum parsimony (MP) analyses were performed with PAUP v. 4.0a165 (Swofford 2002). All molecular characters were unordered and given equal weight; analyses were performed with gaps treated as missing data; the COLLAPSE command was set to MINBRLEN. MP analysis of the combined multilocus matrix was done using 1000 replicates of heuristic search with random addition of sequences and subsequent TBR branch swapping (MULTREES option in effect, steepest descent option not in effect). Bootstrap analyses with 1000 replicates were performed in the same way but using 10 rounds of random sequence addition and subsequent branch swapping during each bootstrap replicate.

Maximum likelihood (ML) analyses were performed with RAxML (Stamatakis 2006) as implemented in raxmlGUI 1.3 (Silvestro and Michalak 2012), using the ML + rapid bootstrap setting and the GTRGAMMA substitution model with 1000 bootstrap replicates. The matrix was partitioned for the different gene regions. In the Results and Discussion, bootstrap values below 70% are considered low, between 70–90% medium, and above 90% high.

Results

Phylogenetic analyses

Of the 4194 characters included in the phylogenetic analyses, 703 were parsimony informative (133 from the SSU-ITS-LSU, 247 from rpb2, 323 from tef1). MP analyses revealed eight MP trees 1552 steps long, one of which is shown as Figure 1. The tree backbone was identical in all MP trees, except for the position of Dendrostoma castaneicola, which was embedded within D. castaneae in some of the MP trees (not shown). The best ML tree (lnL = −13985.7598) revealed by RAxML was compatible with the MP strict consensus tree, except for an interchanged position of D. atlanticum and D. shaanxiense (not shown). The genus Dendrostoma received maximum and medium support in the MP and ML analyses, respectively, and most of the tree backbone received significant support as well (Fig. 1). Although Dendrostoma accessions from Quercus and Castanea were interspersed, host-related patterns were obvious in the various Dendrostoma subclades (Fig. 1). The basal subclade A (D. castaneum, D. chinense, D. shandongense) contains only accessions from Castanea and is followed by subclade B (D. creticum, D. istriacum) from Quercus and subclade C with the single species D. aurorae from Castanea. Subclade D contains four species from Castanea (D. atlanticum, D. castaneae, D. castaneicola, D. shaanxiense) and subclade E three species from Quercus (D. dispersum, D. leiphaemia, D. quercinum) plus D. mali from Malus (Rosaceae). Finally, subclade F contains D. qinlingense and D. quercus from Quercus, D. parasiticum from Quercus and Castanea, and D. osmanthi from Osmanthus (Oleaceae). Geographically, no patterns were obvious, as the European accessions were distributed amongst the phylogenetic tree and embedded within lineages described from Eastern Asia (China).

Figure 1. 

Phylogram showing one of 8 MP trees 1552 steps long revealed by PAUP from an analysis of the combined ITS-LSU-rpb2-tef1 matrix of Dendrostoma, with Chrysocrypta corymbiae, Disculoides eucalypti and D. eucalyptorum added as outgroup taxa. MP and ML bootstrap support above 50% are given above or below the branches. The asterisk (*) denotes the node collapsed in the strict consensus of the eight MP trees. Accessions in bold were sequenced in the present study; accessions in blue were isolated from Castanea, those in green from Quercus, in orange from Malus and in red from Osmanthus.

Figure 2. 

Dendrostoma cultures (CMD, 16 °C) after 20d (e–h, m–p), 54–58 d (a–d, i–l). a–d D. atlanticum (a, b D192; c, d D230) e–h D. castaneum (a, b D196; c, d D303) i–j D. creticum D124 k–l D. istriacum D122 m–p D. leiphaemia (m, n D105; o, p D144) b, d, f, h, j, l, n, p reverse side.

Taxonomy

Dendrostoma X.L. Fan & C.M. Tian, Persoonia 40: 126 (2018)

Type species

Dendrostoma mali X.L. Fan & C.M. Tian.

Description, emended here

Sexual morph: pseudostromata immersed in bark and erumpent, causing a pustulate bark surface, consisting of an ectostromatic disc and entostroma with embedded ascomata. Ectostromatic disc flat or convex, surrounded by bark flaps. Entostroma light-coloured, prosenchymatous to nearly pseudoparenchymatous, mixed with bark cells, sometimes forming a more-or-less conical central column beneath the disc. Stromatic zones lacking or sometimes bark dorsally darkened. Ascomata perithecial, subglobose. Ostioles flat in the disc or slightly projecting, cylindrical, often with conical apical part. Paraphyses deliquescent. Asci oblong, fusoid, narrowly clavate or subellipsoid, with a refractive apical ring, containing (4–)6–8 ascospores in various arrangements, becoming detached at maturity. Ascospores hyaline, ellipsoid, fusoid, oblong to subacicular, often inequilateral, straight to curved, bicellular, more-or-less constricted at the median or eccentric septum, smooth, with 2–4 drops or multiguttulate, often with gelatinous terminal appendages. Asexual morph: conidiomata acervular, either forming lateral locules on the ostiolar level of sexual pseudostromata or separate, conical to pulvinate, immersed-erumpent from bark; wall pseudoparenchymatous. Often a pseudoparenchymatous conical central column present beneath the covering layer. Conidiophores non-differentiated, hypha-like or reduced to conidiogenous cells. Conidiogenous cells phialidic, lining the inner walls of cavities, subcylindrical to ampulliform, hyaline, shades of brown with age. Conidia hyaline, aseptate, smooth, multiguttulate or not, thin-walled, oblong, ellipsoid to fusoid, straight or curved.

Dendrostoma atlanticum Voglmayr & Jaklitsch, sp. nov.

MycoBank No: 832515
Figures 3, 4

Diagnosis

Dendrostoma atlanticum is recognized by clay-coloured ectostromatic discs and ascospores having large guttules and bristle-like appendages.

Holotype

France, Bretagne, Dépt. Morbihan (56), Saint Martin sur Oust, Beauvais, on twigs of Castanea sativa, soc. immature Valsaria sp., 15 Jan. 2016, A. Delannoy (WU 37024; ex-type culture CBS 145804 = D196).

Etymology

Atlanticum, referring to its occurrence in the Atlantic region.

Description

Sexual morph: pseudostromata 1–4.5 mm in their widest dimension in cross section, bluntly conical or pulvinate, circular, elliptic or irregular in outline, scattered, gregarious to confluent up to 7 mm length. Ectostromatic discs 0.4–2 mm in their widest dimension, distinct and conspicuous, projecting up to 0.5(–1) mm from the bark surface, pulvinate, circular, angular or fusoid in outline, with flat or convex top, initially whitish, turning pale to dark clay-coloured, splitting the periderm, often surrounded by bark flaps. Ostioles 1–40 per disc, often originating eccentrically from the perithecial venter, arranged in ring-like configuration or variably filling the disc, (44–)100–163(–195) µm (n = 42) in diameter at the tip, brown to black, cylindrical, sometimes attenuated towards tip, plane with the disc or projecting up to 300 µm; tip usually with dark umbilicate centre. Entostroma whitish, yellowish to pale bark coloured, consisting of thin-walled, hyaline to subhyaline 1–3 µm wide hyphae and bark cells. Perithecia (390–)480–660(–750) µm (n = 35) in diameter, depressed subglobose, collapsing upward upon drying; peridium ca 10–30 µm thick, colourless to pale olivaceous, consisting of hyaline to yellowish or pale brownish, thick-walled cells without clear contours, smaller and more-or-less isodiametric outside, larger and compressed inside, very variable, (3–)4–17(–38) in diameter (n = 66). Paraphyses of broad collapsing threads. Asci (64–)71–86(–90) × (11–)13–17(–19) µm (n = 35), fusoid to oblong, being released at maturity, containing 8 biseriate ascospores. Ascospores (13–)15–18(–20) × (4.3–)5.5–7(–8) µm, l/w (2.1–)2.4–2.9(–3.9) (n = 51), ellipsoid, often inequilateral, 2-celled, slightly constricted at the median septum, with the upper cell often slightly wider than the lower, hyaline, with 1–2 large and several small guttules per cell, smooth, with a hyaline, bristle-like, straight to curved appendage (10–)11.5–15.5(–21) × (1.5–)2–2.5(–2.8) µm (n = 101) at each end.

Asexual morph acervular. Conidiomata ca 1–2.2 mm in diameter, bluntly conical, width exceeding height, prosenchymatous. Covering discs 0.3–1.1 mm in diameter, flat to pulvinate, whitish cream to pale reddish brown. Central column whitish to reddish brown, usually darker toward the top; fertile chamber ring-like around the central column; walls and column consisting of pale yellowish brown textura angularis, outer wall and outer layer of the column containing numerous crystals. Phialides (3.7–)6.3–9.7(–11.5) × (2–)2.5–3.8(–4.7) µm (n = 46), arranged in a palisade on hyaline to yellowish, angular cells, ampulliform to lageniform, less commonly cylindrical. Conidia 1-celled, hyaline, smooth, dimorphic, both morphs formed in the same locule, either ellipsoid to oblong, (6.4–)7.7–10.2(–11.7) × (4–)4.5–5.7(–6) µm, l/w (1.4–)1.4–2.2(–3) (n = 21), with a large guttule and often distinct abscission scar, or cylindrical, (7.7–)10.2–13.5(–15.3) × (2.3–)2.5–3.2(–3.5) µm, l/w (2.8–)3.6–4.7(–5.6) (n = 45), straight or curved, with mostly 3 or 4 confluent guttules.

Culture characteristics

On CMD at 16 °C in the dark colony more-or-less circular, of loose mycelium, first white, variably covered by white aerial hyphae, becoming dense, forming white and apricot to orange zones, darkening and turning black from the centre, sometimes forming reddish brown dots, spots or tubercles.

Other specimen examined

Spain, Galicia, Pontevedra, O Grove, 42°28'04"N, 08°53'14"W, on twigs of Castanea sativa, 4 Nov. 2018, M.A. Delgado (WU 37025; culture D303).

Notes

Dendrostoma atlanticum is easily recognized by its long-pedicellate ascospores having 2–4 large drops, setting it apart from D. castaneum, which has narrow, often curved ascospores with small drops and short appendages. All species described from Castanea in China are only known from asexual morphs (Jiang et al. 2019).

Figure 3. 

Dendrostoma atlanticum. Sexual morph a–d ectostromatic discs and ostioles e pseudostroma in vertical section f pseudostroma in cross section g peridium in cross section (in 3% KOH) h–k asci l–r ascospores. a–c, f, h, i, k–p WU 37024 = D196), d, e, g, j, q, r WU 37025 = D303. Scale bars: 1 mm (f), 500 µm (a–e), 10 µm (g–r).

Figure 4. 

Dendrostoma atlanticum (WU 37024 = D196). Asexual morph a, b conidiomata in face view c conidioma in vertical section d vertical section through fertile chamber and part of the central column e, f phialides g–l conidia (cylindrical in g–j, ellipsoid in k, l). d–l In 3% KOH. Scale bars: 300 µm (a–c), 100 µm (d), 10 µm (e), 5 µm (f–l).

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

MycoBank No: 832516
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.

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 = D230 b, n–r WU 37026 h, i, l, m WU 37028 = D192. 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 = D230). 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).

Dendrostoma creticum Voglmayr & Jaklitsch, sp. nov.

MycoBank No: 832517
Figure 7

Diagnosis

Dendrostoma creticum is recognized by long, subacicular ascospores.

Holotype

Greece, Crete, near Askifou, 35°17'47"N, 24°12'33"E, on twigs of Quercus coccifera, soc. Cytospora (Valsa morph) sp., 6 June 2015, H. Voglmayr & W. Jaklitsch (WU 37031; ex-type culture CBS 145802 = D124)

Etymology

Creticum, referring to its occurrence, Crete.

Description

Sexual morph: pseudostromata 0.6–1.6 mm in their widest dimension in cross section, pulvinate, circular, elliptic or irregular in outline, scattered, gregarious to confluent up to 4 mm length, causing small bumps in the bark, splitting the periderm. Ectostromatic discs 0.25–1.4 mm in their widest dimension, medium to dark brown, flat or convex, surrounded by bark flaps. Ostioles 1–7 per disc, (31–)55–102(–135) µm (n = 40) in diameter at the rounded tip, dark brown to black, bluntly conical, plane with the disc or slightly prominent. Entostroma pale bark coloured, mottled. Perithecia (245–)320–445(–495) µm (n = 30) in diameter, depressed-subglobose, collapsing upward; peridium ca 10–50 µm thick, a dark brown textura angularis in face view, in section outside of dark brown textura angularis to strongly compressed cells (4–)7–14(–18) µm (n = 30) in diameter, inside of strongly compressed and elongated hyaline cells. Paraphyses absent at maturity. Asci (66–)71–85(–94) × (8.8–)9.5–11.2(–12.3) µm (n = 44), narrowly clavate to subfusoid, floating freely in the centre, containing 8 bi- to triseriate ascospores. Ascospores (26–)33–45.5(–52) × (2.7–)3–3.7(–4.6) µm, l/w (6.8–)9.8–14.3(–17.5) (n = 40), 2-celled, slightly constricted at the median or often distinctly eccentric septum, oblong, straight to curved, with the upper cell often slightly wider than the lower, hyaline, multiguttulate, smooth, with or without a hyaline subconical appendage (1.4–)1.5–2.3(–3.2) × (0.6–)0.9–1.3(–1.5) µm (n = 25) at each end.

Asexual morph unknown.

Culture characteristics

On CMD at 16 °C in the dark colony circular to irregular, dense, white, partly covered by short, white aerial hyphae, zonate, soon turning dark brown to black with pale apricot spots and margin and apricot to orange pigment diffusing into agar, reverse dark brown with orange margin.

Notes

Dendrostoma creticum is similar to the closely related D. istriacum but differs by distinctly longer ascospores, darker ectostromatic discs and a different host species.

Figure 7. 

Dendrostoma creticum (WU 37031 = D124). a, b, d Ectostromatic discs and ostioles in face view c pseudostroma in cross section e peridium in cross section in 3% KOH f–i asci j–r ascospores. Scale bars: 200 µm (a, b, d), 500 µm (c), 10 µm (e–r).

Dendrostoma istriacum Voglmayr & Jaklitsch, sp. nov.

MycoBank No: 832518
Figure 8

Diagnosis

Dendrostoma istriacum is recognized by narrow, oblong ascospores with small drops.

Holotype

CROATIA, Istria, Rovinj, near Kamp Amarin, 45°06'33"N, 13°37'02"E, on twigs of Quercus ilex, soc. Diplodia sp., 14 May 2015, H. Voglmayr (WU 37032; ex-type culture CBS 145801 = D122).

Etymology

Istriacum, referring to its occurrence, Istria.

Description

Sexual morph: pseudostromata 0.6–1.5 mm in their widest dimension in cross section, pulvinate, circular or elliptic in outline, scattered or tightly aggregated in large numbers, causing bumps in the bark and bark lesions to ca 3.2 mm long parallel to the twig axis. Ectostromatic discs 0.15–0.7 mm in diameter, mostly inconspicuous, surrounded by bark flaps, flat or convex, prosenchymatous, first whitish, turning pale to dark brown, becoming disintegrated and replaced by black ostioles and perithecial tops. Entostroma whitish to pale bark coloured. Stromatic tissues consisting of bark cells and 2–4 µm wide, hyaline to brown hyphae. Ostioles 1–5 per disc, (45–)61–91(–103) µm (n = 30) in diameter, short cylindrical, slightly projecting from the disc, brown to black; wall consisting of dark brown textura angularis. Perithecia (230–)280–393(–443) µm (n = 20) in diameter, globose to subglobose; peridium ca 15–35 µm thick, pale olivaceous to dark brown, consisting of 2–4 cell layers of thick-walled, dark brown angular cells (3–)4–13.5(–20.5) µm (n = 40) in diameter outside and long compressed, thin-walled, hyaline to brownish cells inside. Paraphyses absent at maturity. Asci (59–)62–70(–74) × (7–)8.5–10(–11) µm (n = 30), fusoid to narrowly clavate, floating freely in the centre, containing 8 bi- to triseriate ascospores. Ascospores (19.3–)20.5–25.5(–29.5) × (3–)3.5–4.2(–5.1) µm, l/w (4.5–)5.3–7(–8.7) (n = 40), 2-celled, constricted at the more-or-less median septum, oblong, straight to curved, with the upper cell often slightly wider than the lower, hyaline, containing several small guttules concentrated towards the ends and the septum, smooth, with a hyaline subconical appendage (1.7–)2.5–3.5(–4.5) × (0.8–)1–1.3(–1.5) µm (n = 40) at each end, becoming elongated in mounts.

Asexual morph: conidiomata ca 250–520 µm in diameter, acervular, inconspicuous, immersed in bark, causing small bark bumps, becoming visible in fissures, whitish to brownish, flat or convex, bluntly conical, usually broader than high, consisting of a broad sterile greyish brown central column, a white outer fertile ring and a brown covering layer; also fertile between the latter and the top of the column. Covering layer consisting of a dark brown textura angularis of 4–10 µm wide cells, turning paler to hyaline and more rounded downwards; column comprising pale brown textura angularis-epidermoidea of similarly sized cells; outer margin of the fertile ring consisting of a narrow layer of hyaline to pale brown, angular to compressed cells; gel surrounding rounded to angular, subhyaline to hyaline cells supporting phialides slowly turning pinkish in 3% KOH. Phialides forming palisades in fertile areas, tightly packed, cylindrical to ampulliform, often with long acute necks, (5.5–)6.3–9(–11) × (1.8–)2.2–3.7(–5.3) µm (n = 33). Conidia (4–)5–6.6(–7.4) × (1.9–)2.1–2.5(–2.7) µm, l/w (1.6–)2.1–3(–3.7) (n = 53), oblong to ellipsoid, 1-celled, hyaline, smooth, usually with distinct abscission scar.

Culture characteristics

On CMD at 16 °C in the dark, colony circular to irregular, dense, white, partly covered by short white aerial hyphae, zonate, soon turning dark brown to black with pale apricot to reddish brown spots and margin and some pale apricot pigment diffusing into agar, reverse dark brown with pale apricot margin.

Other specimen examined

CROATIA, Istria, Rovinj, near Kamp Veštar, 45°03'19"N, 13°40'55"E, on twigs of Quercus ilex, 30 May 2019, H. Voglmayr (WU 37033).

Notes

Dendrostoma istriacum is closely related to D. creticum but differs from that species by distinctly shorter ascospores and a different host species.

Figure 8. 

Dendrostoma istriacum (WU 37032 = D122). a–y Sexual morph a–c ectostromatic discs and ostioles d pseudostroma in cross section e peridium in cross section f–j, o–y ascospores k–n asci z–h1 asexual morph z conidioma in vertical section a1 upper part of conidioma showing covering layer, upper part of central column and fertile layers with opening at the upper right side b1 peripheral fertile chamber in vertical section c1 conidia attached to phialides d1–e1 phialides f1–h1 conidia; e, c1–h1 In 3% KOH. Scale bars: 150 µm (a–c, z), 300 µm (d), 100 µm (b1), 50 µm (a1), 10 µm (e–y, c1–e1), 5 µm (f1–h1).

Dendrostoma leiphaemia (Fr.: Fr.) Senan. & K.D. Hyde, in Senanayake et al., Fungal Diversity 93: 317 (2018).

Figure 9

Sphaeria leiphaemia Fr., Syst. mycol. (Lundae) 2(2): 399 (1823) (Basionym).

Amphiporthe leiphaemia (Fr.) Butin, Sydowia 33: 22 (1980).

Diaporthe leiphaemia (Fr. : Fr.) Sacc. [as ‘leiphaema’], Atti Soc. Veneto-Trent. Sci. Nat. 2(1): 135 (1873).

Valsa leiphaemia (Fr.) Fr., Summa veg. Scand., Sectio Post. (Stockholm): 412 (1849).

Diagnosis

Dendrostoma leiphaemia is recognized by conspicuous ectostromatic discs, broad conical ostiolar necks, and broad multiguttulate ascospores.

Description

Sexual morph: pseudostromata 1–5 mm in their widest dimension in cross section, pulvinate to conical, circular, elliptic or irregular in outline, scattered, aggregated to confluent, sometimes forming lines of up to 15 mm length, causing conspicuous bumps and lesions in the bark; dark brown dorsal zones present within the bark, absent in basal regions. Ectostromatic discs 0.35–2.5 mm in their widest dimension, conspicuous, whitish, cream, pale brown, pale yellowish brown to dull brown, fusoid, triangular to circular in section, flat or convex, often surrounded by bark flaps, elevated up to 1.3 mm beyond the bark surface, brittle to powdery, first present as a covering layer with ostiolar necks subsequently bursting through it, eventually crumbling away. Ostioles 1–30 per disc, (88–)124–220(–336) µm (n = 64) in diameter, dark brown, black, or reddish brown with black, rarely yellowish tip, cylindrical with conical apical part, attenuated to 35–90(–180) µm at the rounded, compressed or coarsely sulcate tip, projecting to 250, less commonly 400 µm, white, in upper regions sometimes yellow inside, periphysate, arising centrally to eccentrically from the perithecial venter and slightly convergent above perithecia; turning partly yellow, partly brown in 3% KOH. Entostroma whitish to pale yellowish or pale bark-coloured, prosenchymatous to pseudoparenchymatous, the latter particularly in the vicinity of perithecia, consisting of 1.5–5 µm wide hyphae or angular cells, mixed with bark cells. Perithecia arranged in valsoid configuration, tightly aggregated, (292–)380–625(–700) µm (n = 21) in diameter, globose to depressed-subglobose, with gelatinous contents, collapsing upward; peridium ca 7–35 µm thick, pale olivaceous to dark brown, consisting of an outer layer of isodiametric to elongate, thick-walled dark brown cells and an inner layer of compressed elongate, hyaline to brownish, thin-walled cells (5–)6.5–16(–22.5) µm (n = 31). Paraphyses absent at maturity. Asci floating freely in the centre when mature, (49–)58–71(–80) × (9–)10–13.5(–17.5) µm (n = 56), clavate, oblong, fusoid to subellipsoid, with a refractive apical ring, containing 8 bi- to triseriate, fasciculate or obliquely uniseriate ascospores. Ascospores (15–)16–19(–21) × (3.8–)4.3–5.2(–5.8) µm, l/w (2.7–)3.3–4.1(–4.7) (n = 95), 2-celled, not or slightly constricted at the median or slightly eccentric septum, inequilaterally ellipsoid or oblong, straight or curved, with the upper cell sometimes slightly wider than the lower, hyaline, multiguttulate, smooth, lacking appendages.

Asexual morph co-occurring with the sexual morph, acervular, either present as locules in lateral regions of pseudostromata above perithecia or forming separate, conical to pulvinate, dorsally blackened acervuli 0.9–2.2 mm in diameter, with conical upper part or whitish to cream or brownish, more-or-less circular, continous or deeply fissured discs ca 0.4–1 mm in diameter and whitish-cream, partly hollow interior containing slightly darker fertile chambers meandering through it. Walls and interior consisting of brown or hyaline to pale yellowish brown textura angularis. Phialides lining inner wall of the cavity, sessile, (4.8–)6.5–11(–12.7) × (1.7–)2–3.8(–5.3) µm (n = 16), subcylindrical to lageniform, reddish brown in 3% KOH (when old). Conidia (4.8–)7–9.5(–11) × (1.5–)1.8–2.3(–2.5) µm, l/w (2.3–)3.3–4.9(–6.3) (n = 50), unicellular, cylindrical, oblong, subclavate, rhomboid or narrowly ellipsoid, straight to slightly curved, often with a truncate or acute end, hyaline, turning pinkish-yellowish in 3% KOH, smooth, with minute terminal drops, adhering together in masses when old.

Culture characteristics

On CMD at 16 °C in the dark, colony irregular or dimorphic, dense, white, partly covered by short white aerial hyphae, zonate, soon turning dark brown to black with red or reddish brown spots, reverse dark brown, reddish brown with white, pale apricot or reddish brown spots and margins.

Specimens examined

AUSTRIA, Kärnten, St. Margareten im Rosental, shrubs in front of the Stariwald, grid square 9452/4, on branches of Quercus petraea, 9 Jan. 1995, W. Jaklitsch W.J. 443 (WU 37034); same area, 31 Dec. 1997, W. Jaklitsch W.J. 1122 (WU 37035); Niederösterreich, Hagenbrunn, Bisamberg east side, grid square 7664/3, on twigs of Quercus petraea, 30 Oct. 1999, W. Jaklitsch W.J. 1396 (WU 37036); Mannersdorf am Leithagebirge, on twigs of Quercus petraea, 12 Mar. 2016, H. Voglmayr (specimen lost); Mühlleiten, Herrnau, on branches of Quercus petraea, 29 Mar. 2015, H. Voglmayr (WU 37037; culture CBS 145800 = D105); Oberösterreich, Unterach am Attersee, Stockwinkl, Egelsee, grid square 8147/3, on branch of Quercus petraea, 25 May 1996, W. Jaklitsch W.J. 880 (WU 37038); Steiermark, Wundschuh, Kaiserwald, at the Seerestaurant, grid square 9058/4, on branch of Quercus petraea, 10 Sep. 2002, W. Jaklitsch W.J. 1936 (BPI 843342; culture A.R. 3874); Vienna, 19th district, at the Cobenzl, grid square 7763/2, on branches of Quercus cerris, 11 Feb 1995, W. Jaklitsch W.J. 482 (WU 37039); same area and host, 27 Feb. 1999, W. Jaklitsch W.J. 1286 (WU 37040). POLAND, E Grajewo, Kuligi, on branches of Quercus robur, 28 July 2015, H. Voglmayr (WU 37041; culture D144).

Notes

Asexual fructifications of this species are reported to have dimorphic conidia (Butin 1980; Wehmeyer 1933). However, for the description above only overmature material with a single type of conidia was available, the measurements of which agree with the cylindrical form given as 7–12 × 1.5–2 µm by Wehmeyer (1933), but their shape is more variable, possibly due to their age. As Butin (1980) observed, the asexual morph precedes the sexual morph and may still be present as separate acervuli among sexual pseudostromata or as locules within the periphery of the latter.

Figure 9. 

Dendrostoma leiphaemia. a–s Sexual morph a–e ectostromatic discs and ostioles f pseudostroma in cross section g pseudostroma in vertical section h peridium in cross section i, n–s ascospores j–m asci t–z asexual morph t conidioma in cross section u, v phialides w–z conidia; a, d–g, t–z WU 37037 (D105), b WU 37036 c, h, j, k, n WU 37038 i, l, m, p–s Mannersdorf o WU 37040. h, j, k, n, o, u–z In 3% KOH. Scale bars: 500 µm (a–g, t), 20 µm (h), 10 µm (j–m), 5 µm (i, n–s, u), 3 µm (v–z).

Key to European species of Dendrostoma

1 Ascospores without appendages, multiguttulate, 15–21 × 4–6 µm; on broad-leaved Quercus spp. D. leiphaemia
Ascospores with appendages 2
2 Appendages 10–21 µm long, bristle-like; ascospores with 1–2 large guttules per cell, 13–19.5 × 4.5–8 µm; on Castanea sativa D. atlanticum
Appendages <6 long, not bristle-like 3
3 Ascospores 11.5–20 × 3–5.3 µm, oblong, often curved, with 2 minute guttules per cell; on Castanea sativa D. castaneum
Ascospores longer 4
4 Ascospores oblong, 19–30 × 3–5 µm; on Quercus ilex D. istriacum
Ascospores oblong to subacicular, 26–52 × 2.7–4.5 µm; on Quercus coccifera D. creticum

Discussion

Our phylogenetic analyses are largely congruent with those of Jiang et al. (2019), and different topological positions of, e.g., D. aurorae and D. parasiticum concern backbone nodes with low to medium support. A notable difference concerns the position of the generic type, D. leiphaemia, which in Jiang et al. (2019) is contained within the D. osmanthiD. qinlingenseD. quercus clade with medium (80% MP) to high (90% ML) support, while in our analyses it is placed basal to the D. dispersumD. maliD. quercinum clade with medium support (76% MP, 88% ML). These differences may be due to different taxon and marker sampling, as in the analyses of Jiang et al. (2019) only the ITS and LSU rDNA were available for D. leiphaemia.

Previous authors recorded phytopathogenic potential in all species of Dendrostoma studied by them (Fan et al. 2018; Jiang et al. 2019). As an example, Dendrostoma castaneicola, D. castaneae, and D. shaanxiense were reported to cause chestnut canker (termed “Dendrostoma canker”) on Castanea mollissima in China (Jiang et al. 2019). It is remarkable that almost all Chinese Dendrostoma species recorded as canker pathogens by Jiang et al. (2019) were only found as asexual morphs, which were abundantly produced on the dead twigs. This may, at least partly, be linked to the fact that Jiang et al. (2019) mainly investigated chestnut plantations, in which asexual reproduction of virulent pathotypes may be particularly favoured by genetically uniform host cultivars. However, pathogenicity of these species has not been confirmed by inoculation experiments. Défago (1937) observed canker disease symptoms of Castanea sativa after artificial inoculation with Dendrostoma castaneum, and Kobayashi (1970) mentioned unpublished inoculation experiments showing pathogenicity of Dendrostoma sp. (as Cryptodiaporthe castanea) on cultivated Japanese chestnut varieties. Phillips and Burdekin (1982) considered D. castaneum to be a weak wound pathogen. In our studies, we have not seen any obvious disease symptoms exhibited by Castanea and Quercus species infected by species of Dendrostoma. The typical habitat of species like D. castaneum or D. leiphaemia are cut branches piled up on the ground. Species on evergreen Quercus spp. may occur on dead branchlets attached to trees, but their appearance is rather inconspicuous, and specific searches are necessary to spot them. However, as our observations have not been conducted to specifically study disease symptoms, it is premature to make predictions about potential pathogenicity, which thus cannot be excluded. Frequent association of Dendrostoma spp. with Cytospora spp. may suggest weak or facultative parasitism, but inoculation experiments are required to prove pathogenicity by fulfilling Koch’s postulates.

Although other genera of the Erythrogloeaceae produce acervuli, asexual morphs of Dendrostoma have been termed pycnidia (Fan et al. 2018; Jiang et al. 2019). This may be due to studies in culture, as asexual fructifications on agar may easily be interpreted as pycnidia, even when no true ostioles are present. However, none of the asexual morphs of the European species we have seen on natural substrates have preformed openings that may be termed ostioles. Therefore, we recognize asexual fructifications of Dendrostoma on natural substrates generally as acervuli. Jiang et al. (2019) found dimorphic conidia in a single species of Dendrostoma, D. quercus. Here we add another such species, D. atlanticum. These forms occur at the same time in the same asexual fructifications. However, to gain a complete picture of asexual morphs and elucidate entire life cycles of Dendrostoma species, long-term studies may be required, as certain asexual fungi have two different morphs, which may not occur at the same time (Butin 1980).

Most species of Dendrostoma are only known as asexual morphs. Only one of the 10 species described by Jiang et al. (2019), D. quercus, has a sexual morph. However, it is unclear whether in these species sexual morphs are absent, only rarely produced or have not yet been recorded, e.g., due to unfavourable weather conditions for development, unsuitable substrates or an untimely sampling season. Other species, for which sexual morphs are known are D. mali on Malus spectabilis, D. osmanthi on Osmanthus fragrans, and D. quercinum on Quercus acutissima (Fan et al. 2018). All five species of Dendrostoma we describe or redescribe from Europe, two from Castanea sativa and three from Quercus spp., have sexual morphs and in all but one (D. creticum) we found also an asexual morph on the natural hosts.

The high species biodiversity of Dendrostoma recorded from Eastern Asia as well as the phylogenetic patterns indicate that the group may have originated in this area. This is also supported by the fact that the European species do not form a monophyletic group, but are embedded within Eastern Asian lineages, indicating that Europe has been colonised from Asia several times independently. In addition, evolutionary radiation may have started on Castanea as the basal subclade A exclusively contains accessions from that host (Fig. 1). However, detailed additional studies including other areas as well as hosts are necessary to vigorously test these hypotheses.

Acknowledgments

We thank Alain Delannoy, Miguel Angel Delgado, and Joseba Castillo for providing fresh material of Dendrostoma atlanticum and Irmgard Greilhuber and Walter Till (WU) for incorporating the specimens in the herbarium. The financial support by the Austrian Science Fund (FWF; project P27645-B16) to HV is gratefully acknowledged.

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