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Species of Dendrostoma (Erythrogloeaceae, Diaporthales) associated with chestnut and oak canker diseases in China
expand article infoNing Jiang, Xin-Lei Fan, Pedro W. Crous§, Cheng-Ming Tian
‡ Beijing Forestry University, Beijing, China
§ Westerdijk Fungal Biodiversity Institute, Utrecht, Netherlands
Open Access

Abstract

Dendrostoma was recently proposed in Erythrogloeaceae (Diaporthales, Sordariomycetes), with all known members recorded as being plant pathogenic on economically important tree hosts. During our collections of Dendrostoma species in China, mild to severe canker symptoms were observed on sweet chestnut (Castanea mollissima) and oak (Quercus spp.) trees. Dead and dying plant tissues exhibiting Dendrostoma canker symptoms were sampled for fungal isolation. A total of 37 Dendrostoma isolates were obtained and analysed using morphological characteristics and molecular data (ITS, LSU, RPB2, TEF1-α). Based on these data, 10 novel clades could be distinguished, which also proved to represent morphologically distinct species described here as Dendrostoma aurorae, D. castaneae, D. castaneicola, D. chinense, D. dispersum, D. parasiticum, D. qinlingense, D. quercus, D. shaanxiense and D. shandongense spp. nov. A key to species of the genus is also provided.

Keywords

Canker, Castanea, multi-gene phylogeny, Quercus, systematics

Introduction

The family Erythrogloeaceae was established to accommodate Chrysocrypta, Disculoides, and Erythrogloeum, which exhibit epiphyllous acervuli along with subcylindrical to ampulliform conidiogenous cells and aseptate conidia (Senanayake et al. 2017). Erythrogloeum (Petrak 1953) is the type genus of Erythrogloeaceae and causes severe anthracnose on Hymenaea courbaril in South America (Ferreira et al. 1992). Chrysocrypta was first proposed in Cryphonectriaceae, being associated with leaf spots on Corymbia spp. in Australia (Crous et al. 2012a), but was subsequently transferred to Erythrogloeaceae, based on DNA sequence data (Senanayake et al. 2017). Disculoides was introduced with two initial species, D. eucalypti and D. eucalyptorum, discovered on diseased Eucalyptus leaves in Australia (Crous et al. 2012b). Two additional Disculoides species, D. calophyllae and D. corymbiae, were subsequently reported as foliar pathogens of Corymbia calophylla (Crous et al. 2016, 2017).

Dendrostoma (Erythrogloeaceae, Diaporthales) was recently introduced as a phytopathogenic fungal genus causing canker diseases on several economic hardwoods such as Malus spectabilis, Osmanthus fragrans and Quercus acutissima (Fan et al. 2018). Subsequently, Dendrostoma leiphaemia on Quercus trees was transferred from Amphiporthe based on ITS and LSU sequences analysis (Senanayake et al. 2018). Dendrostoma represents one of four genera in the family, but is the only one known to have a sexual morph. Hence, Erythrogloeaceae can be distinguished from the other diaporthalean families by multiguttulate and bicellular ascospores that are constricted at the septum and acervular conidiomata, with subcylindrical to ampulliform conidiogenous cells and hyaline to olivaceous, aseptate conidia (Rossman et al. 2007, Voglmayr and Jaklitsch 2014, Senanayake et al. 2017, Voglmayr et al. 2017, Fan et al. 2018).

The Erythrogloeaceae, including Chrysocrypta, Dendrostoma, Disculoides and Erythrogloeum, represent a family of fungal pathogens occurring on several commercially important tree genera such as Corymbia, Eucalyptus, Hymenaea, Malus, Osmanthus and Quercus in Australia, Brazil, China and Costa Rica (Petrak 1953, Ferreira et al. 1992, Crous et al. 2012a, b, 2016, 2017, Fan et al. 2018). Considering the importance of these tree diseases and the lack of taxonomic information on Dendrostoma, we conducted several surveys for members of the genus in China.

The aims of present study were (i) to describe the important Dendrostoma spp. associated with canker diseases on chestnut and oak trees in China and (ii) to provide a multi-gene phylogeny for the genus Dendrostoma based on a large set of freshly collected specimens in China. In agreement with previous taxonomic studies in Erythrogloeaceae, where different Disculoides spp. were discovered on Myrtaceae (Crous et al. 2012a, b, 2016, 2017), several Dendrostoma spp. were found on Fagaceae (Castanea and Quercus), being associated with mild to severe canker diseases. The Dendrostoma species were subsequently classified based on morphological characteristics and phylogenetic data.

Materials and methods

Sample collections and fungal isolates

Surveys for Dendrostoma species were conducted in plantations, nurseries, parks, gardens, on mountains and natural reserves in Beijing, Hebei, Shaanxi, Shandong, Tianjin and Zhejiang Provinces in China from 2017 to 2018. Typical canker symptoms were observed on stems, branches and twigs of different hosts, including Castanea mollissima, Quercus aliena, Q. aliena var. acuteserrata, Q. wutaishanica and other Quercus species (Fig. 1). Diseased samples were collected and placed in paper bags, then transferred to the laboratory for further study.

Figure 1. 

Chestnut plantations and Dendrostoma canker symptoms. A A chestnut plantation on the mountain B A chestnut plantation on the plain C Collection of the dead trees killed by Dendrostoma pathogens D–H Dendrostoma canker symptoms on host branches.

A total of 37 Dendrostoma isolates were established by removing a mucoid spore mass from sporulating ascomata and conidiomata produced on diseased bark, spreading the suspension on the surface of potato dextrose agar (PDA) plates and incubating the plates at 25 °C in the dark for up to 24 h. Single germinating spores were then transferred to clean plates under a dissecting microscope with a sterile needle. Specimens and isolates were deposited in the Museum of Beijing Forestry University (BJFC). Axenic cultures are maintained in the China Forestry Culture Collection Centre (CFCC).

Morphological analysis

The identification of Dendrostoma spp. was based on morphological features observed on the natural substrates. Cross-sections for ascomata and conidiomata from tree barks were prepared by hand using a double-edged blade under a dissecting microscope. At least 10 conidiomata/ascomata, 10 asci and 50 conidia/ascospores were measured to calculate the mean size and standard deviation. 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 is given in parentheses (Voglmayr et al. 2017). Microscopy photographs were captured with a Nikon Eclipse 80i compound microscope equipped with a Nikon digital sight DS-Ri2 high definition colour camera, using differential interference contrast illumination. Nomenclatural novelties and descriptions were deposited in MycoBank (Crous et al. 2004). Cultural characteristics were recorded for isolates incubated on PDA in the dark at 25 °C.

DNA extraction, PCR amplification and sequencing

Genomic DNA was extracted from fungal colonies growing on PDA using a modified cetyl trimethyl ammonium bromide method (CTAB; Doyle and Doyle 1990, Zhang et al. 2010). The ITS region was amplified using the primers ITS1 and ITS4 (White et al. 1990), the LSU region with the primers LR0R and LR5 (Vilgalys and Hester 1990), the RPB2 region with primers fRPB2-5F and fRPB2-7cR (Liu et al. 1999) and the partial TEF1-α gene with the primers EF1-728F and EF1-986R (Carbone and Kohn 1999). The PCR mixture for all regions consisted of 1 μl genomic DNA, 3 mM MgCl2, 20 μM of each dNTP, 0.2 μM of each primer and 0.25 U rTAQ DNA polymerase (TaKaRa, Shiga). Amplification of LSU and ITS were accomplished by an initial step of 2 min at 95 °C, followed by 35 cycles of 30 s at 95 °C, 30 s at 51 °C and 40 s at 72 °C, with a final extension of 10 min at 72 °C. For TEF1-α amplification, the 35 cycles consisted of initiation at 95 °C for 8 min, denaturation at 95 °C for 15 s, annealing at 55 °C for 20 s, elongation at 72 °C for 1 min and a final extension of 5 min at 72 °C. For RPB2, amplification of 35 cycles consisted of initiation at 95 °C for 5 min, denaturation at 95 °C for 30 s, annealing at 52 °C for 1 min, elongation at 72 °C for 1 min and a final extension of 10 min at 72 °C. The DNA sequencing was performed using an ABI PRISM 3730XL DNA Analyzer with BigDye Terminater Kit v. 3.1 (Invitrogen, Carlsbad) at the Shanghai Invitrogen Biological Technology Company Limited (Beijing).

Phylogenetic analyses

Sequences generated from the above primers of the different genomic regions (ITS, LSU, TEF1-α and RPB2) were analysed in comparison with those of Dendrostoma mali (CFCC 52102), D. leiphaemia (CBS 187.37), D. osmanthi (CFCC 52106, CFCC 52107, CFCC 52108 and CFCC 52109) and D. quercinum (CFCC 52103, CFCC 52104 and CFCC 52105) from Fan et al. (2018) and Senanayake et al. (2018). Corymbia corymbiae (CBS 132528), Disculoides eucalypti (CBS 132183) and D. eucalyptorum (CBS 132184) were selected as the outgroup taxa (Crous et al. 2012a, b). All sequences were aligned using MAFFT v. 6 (Katoh and Toh 2010) and edited manually using MEGA v. 6 (Tamura et al. 2013). Phylogenetic analyses were performed using PAUP v. 4.0b10 for maximum parsimony (MP) analysis (Swofford 2003) and PhyML v. 3.0 for Maximum Likelihood (ML) analysis (Guindon et al. 2010). The first analyses were performed on the combined multi-gene dataset (ITS, LSU, TEF1-α and RPB2) to compare isolates of Erythrogloeaceae species to ex-type sequence data from recent studies (Table 1).

Isolates and GenBank accession numbers used in the phylogenetic analyses.

Species Culture Location Host Host family GenBank accession numbers
ITS LSU TEF1−a RPB2
Chrysocrypta corymbiae CBS 132528* Australia Corymbia sp. Myrtaceae JX069867 JX069851 MH545457 MH545415
Dendrostoma aurorae CFCC 52753* China Castanea mollissima Fagaceae MH542498 MH542646 MH545447 MH545405
CFCC 52754 China Castanea mollissima Fagaceae MH542499 MH542647 MH545448 MH545406
Dendrostoma castaneae CFCC 52745* China Castanea mollissima Fagaceae MH542488 MH542644 MH545437 MH545395
CFCC 52746 China Castanea mollissima Fagaceae MH542489 NA MH545438 MH545396
CFCC 52747 China Castanea mollissima Fagaceae MH542490 NA MH545439 MH545397
CFCC 52748 China Castanea mollissima Fagaceae MH542491 NA MH545440 MH545398
CFCC 52749 China Castanea mollissima Fagaceae MH542492 MH542645 MH545441 MH545399
CFCC 52750 China Castanea mollissima Fagaceae MH542493 NA MH545442 MH545400
CFCC 52751 China Castanea mollissima Fagaceae MH542494 NA MH545443 MH545401
CFCC 52752 China Castanea mollissima Fagaceae MH542495 NA MH545444 MH545402
Dendrostoma castaneicola CFCC 52743* China Castanea mollissima Fagaceae MH542496 NA MH545445 MH545403
CFCC 52744 China Castanea mollissima Fagaceae MH542497 NA MH545446 MH545404
Dendrostoma chinense CFCC 52755* China Castanea mollissima Fagaceae MH542500 MH542648 MH545449 MH545407
CFCC 52756 China Castanea mollissima Fagaceae MH542501 MH542649 MH545450 MH545408
CFCC 52757 China Castanea mollissima Fagaceae MH542502 MH542650 MH545451 MH545409
CFCC 52758 China Castanea mollissima Fagaceae MH542503 MH542651 MH545452 MH545410
Dendrostoma dispersum CFCC 52730* China Quercus sp. Fagaceae MH542467 MH542629 MH545416 MH545374
CFCC 52731 China Quercus sp. Fagaceae MH542468 MH542630 MH545417 MH545375
Dendrostoma leiphaemia CBS 187.37 NA Quercus sp. Fagaceae MH855882 MH867393 NA NA
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 52108 China Osmanthus fragrans Oleaceae MG682074 MG682014 MG682034 MG682054
CFCC 52107 China Osmanthus fragrans Oleaceae MG682075 MG682015 MG682035 MG682055
CFCC 52109 China Osmanthus fragrans Oleaceae MG682076 MG682016 MG682036 MG682056
Dendrostoma parasiticum CFCC 52761 China Castanea mollissima Fagaceae MH542480 MH542636 MH545429 MH545387
CFCC 52763 China Castanea mollissima Fagaceae MH542481 MH542637 MH545430 MH545388
CFCC 52762* China Quercus wutaishanica Fagaceae MH542482 MH542638 MH545431 MH545389
CFCC 52764 China Quercus aliena Fagaceae MH542483 MH542639 MH545432 MH545390
CFCC 52765 China Castanea mollissima Fagaceae MH542484 MH542640 MH545433 MH545391
CFCC 52766 China Quercus aliena var. acuteserrata Fagaceae MH542485 MH542641 MH545434 MH545392
Dendrostoma qinlingense CFCC 52732* China Quercus wutaishanica Fagaceae MH542471 MH542633 MH545420 MH545378
CFCC 52733 China Quercus aliena var. acuteserrata Fagaceae MH542472 MH542634 MH545421 MH545379
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 NA MH545422 MH545380
CFCC 52735 China Quercus sp. Fagaceae MH542474 NA MH545423 MH545381
CFCC 52737 China Quercus sp. Fagaceae MH542475 NA MH545424 MH545382
CFCC 52739* China Quercus sp. Fagaceae MH542476 MH542635 MH545425 MH545383
CFCC 52738 China Quercus sp. Fagaceae MH542477 NA MH545426 MH545384
CFCC 52736 China Quercus sp. Fagaceae MH542478 NA MH545427 MH545385
CFCC 52740 China Quercus sp. Fagaceae MH542479 NA MH545428 MH545386
Dendrostoma shaanxiense CFCC 52741* China Castanea mollissima Fagaceae MH542486 MH542642 MH545435 MH545393
CFCC 52742 China Castanea mollissima Fagaceae MH542487 MH542643 MH545436 MH545394
Dendrostoma shandongense CFCC 52759* China Castanea mollissima Fagaceae MH542504 MH542652 MH545453 MH545411
CFCC 52760 China Castanea mollissima Fagaceae MH542505 MH542653 MH545454 MH545412
Disculoides eucalypti CBS 132183* Australia Eucalyptus sp. Myrtaceae JQ685517 JQ685523 MH545455 MH545413
Disculoides eucalyptorum CBS 132184* Australia Eucalyptus viminalis Myrtaceae JQ685518 JQ685524 MH545456 MH545414

A partition homogeneity test with heuristic search and 1000 replicates was performed using PAUP v. 4.0b10 to assess the discrepancy amongst the ITS, LSU, TEF1-α and RPB2 sequence datasets in reconstructing phylogenetic trees. MP analysis was run using a heuristic search option of 1000 search replicates with random-additions of sequences with a tree bisection and reconnection algorithm. Maxtrees were set to 5000, branches of zero length were collapsed and all equally parsimonious trees were saved. Other calculated parsimony scores were tree length (TL), consistency index (CI), retention index (RI) and rescaled consistency (RC). ML analysis was performed using a GTR site substitution model including a gamma-distributed rate heterogeneity and a proportion of invariant sites (Guindon et al. 2010). The branch support was evaluated using a bootstrapping method of 1000 replicates (Hillis and Bull 1993). Phylograms were shown using FigTree v. 1.3.1 (Rambaut and Drummond 2010). Novel sequences generated in the current study were deposited in GenBank (Table 1) and the aligned matrices used for phylogenetic analyses in TreeBASE (accession number: S22929).

Results

Phylogenetic analyses

The alignment based on the combined sequence dataset (ITS, LSU, TEF1-α and RPB2) included 46 ingroup taxa and three outgroup taxa, comprising 3536 characters in the aligned matrix. Of these, 2612 characters were constant, 175 variable characters were parsimony-uninformative and 749 characters were parsimony informative (101 from ITS, 21 from LSU, 389 from TEF1-α and 238 from RPB2). The MP analysis resulted in 108 equally most parsimonious trees (TL = 1590, CI = 0.744, RI = 0.897, RC = 0.668); the first tree is shown in Fig. 2. The phylogram based on the four gene sequences indicated 10 new species in Dendrostoma (Fig. 2), as described below.

Figure 2. 

Phylogenetic tree based on an MP analysis of a combined DNA dataset of ITS, LSU, TEF1-α and RPB2 gene sequences for the species of Dendrostoma. Bootstrap values ≥ 50% for MP and ML analyses are presented at the branches. Isolates representing ex-type material are marked with *.

Taxonomy

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

Type species

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

Description

Sexual morph: Pseudostromata small to large, distinct, circular, erumpent, consisting of an inconspicuous ectostromatic disc, semi-immersed to superficial, causing a pustulate bark surface. Ectostromatic disc flat or concave, orange, surrounded by bark flaps. Central column beneath the disc more or less conical. Stromatic zones lacking. Ascomata perithecial, conspicuous, umber to fuscous black, embedded in orange to umber pseudostromatic tissue, regularly scattered, surrounding the ectostromatic disc, with small to long ostioles that emerge within the ectostromatic disc. Ostioles flat in the disc or sometimes slightly projecting, cylindrical, sometimes obscuring the disc, covered by an orange, umber to fuscous black crust. Paraphyses deliquescent. Asci fusoid, 8-spored, 2–3-seriate, with an apical ring, becoming detached from the perithecial wall. Ascospores hyaline, fusoid to cylindrical, symmetrical to asymmetrical, straight to curved, bicellular, with a median septum, constricted at the septum, smooth, multiguttulate. Asexual morph: Conidiomata pycnidial, spherical to conical to pulvinate, occurring separately, immersed to semi-immersed in bark; wall of several layers of yellow textura angularis. Central column beneath the disc conical or not. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of cavity, hyaline, smooth, subcylindrical to ampulliform. Conidia hyaline, aseptate, smooth, multiguttulate or not, thin-walled, ellipsoid to fusoid, straight to curved.

Dendrostoma aurorae C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826795
Figure 3

Diagnosis

Dendrostoma aurorae differs from D. chinensis and D. shandongense by the existence of obvious central column.

Holotype

CHINA. Shaanxi Province: Lan’gao County, chestnut plantation, 32°13'43"N, 109°00'44"E, 1820 m a.s.l., on branches of Castanea mollissima, 3 Jul. 2017, N. Jiang (holotype: BJFC-S1561; ex-type culture: CFCC 52753).

Etymology

Aurorae, referring to the orange conidiomata with exuding conidial tendrils.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to pulvinate, occurring separately, bright yellow to orange, semi-immersed in bark, 300–500 μm high, 800–1400 μm diam.; wall of several layers of bright yellow textura angularis; conidiomata exuding slimy orange masses of conidia; central column beneath the disc more or less conical, pale yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 4–15 × 2.5–4 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, ellipsoid to fusoid, straight to curved, (7.2–)8.1–9.8(–10.3) × (2.1–)2.3–2.6(–2.8) μm, l/w = (2.7–)3.2–4.1(–4.2) (n = 50).

Figure 3. 

Morphology of Dendrostoma aurorae from Castanea mollissima (BJFC-S1561). A–C Habit of conidiomata on branches D Transverse section of conidioma E Longitudinal section through conidioma F, H Conidia G Conidiogenous cells. Scale bars: 1 mm (A); 0.5 mm (B, C, E); 0.2 mm (D); 5 μm (F, H); 10 μm (G).

Culture characters

On PDA, cultures are initially white, becoming isabelline after 2 weeks. The colonies are flat with irregular edge; texture uniform within 1 month at 25 °C in the dark.

Additional specimen examined

CHINA. Shaanxi Province: Lan’gao County, chestnut plantation, 32°13'43"N, 109°00'44"E, 1820 m a.s.l., on branches of Castanea mollissima, 3 Jul. 2017, N. Jiang, living culture CFCC 52754 (BJFC-S1562).

Notes

Dendrostoma aurorae was discovered on stems of dying chestnut trees and appears morphologically similar to the chestnut blight pathogen, Cryphonectria parasitica. However, these two diaporthalean pathogens can be distinguished by the existence of a central column inside the conidiomata of Dendrostoma aurorae. In the genus Dendrostoma, D. aurorae differs from D. chinensis and D. shandongense by the existence of an obvious central column.

Dendrostoma castaneae C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826796
Figure 4

Diagnosis

Dendrostoma castaneae is distinguished from the phylogenetically closely related species D. castaneicola by its narrower conidia.

Holotype

CHINA. Hebei Province: Xinglong County, chestnut plantation, 40°21'44"N, 117°51'29"E, 256 m a.s.l., on branches of Castanea mollissima, 27 Apr. 2018, N. Jiang & C.M. Tian (holotype: BJFC-S1553; ex-type culture: CFCC 52745).

Etymology

Castaneae, referring to the host genus, Castanea.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, pulvinate, occurring separately, bright yellow to orange, immersed in bark, 400–600 μm high, 900–2200 μm diam.; wall of several layers of brown textura angularis; central column beneath the disc irregular, pale yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 3–10 × 2–3.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, ellipsoid, straight to curved, (9.3–)10.4–12.3(–13.3) × (2.1–)2.2–2.7(–2.9) μm, l/w = (3.4–)4.2–5.2(–5.9) (n = 50).

Figure 4. 

Morphology of Dendrostoma castaneae from Castanea mollissima (BJFC-S1553). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidia F Conidiogenous cells. Scale bars: 1 mm (A–D); 10 μm (E–G).

Culture characters

On PDA, cultures are initially white, exhibiting grey after 2 weeks. Colonies are flat with irregular edge; texture initially uniform, producing concentric circles with faint orange conidiomata distributed outside the rim within 1 month at 25 °C in the dark.

Additional specimens examined

CHINA. Hebei Province: Chengde City, Xinglong County, chestnut plantation, 40°21'44"N, 117°51'29"E, 256 m a.s.l., on branches of Castanea mollissima, 27 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52748 (BJFC-S1556); Hebei Province: Chengde City, Xinglong County, chestnut plantation, 40°21'44"N, 117°51'29"E, 256 m a.s.l., on branches of Castanea mollissima, 27 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52751 (BJFC-S1557); Hebei Province: Chengde City, Xinglong County, chestnut plantation, 40°21'44"N, 117°51'29"E, 256 m a.s.l., on branches of Castanea mollissima, 27 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52747 (BJFC-S1559); Hebei Province: Chengde City, chestnut plantation, 40°37'39"N, 118°27'22"E, 256 m a.s.l., on branches of Castanea mollissima, 28 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52750 (BJFC-S1558); Hebei Province: Chengde City, chestnut plantation, 40°37'39"N, 118°27'22"E, 256 m a.s.l., on branches of Castanea mollissima, 28 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52752 (BJFC-S1560); Tianjin City: Jizhou District, chestnut plantation, 40°06'33"N, 117°42'45"E, 185 m a.s.l., on branches of Castanea mollissima, 25 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52749 (BJFC-S1554); Tianjin City: Jizhou District, chestnut plantation, 40°06'33"N, 117°42'45"E, 185 m a.s.l., on branches of Castanea mollissima, 25 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52746 (BJFC-S1555).

Notes

Dendrostoma castaneae is the most common species in this genus occurring on the host Castanea mollissima in China and is associated with canker symptoms on stems and branches. As shown in Fig. 2, Dendrostoma castaneae is the closest relative of D. castaneicola; however, they can be distinguished by conidial width (2.2–2.7 μm in D. castaneae vs. 3.2–3.8 μm in D. castaneicola).

Dendrostoma castaneicola C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826797
Figure 5

Diagnosis

Dendrostoma castaneicola differs from the two phylogenetically closely related species, D. castaneae and D. shaanxiense, by its white central column.

Holotype

CHINA. Hebei Province: Chengde City, chestnut plantation, 40°24'32"N, 117°28'55"E, 262 m a.s.l., on branches of Castanea mollissima, 28 Apr. 2018, N. Jiang & C.M. Tian (holotype: BJFC-S1551; ex-type culture: CFCC 52743).

Etymology

Castaneicola, referring to the host genus, Castanea.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to pulvinate, occurring separately, reddish-orange, semi-immersed in bark, 300–550 μm high, 900–1600 μm diam.; wall of several layers of faint yellow textura angularis; central column beneath the disc more or less conical, white. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 5–14 × 2–3.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, ellipsoid to fusoid, straight, (9.3–)10.5–12.8(–13.8) × (3.1–)3.2–3.8(–4.1) μm, l/w = (2.3–)3–4(–4.4) (n = 50).

Figure 5. 

Morphology of Dendrostoma castaneicola from Castanea mollissima (BJFC-S1551). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidia F Conidiogenous cells. Scale bars: 1 mm (A); 0.5 mm (B–D); 5 μm (E, G); 10 μm (F).

Culture characters

On PDA, cultures are initially white, becoming black after 2 weeks. The colonies are flat with irregular edge; texture uniform, producing a circle with faint orange conidiomata distributed along the edge of the circle within 1 month at 25 °C in the dark.

Additional specimen examined

CHINA. Hebei Province: Chengde City, Xinglong County, chestnut plantation, 40°21'44"N, 117°51'29"E, 256 m a.s.l., on branches of Castanea mollissima, 27 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52744 (BJFC-S1552).

Notes

Dendrostoma castaneicola, D. castaneae and D. shaanxiense comprise three closely related pathogen species causing chestnut canker diseases in China, all three species occurring on Castanea mollissima. They differ with regard to conidiomatal characteristics, including conidial dimensions (Table 2) and the central column colour (pale yellow central column in D. castaneae vs. white in D. castaneicola vs. bright yellow in D. shaanxiense). Additionally, Dendrostoma shaanxiense was only discovered in the Shaanxi Province, whereas D. castaneae and D. castaneicola were both distributed in Hebei Province.

Conidial size of Dendrostoma species from natural host barks, species with * were measured from conidia produced in PDA.

Species Conidial length (μm) Conidial width (μm) Length/width ratio
Dendrostoma aurorae 8.1–9.8 2.3–2.6 3.2–4.1
Dendrostoma castaneae 10.4–12.3 2.2–2.7 4.2–5.2
Dendrostoma castaneicola 10.5–12.8 3.2–3.8 3–4
Dendrostoma chinense 7.7–9.1 3.4–3.7 2.2–2.6
Dendrostoma dispersum 11.1–12.2 2–2.3 4.9–5.9
Dendrostoma mali* 3.5–4.5 2–2.5 NA
Dendrostoma osmanthi* 7.5–10.5 2–2.5 NA
Dendrostoma parasiticum 9.3–11.7 2.8–3.3 3–3.9
Dendrostoma qinlingense 16–18 3.3–3.7 4.4–5.2
Dendrostoma quercinum* 10.5–14 2.5 NA
Dendrostoma quercus 13.3–16.1 3.5–4.2 3.3–4.4
Dendrostoma shaanxiense 9.5–11.1 2.5–3.1 3.3–4.2
Dendrostoma shandongense 8.1–8.8 3.8–4.3 1.9–2.3

Dendrostoma chinense C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826798
Figure 6

Diagnosis

Dendrostoma chinense differs from D. shandongense by the appearance of conidiomata and is again similar to D. shandongense in its conidial characteristics.

Holotype

CHINA. Shandong Province: Rizhao City, Donggang District, chestnut plantation, 35°42'28"N, 119°46'23"E, 452 m a.s.l., on branches of Castanea mollissima, 14 Apr. 2017, N. Jiang (holotype: BJFC-S1563; ex-type culture: CFCC 52755).

Etymology

Chinense, referring to the country, China.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, spherical, occurring separately, black, semi-immersed in bark, 250–450 μm high, 600–850 μm diam.; wall of several layers of white textura angularis. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, ampulliform, 7–14 × 1–2.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate or not, thin-walled, fusoid to ellipsoid, apex acutely rounded, base truncate, (6.9–)7.7–9.1(–9.7) × (3.3–)3.4–3.7(–3.9) μm, l/w = (1.9–)2.2–2.6(–2.7) (n = 50).

Figure 6. 

Morphology of Dendrostoma chinense from Castanea mollissima (BJFC-S1563). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidia F Conidiogenous cells. Scale bars: 1 mm (A); 0.5 mm (B–D); 10 μm (E–G).

Culture characters

On PDA, cultures are initially white, becoming olive green in the outer zone after 2 weeks. Colonies are flat with a regular edge; texture uniform within 1 month at 25 °C in the dark.

Additional specimens examined

CHINA. Shandong Province: Rizhao City, Donggang District, chestnut plantation, 35°42'28"N, 119°46'23"E, 452 m a.s.l., on branches of Castanea mollissima, 14 Apr. 2017, N. Jiang, living culture CFCC 52756 (BJFC-S1564); Hebei Province: Chengde City, chestnut plantation, 40°24'32"N, 117°28'55"E, 262 m a.s.l., on branches of Castanea mollissima, 29 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52757 (BJFC-S1565); Hebei Province: Chengde City, chestnut plantation, 40°24'32"N, 117°28'55"E, 262 m a.s.l., on branches of Castanea mollissima, 29 Apr. 2018, N. Jiang & C.M. Tian, living culture CFCC 52757 (BJFC-S1566).

Notes

Dendrostoma chinense and D. shandongense have been occasionally discovered on the same branches and share similar conidial shape and dimensions. However, the conidiomatal appearance of these two species is quite different (black conidiomata in Dendrostoma chinense vs. orange conidiomata in D. shandongense).

Dendrostoma dispersum C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826799
Figure 7

Diagnosis

Dendrostoma dispersum can be distinguished from the phylogenetically closely related D. mali and D. quercinum based on its conidial dimensions.

Holotype

CHINA. Shaanxi Province: Beijing City: Mentougou District, Xiaolongmen Forest Park, 39°55'52"N, 115°45'15"E, 1670 m a.s.l., on branches of Quercus sp., 15 Aug. 2017, N. Jiang & X.L. Fan (holotype: BJFC-S1537; ex-type culture: CFCC 52730).

Etymology

Dispersum, referring to the conidiomata scattered on the bark surface.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to spherical, occurring separately, bright yellow, semi-immersed in bark, 500–800 μm high, 900–1500 μm diam.; wall of several layers of bright yellow textura angularis; central column beneath the disc conical, bright yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 6–15 × 2.5–5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, ellipsoid to fusoid, straight to curved, (10.9–)11.1–12.2(–12.8) × (1.9–)2–2.3(–2.4) μm, l/w = (4.8–)4.9–5.9(–6.3) (n = 50).

Figure 7. 

Morphology of Dendrostoma dispersum from Quercus sp. (BJFC-S1537). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidiogenous cells F Conidia. Scale bars: 1 mm (A); 0.5 mm (B–D); 10 μm (E, F), 5 μm (G).

Culture characters

On PDA, cultures are initially white, becoming faint yellow after 2 weeks. The colonies are flat with regular edge; texture uniform, producing concentric circles within 1 month at 25 °C in the dark.

Additional specimen examined

CHINA. Beijing City: Yanqing District, Yudu Mountain, 40°53'48"N, 115°54'48"E, 840 m a.s.l., on branches of Quercus sp., 12 Mar. 2018, N. Jiang, X.L. Fan, Y.M. Liang & C.M. Tian, living culture CFCC 52731 (BJFC-S1538).

Notes

Dendrostoma dispersum is phylogenetically close to D. mali and D. quercinum (Fig. 2). Conidial dimensions of Dendrostoma mali and D. quercinum were described from PDA plates (Fan et al. 2018) and D. dispersum can be differentiated from D. mali by having much longer conidia (11.1–12.2 μm in D. dispersum vs. 3–4.5 μm in D. mali) and from D. quercinum by narrower conidia (2–2.3 μm in D. dispersum vs. 2.5–3 μm in D. quercinum).

Dendrostoma parasiticum C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826822
Figure 8

Diagnosis

Dendrostoma parasiticum is distinguished from D. quercus by its shorter and narrower conidia.

Holotype

CHINA. Shaanxi Province: Shangluo City, Zhashui County, Longtougou Village, 33°39'27"N, 109°07'15"E, 2504 m a.s.l., on branches of Quercus wutaishanica, 8 Jul. 2017, N. Jiang (holotype: BJFC-S1570; ex-type culture: CFCC 52762).

Etymology

Parasiticum, referring to the fungus causing canker diseases on different hosts.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to spherical, occurring separately, yellow, semi-immersed in bark, 350–600 μm high, 1000–1800 μm diam.; wall of several layers of bright yellow textura angularis; central column beneath the disc conical, bright yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 7–12 × 2–3.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, fusoid, straight, (9.2–)9.3–11.7(–13.6) × (2.7–)2.8–3.3(–3.6) μm, l/w = (2.7–)3–3.9(–4.2) (n = 50).

Figure 8. 

Morphology of Dendrostoma parasiticum from Quercus wutaishanica (BJFC-S1570). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidia F Conidiogenous cells. Scale bars: 2 mm (A); 1 mm (B); 0.5 mm (C, D); 10 μm (E–G).

Culture characters

On PDA, cultures are initially white, becoming dark orange after 2 weeks. The colonies are flat with irregular edge; texture uniform, producing concentric circles within 1 month at 25 °C in the dark.

Additional specimens examined

CHINA. Shaanxi Province: Shangluo City, Zhashui County, chestnut plantation, 33°39'27"N, 109°07'15"E, 2504 m a.s.l., on branches of Castanea mollissima, 8 Jul. 2017, N. Jiang, living culture CFCC 52762 (BJFC-S1569); Shaanxi Province: Ankang City, Xiangxidong Park, 32°40'32"N, 109°18'57"E, 2504 m a.s.l., on branches of Castanea mollissima, 29 Jun. 2017, N. Jiang, living culture CFCC 52763 (BJFC-S1571); Beijing City: Mentougou District, Xiaolongmen Forest Park, 39°17'25"N, 115°45'23"E, 452 m a.s.l., on branches of Castanea mollissima, 17 Aug. 2017, N. Jiang & X.L. Fan, living culture CFCC 52764 (BJFC-S1572); Beijing City: Yanqing District, Yudu Mountain, 40°53'48"N, 115°54'48"E, 840 m a.s.l., on branches of Quercus aliena, 12 Mar. 2017, N. Jiang, X.L. Fan, Y.M. Liang & C.M. Tian, living culture CFCC 52765 (BJFC-S1573); Hebei Province: Chengde City, chestnut plantation, 40°24'32"N, 117°28'55"E, 262 m a.s.l., on branches of Quercus aliena var. acutiserrata, 15 Oct. 2017, N. Jiang, living culture CFCC 52766 (BJFC-S1574).

Notes

Dendrostoma parasiticum constitutes a widely distributed species occurring on several Fagaceae tree species including Castanea mollissima, Quercus aliena, Q. aliena var. acuteserrata and Q. wutaishansea. Dendrostoma parasiticum appears to be associated with tree dieback, canker and even tree death, although its pathogenicity remains unproven. Dendrostoma parasiticum is close to D. quercus in the phylogram (Fig. 2), but differs from D. quercus with shorter (9.3–11.7 μm in D. parasiticum vs. 13.3–16.1 μm in D. quercus) and narrower (2.8–3.3 μm in D. parasiticum vs. 3.5–4.2 μm in D. quercus) conidia.

Dendrostoma qinlingense C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826823
Figure 9

Diagnosis

Dendrostoma qinlingense produces the largest conidia amongst known species of the genus.

Holotype

CHINA. Baoji City, Mei County, Taibai Mountain, 34°15'43"N, 107°88'42"E, 2752 m a.s.l., on branches of Quercus wutaishanica, 13 Jul. 2017, N. Jiang (holotype: BJFC-S1539; ex-type culture: CFCC 52732).

Etymology

Qinlingense, referring to the Qinling Mountain.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to pulvinate, occurring separately, dark yellow, semi-immersed in bark, 400–700 μm high, 1100–1600 μm diam.; wall of several layers of bright yellow textura angularis; central column beneath the disc conical, dark orange. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, ampulliform, 6–22 × 2–3.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, fusoid, straight, (15.6–)16–18(–18.6) × (3.1–)3.3–3.7(–3.8) μm, l/w = (4.2–)4.4–5.2(–5.8) (n = 50).

Figure 9. 

Morphology of Dendrostoma qinlingense from Quercus wutaishanica (BJFC-S1539). A, B Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidiogenous cells F Conidia. Scale bars: 1 mm (A); 0.5 mm (B–D); 10 μm (E–G).

Culture characters

On PDA, cultures are initially white, exhibiting light grey after 2 weeks. The colonies are flat with irregular edge; texture uniform, producing concentric circles with sparse conidiomata irregularly distributed on the centre of the plate within 1 month at 25 °C in the dark.

Additional specimen examined

CHINA. Shaanxi Province: Baoji City, Mei County, Taibai Mountain, 34°15'43"N, 107°88'42"E, 2752 m a.s.l., on branches of Quercus aliena var. acutiserrata, 13 Jul. 2017, N. Jiang, living culture CFCC 52733 (BJFC-S1540).

Notes

Dendrostoma qinlingense was discovered on two Quercus species on the Qinling Mountain in northwest China. This species is phylogenetically related to Dendrostoma osmanthi on Osmanthus fragrans. However, Dendrostoma qinlingense differs from D. osmanthi by much larger conidia (16–18 × 3.3–3.7 μm in D. qinlingense vs. 7.5–10 × 2–2.5 μm in D. osmanthi).

Dendrostoma quercus C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826824
Figure 10

Diagnosis

Dendrostoma quercus is recognised by the existence of dimorphic conidia, which is unique in the genus.

Holotype

CHINA. Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian (holotype: BJFC-S1547; ex-type culture: CFCC 52739).

Etymology

Quercus, referring to the host genus, Quercus.

Description

Sexual morph: Pseudostromata erumpent, consisting of an inconspicuous ectostromatic disc, semi-immersed to superficial, causing a pustulate bark surface, 1000–1500 µm diam. Ectostromatic disc flat or concave, pale brown to brown, sometimes concealed by ostioles, surrounded by bark flaps, 400–800 µm diam.; central column yellowish to brownish. Stromatic zones lacking. Perithecia conspicuous, umber to fuscous black, 350–500 µm diam. Ostioles 5–8 per disc, flat in the disc or sometimes slightly projecting, cylindrical, covered by an orange, umber to fuscous black crust, 60–80 µm diam. Paraphyses slightly deliquescent. Asci fusoid to slightly fusiform, 8-spored, ascospores regularly disposed, with an apical ring, 55–65 × 8–11 µm. Ascospores hyaline, fusoid to cylindrical, smooth, often containing one guttule per cell to multiguttulate, symmetrical to asymmetrical, straight curved, bicellular, (13.4–)13.8–15.6(–16.6) × (5.1–)5.3–5.8(–5.9) μm, l/w = (2.4–)2.5–2.8(–2.9) (n = 50). Asexual morph: Conidiomata pycnidial, conical, occurring separately, pale yellow, semi-immersed in bark, 700–1000 μm high, 700–950 μm diam.; wall of several layers of pale yellow textura angularis; central column beneath the disc conical, yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 4.5–9 × 2–4 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, dimorphic, type one (> 99%) ellipsoid to fusoid, straight to curved, (11–)13.3–16.1(–16.9) × (3.4–)3.5–4.2(–4.5) μm, l/w = (2.6–)3.3–4.4(–4.9) (n = 50); type two (< 1%) fusoid, apex acutely rounded, 13–16 × 4–6 μm.

Figure 10. 

Morphology of Dendrostoma quercus from Quercus sp. (BJFC-S1547). A–C Habit of psedostromata on branches D Transverse section of pseudostroma E, H Habit of conidiomata on branches F Transverse section of conidioma G Longitudinal section through conidioma I Conidiogenous cells producing dimorphic conidia J Secondary conidia K Asci and ascospores L Ascospores M Primary conidia. Scale bars: 1 mm (A, H); 0.5 mm (B–G); 10 μm (I, K–M); 5 μm (J).

Culture characters

On PDA, cultures are initially white, becoming dark grey after 2 weeks. The colonies are flat with irregular edge; texture uniform, producing concentric circles with sparse conidiomata irregularly distributed within 1 month at 25 °C in the dark.

Additional specimens examined

CHINA. Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52734 (BJFC-S1548); Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52735 (BJFC-S1541); Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52736 (BJFC-S1542); Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52737 (BJFC-S1543); Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52738 (BJFC-S1544); Hebei Province: Qinhuangdao City, Zu Mountain, 40°14'13"N, 119°43'28"E, 1125 m a.s.l., on branches of Quercus sp., 2 May 2018, N. Jiang & C.M. Tian, living culture CFCC 52740 (BJFC-S1545).

Notes

Dendrostoma quercus is associated with oak branch cankers and forms both sexual and asexual fruiting structures beneath cankered bark. Within the genus, D. quercus produces the second largest conidia, smaller only than those of D. qinlingense (Table 2). The presence of dimorphic conidia in Dendrostoma, however, is a feature unique to D. quercus.

Dendrostoma shaanxiense C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826825
Figure 11

Diagnosis

Dendrostoma shaanxiense is distinguished from the closely related species D. castaneae by smaller l/w ratio and from D. castaneicola by its narrower conidia.

Holotype

CHINA. Shaanxi Province: Ankang City, Xiangxidong Park, 32°40'32"N, 109°18'57"E, 1079 m a.s.l., on branches of Castanea mollissima, 1 Jul. 2017, N. Jiang (holotype: BJFC-S1549; ex-type culture: CFCC 52741).

Etymology

Shaanxiense, referring to the Shaanxi Province in China.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, conical to pulvinate, occurring separately, dark orange, semi-immersed in bark, 350–650 μm high, 1050–1400 μm diam.; wall of several layers of bright yellow textura angularis; central column beneath the disc conical, bright yellow. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of the cavity, hyaline, smooth, subcylindrical to ampulliform, 5–11 × 2.5–3.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, ellipsoid to fusoid, straight to curved, (8.6–)9.5–11.1(–11.7) × (2.3–)2.5–3.1(–3.4) μm, l/w = (2.8–)3.3–4.2(–4.9) (n = 50).

Figure 11. 

Morphology of Dendrostoma shaanxiense from Castanea mollissima (BJFC-S1549). A, B&nbsp;Habit of conidiomata on branches C Transverse section of conidioma D Longitudinal section through conidioma E, G Conidia F Conidiogenous cells. Scale bars: 1 mm (A); 0.5 mm (B–D); 10 μm (E–G).

Culture characters

On PDA, cultures are initially white, turning purple after 2 weeks on PDA. The colonies are flat with irregular edge; texture uniform, producing concentric circles within 1 month at 25 °C in the dark.

Additional specimen examined

Shaanxi Province: Ankang City, Xiangxidong Park, 32°40'32"N, 109°18'57"E, 1079 m a.s.l., on branches of Castanea mollissima, 1 Jul. 2017, N. Jiang, CFCC 52742 (BJFC-S1550).

Notes

Dendrostoma shaanxiense, D. castaneae and D. castaneicola are phylogenetically closely related species occurring on the same host, Castanea mollissima (Fig. 2). However, Dendrostoma shaanxiense has conidia with a smaller l/w ratio than D. castaneae (3.3–4.2 in D. shaanxiense vs. 4.2–5.2 in D. castaneae) and has narrower conidia than D. castaneicola (2.5–3.1 μm diam. in D. shaanxiense vs. 3.2–3.8 μm diam. in D. castaneicola).

Dendrostoma shandongense C.M. Tian & N. Jiang, sp. nov.

MycoBank No: MB826826
Figure 12

Diagnosis

Dendrostoma shandongense is distinguished from its closest relative D. chinensis by the colour of conidiomata.

Holotype

CHINA. Shandong Province: Rizhao City, Donggang District, chestnut plantation, 35°42'28"N, 119°46'23"E, 452 m a.s.l., on branches of Castanea mollissima, 14 Apr. 2017, N. Jiang (holotype: BJFC-S1567; ex-type culture: CFCC 52759).

Etymology

Shandongense, referring to the Shandong Province in China.

Description

Sexual morph not observed. Asexual morph: Conidiomata pycnidial, spherical, occurring separately, reddish-orange, semi-immersed in bark, 250–400 μm high, 450–650 μm diam.; wall of several layers of black textura angularis. Conidiophores reduced to conidiogenous cells. Conidiogenous cells lining the inner walls of cavity, hyaline, smooth, ampulliform, 6.5–13 × 1–2.5 μm. Conidia hyaline, aseptate, smooth, multiguttulate, thin-walled, fusoid to ellipsoid, apex acutely rounded, base truncate, (7.8–)8.1–8.8(–9) × (3.7–)3.8–4.3(–4.8) μm, l/w = (1.6–)1.9–2.3(–2.4) (n = 50).

Figure 12. 

Morphology of Dendrostoma shandongense from Castanea mollissima (BJFC-S1567). A–C Habit of conidiomata on branches D Transverse section of conidioma E Longitudinal section through conidioma F Conidiogenous cells G Conidia. Scale bars: 1 mm (A); 0.3 mm (B–D); 5 μm (F); 5 μm (G).

Culture characters

On PDA, cultures are white. The colonies are flat with irregular edge; texture uniform, producing sparse conidiomata irregularly distributed near the centre of the plate within 1 month at 25 °C in the dark.

Additional specimen examined

Shandong Province: Rizhao City, Donggang District, chestnut plantation, 35°42'28"N, 119°46'23"E, 452 m a.s.l., on branches of Castanea mollissima, 14 Apr. 2017, N. Jiang, CFCC 52760 (BJFC-S1568).

Notes

Dendrostoma shandongense and D. chinensis occasionally occur on the same branches. These species are best distinguished by the appearance of their conidiomata, which are black in Dendrostoma chinense and orange in D. shandongense.

Discussion

In this study, we reviewed the taxonomic circumscription of Dendrostoma using molecular and morphological data. This is the first study that presents a robust phylogeny using a number of Dendrostoma isolates from different geographic origins. The results revealed up to 14 species in Dendrostoma based on the observation of type specimens and ex-type cultures (D. leiphaemia was not observed), of which 10 species were shown to represent new species, namely D. aurorae, D. castaneae, D. castaneicola, D. chinense, D. dispersum, D. parasiticum, D. qinlingense, D. quercus, D. shaanxiense and D. shandongense.

The 13 type specimens in Dendrostoma (except D. leiphaemia) were examined to establish robust morphological characteristics amongst specific ranks. Amongst these, 3 species, Dendrostoma mali, D. osmanthi and D. quercinum, were discovered to only have a sexual morph on natural hosts; 9 species, D. aurorae, D. castaneae, D. castaneicola, D. chinense, D. dispersum, D. parasiticum, D. qinlingense, D. shaanxiense and D. shandongense, were observed with only an asexual morph and only one species, D. quercus, was represented by both asexual and sexual morphs. Hence, morphological differences amongst Dendrostoma species were mainly established based on conidiomata produced on diseased host tissues, including colours of conidiomata, culture characteristics (Fig. 13), existence or non-existence of a central column, conidial shape and dimensions.

Figure 13. 

Dendrostoma cultures on PDA after 1 month at 25 °C, A D. aurorae B D. castaneae C D. castaneicola D D. chinense E D. dispersum F–G D. osmanthi H D. parasiticum I D. qinlingense J D. quercus; K D. shaanxiense L D. shandongense.

Dendrostoma shandongense and D. chinense are similar in conidial shape and size, but differ markedly from the other species. Additionally, Dendrostoma shandongense and D. chinense comprise the only two species in the genus with conidiomata lacking a central column structure, although they differ considerably with regard to in conidiomatal appearance (Figs 6, 13). The remaining eight species differ by the existence of a central column inside the conidiomata and can be further distinguished by their conidial characteristics, namely length, width and l/w ratio. Additionally, a key to the 14 Dendrostoma species is provided below.

Key to Dentrostoma species

1 Asexual morphs with or without sexual morphs known from natural substrates 2
Only sexual morph known from natural substrates 11
2 Central column absent, length/width ratio of conidia < 3 3
Central column present, length/width ratio of conidia > 3 4
3 Conidiomata orange D. shandongense
Conidiomata black D. chinense
4 Conidia dimorphic D. quercus
Conidia monomorphic 5
5 Conidial length > 15 μm D. qinlingense
Conidial length < 15 μm 6
6 Conidial length/width ratio > 4.2 7
Conidial length/width ratio < 4.2 8
7 Conidial length/width ratio 4.2–5.2, conidial width 2.2–2.7 μm D. castaneae
Conidial length/width ratio 4.9–5.9, conidial width 2–2.3 μm D. dispersum
8 Central column white D. castaneicola
Central column bright yellow or pale yellow 9
9 Central column pale yellow D. aurorae
Central column bright yellow 10
10 Conidial width 2.8–3.3 μm, length/width ratio 3–3.9 D. parasiticum
Conidial width 2.5–3.1 μm, length/width ratio 3.3–4.2 D. shaanxiense
11 Ascospores width > 5 μm D. leiphaemia
Ascospores width < 5 μm 12
12 Ascospores length > 15 μm D. quercinum
Ascospores length < 15 μm 13
13 On Osmanthus, Ascospores 11.5–14.5 × 3.5–4 μm D. osmanthi
On Malus, Ascospores 12–14 × 3–4 μm D. mali

The genus Dendrostoma was initially proposed to include three presumed plant pathogens causing canker diseases on hardwood trees, namely D. mali on Malus spectabilis, D. osmanthi on Osmanthus fragrans and D. quercinum on Quercus acutissima (Fan et al. 2018). Consistent with the previous study, the newly described 10 species were all isolated from fruiting structures associated with typical canker symptoms on several hardwood tree species, namely Castanea mollissima and Quercus spp.

The tree genera Castanea and Quercus in Fagaceae contain numerous important and common tree species in China, including C. mollissima, C. crenata, C. henryi, C. seguinii, Q. acutissima, Q. aliena, Q. dentata, Q. mongolica and Q. wutaishanica (Flora of China website: http://frps.eflora.cn/). Castanea mollissima constitutes one the most important crop tree species widely cultivated in 26 provinces in China. However, many plantations and nurseries planting Chinese chestnut suffer from fungal diseases that cause high production losses (Jiang et al. 2018). In particular, chestnut blight caused by Cryphonectria parasitica represents the most serious fungal disease, reducing host vitality and potentially killing the host (Jiang et al. 2018, Rigling and Prospero 2018).

In the present study, seven Dendrostoma species were observed on the host Castanea mollissima including D. aurorae, D. castaneae, D. castaneicola, D. chinense, D. parasiticum, D. shaanxiense and D. shandongense, causing chestnut canker diseases, termed Dendrostoma canker herein. Dendrostoma canker constitutes a newly discovered disease that has been observed in chestnut plantations and nurseries. Species of Dendrostoma usually infect host branches and stems, with occasional infection of twigs. Maturation of the fruiting structures from June to July resulted in death of the infected branches. Notably, no sexual fruiting structures were discovered during our investigations on chestnut trees.

Accurate recognition and identification of plant diseases are essential as fungal pathogens are constantly evolving and traditional control methods are frequently insufficient for disease control. In comparison, in the present study, Dendrostoma canker is considered to be caused by up to eight different species of Dendrostoma. Further studies are, however, required to confirm their pathogenicity and fully resolve their ecology.

Acknowledgements

This study was financed by the National Natural Science Foundation of China (Project No.: 31670647). We thank Yingmei Liang [Museum of Beijing Forestry University (BJFC), Beijing Forestry University], Chungen Piao and Minwei Guo [China Forestry Culture Collection Center (CFCC), Chinese Academy of Forestry, Beijing] for the preservation of materials studied during this study.

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