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Research Article
Beta-tubulin and Actin gene phylogeny supports Phaeoacremonium ovale as a new species from freshwater habitats in China
expand article infoShi-Ke Huang‡§|, Rajesh Jeewon, Kevin D. Hyde‡, D. Jayarama Bhat#¤, Putarak Chomnunti‡, Ting-Chi Wen|
‡ Mae Fah Luang University, Chiang Rai, Thailand
§ Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, China
| Guizhou University, Guiyang, China
¶ University of Mauritius, Reduit, Mauritius
# Azad Housing Society, Goa Velha, India
¤ Formerly, Department of Botany, Goa University, Goa, India

Corresponding author: Ting-Chi Wen ( tingchiwen@yahoo.com )

Academic editor: Marc Stadler
© 2018 Shi-Ke Huang, Rajesh Jeewon, Kevin D. Hyde, D. Jayarama Bhat, Putarak Chomnunti, Ting-Chi Wen.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Huang S-K, Jeewon R, Hyde KD, Bhat DJ, Chomnunti P, Wen T-C (2018) Beta-tubulin and Actin gene phylogeny supports Phaeoacremonium ovale as a new species from freshwater habitats in China. MycoKeys 41: 1-15. https://doi.org/10.3897/mycokeys.41.27536
Open Access

Abstract

A new species of Phaeoacremonium, P. ovale (Togniniaceae), was isolated during a diversity study of freshwater fungi from Yunnan Province in China. Morphological and cultural studies of the fungus were carried out and its sexual and asexual morphs (holomorph) are introduced herein. This species is characterised by peculiar long-necked, semi-immersed ascomata with oval to ellipsoid ascospores and ellipsoid to ovoid conidia. Phylogenetic analyses of a combined TUB and ACT gene dataset revealed that strains of P. ovale constitute a strongly supported independent lineage and are related to P. griseo-olivaceum and P. africanum. The number of nucleotide differences, across the genes analysed, also supports establishment of P. ovale as a new species.

Keywords

1 new species, Togniniales , Sordariomycetes , Morphology, Phylogeny

Introduction

Lignicolous freshwater fungi are important in nutrient recycling (Hyde et al. 2016). A number of taxonomic studies have focused on the diversity of such fungi in the South East Asian region and these investigations have reported a number of novel species (e.g. Jeewon et al. 2003; Cabanela et al. 2007; Zhang et al. 2008; Luo et al. 2018). In this study, we report a new species of Phaeoacremonium isolated from decaying wood from a stream in Yunnan Province, China.

Phaeoacremonium (= Togninia), introduced by Crous et al. (1996), is typified by P. parasiticum and it belongs to Togniniaceae (Gramaje et al. 2015). Phaeoacremonium was reported to be the asexual morph of Togninia (Mostert et al. 2003, 2006a; Pascoe et al. 2004). Gramaje et al. (2015) proposed Phaeoacremonium over Togninia as the correct name based on common usage and this has been listed in Réblová et al. (2016) and followed in Wijayawardene et al. (2018). The species are basically characterised by black ascomata with a long neck and clavate to cylindrical asci with oval to ellipsoid, hyaline ascospores and straight or flexuous mononematous conidiophores with oval to reniform phialo-conidia (Marin-Felix et al. 2018; Spies et al. 2018).

Most species of Phaeoacremonium are plant or/and human pathogens and some have been recorded on arthropods or in soil (Groenewald et al. 2001; Guarro et al. 2003; Hemashettar et al. 2006; Mostert et al. 2006a; Damm et al. 2008; Gramaje et al. 2015) while others are causal agents of Petri disease and esca of grapevines (Pascoe et al. 2004; Rooney-Latham et al. 2005a; Mostert et al. 2006b). Phaeoacremonium species can also infect a wide range of woody hosts, such as cherry, apricot, olive and peach trees (Rumbos 1986; Di Marco et al. 2004; Kubátová et al. 2004). Recent studies have reported the importance of Phaeoacremonium species in causing brown wood streaking of Olea spp. and Prunus spp. (Mostert et al. 2006b; Damm et al. 2008; Gramaje et al. 2012; Nigro et al. 2013; Olmo et al. 2014; Carlucci et al. 2015). Rooney-Latham et al. (2004, 2005a, b) reported that, in the presence of water, spores in some Phaeoacremonium species are forcibly discharged from perithecia through the long neck and exit the ostiole to be dispersed by wind, rain or insects in order to colonise other substrates. Recently Hu et al. (2012) introduced a freshwater inhabiting species, Phaeoacremonium aquaticum (= Togninia aquatica).

Species of Togniniaceae have been reported to colonise substrates in different types of habitats and recent taxonomic studies have revealed additional new species (Gramaje et al. 2015). We have been studying fungi along a north-south gradient in the Asian region (Hyde et al. 2016) and, in this study, we report on two collections of Phaeoacremonium from China. The aim here is to characterise these two strains as one novel species based on morphology as well as to investigate their phylogenetic affinities with previously known Togniniaceae species based on partial TUB and ACT genes.

Materials and methods

Sample collection, morphological studies and isolation

Submerged dead wood was collected from Baoshan, Yunnan Province in China in October 2016, brought to the laboratory in zip lock plastic bags and treated in the laboratory following procedures detailed in Luo et al. (2018). Fruiting bodies were found growing on decaying wood in a sterile plastic box after two weeks of incubation and the fungus was subsequently isolated based on the method of Chomnunti et al. (2014). Specimens were examined by a Motic SMZ 168 stereomicroscope. Micromorphological characters were examined using a Nikon ECLIPSE 80i compound microscope and images were captured with a Canon EOS 600D digital camera. Identification of colours was based on Ridgway (1912). The Taro soft Image Framework programme version 0.9.0.7 was used for measurements. Single spores were isolated and grown on water agar (WA) and potato dextrose agar (PDA) media. Ascospores germinated on PDA within 1 week. The colonies were transferred to WA and PDA to promote sporulation (sporulation occurred after 30 days in PDA). The cultures were checked 2 to 3 times per week and all procedures were performed in a sterile environment and at room temperature. The morphological characters of the asexual morph were examined after sporulation. Specimens are deposited in the Kunming Institute of Botany, Academia Sinica (KUN) and duplicated in Mae Fah Luang University (MFLU) Herbarium, Chiang Rai, Thailand. Facesoffungi numbers (FoF) (http://www.facesoffungi.org/) were obtained as stated in Jayasiri et al. (2015) and Index Fungorum numbers (IF) (http://www.indexfungorum.org/names/IndexFungorumRegisterName.asp).

DNA extraction, PCR amplification and sequencing

Total genomic DNA was extracted from mycelium using a Trelief Plant Genomic DNA Kit following the instructions of the manufacturer. The genomic DNA was amplified by using polymerase chain reaction (PCR) in a 25 μl reaction mixture. Partial regions of the beta-tubulin (TUB) and Actin (ACT) gene were amplified using the primer pairs T1 (O’Donnell and Cigelnik 1997) and Bt2b (Glass and Donaldson 1995), ACT-513F and ACT-783R (Carbone and Kohn 1999), respectively. The internal transcribed spacers (ITS) regions of the rDNA (ITS1-5.8S-ITS2) were also amplified using primer pairs ITS5 and ITS4 (White et al. 1990) but no further analyses were done on these due to lack of sequence data. The PCR conditions for these regions were as follows: an initial denaturation at 94 °C for 3 min, followed by 35 cycles of denaturation at 94 °C for 30 sec, annealing at 51 °C (TUB) or 60 °C (ACT) or 55 °C (ITS) for 50 sec and extension at 72 °C for 1 min, with a final extension at 72 °C for 10 min. PCR products were then sequenced with the primers mentioned above by a commercial sequencing provider (Tsingke Company, Beijing, P.R. China).

Phylogenetic analysis

The quality of the amplified nucleotide sequences was checked and combined by SeqMan version 7.1.0 (44.1) and Finch TV version 1.4.0 (www.geospiza.com). Sequences used by Marin-Felix et al. (2018), Spies et al. (2018) and the closest matches for our strains were retrieved from the National Center for Biotechnology Information (NCBI) by nucleotide BLAST. Sequences were aligned in MAFFT v. 7.310 (http://mafft.cbrc.jp/alignment/server/index.html) (Katoh and Standley 2016) and manually corrected in Bioedit 7.0.9.0 (Hall 1999).

The phylogenetic analyses of combined gene regions (TUB and ACT) were performed using maximum-likelihood (ML) and Bayesian Inference (BI) methods. The best-fit model (GTR+G+I) was obtained using jModelTest 2.1.10 under the Akaike Information Criterion (AIC) calculations (Darriba et al. 2012). The ML analysis was enforced with RAxML-HPC v.8 on XSEDE (Stamatakis 2014; Miller et al. 2015) with 1000 rapid bootstrap replicates. Bayesian inference was implemented by MrBayes v. 3.0b4 (Ronquist and Huelsenbeck 2003). Four simultaneous Markov chains were run for 5,000,000 generations sampling one tree every 1000th generations and other criteria as outlined by Hongsanan et al. (2017). The temperature value was lowered to 0.15, burn-in was set to 0.25. Gaps were treated as missing data with no differential weighting of transitions against transversions and the partition homogeneity test was performed to assess whether datasets from different genes were congruent. Phylogenetic trees were viewed with FigTree v1.4.0 (http:// tree.bio.ed.ac.uk/software/figtree/) and processed by Adobe Illustrator CS5. Alignment and trees were deposited in TreeBASE (submission ID: 22810). The nucleotide sequence data of the new taxon have been deposited in GenBank (Table 1).

Table 1.
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Strains and GenBank accession numbers of the isolates used in this study. Isolates from this study are marked with asterisk (*) and the type strains are in bold.

Species Voucher/Culture GenBank accession number
TUB ACT
Phaeoacremonium africanum CBS 120863 EU128100 EU128142
Phaeoacremonium album CBS 142688 KY906885 KY906884
Phaeoacremonium alvesii CBS 110034 AY579301 AY579234
Phaeoacremonium alvesii CBS 729.97 AY579302 AY579235
Phaeoacremonium amstelodamense CBS 110627 AY579295 AY579228
Phaeoacremonium amygdalinum CBS 128570 JN191307 JN191303
Phaeoacremonium amygdalinum CBS H-20507 JN191305 JN191301
Phaeoacremonium amygdalinum CBS H-20508 JN191306 JN191302
Phaeoacremonium angustius CBS 114992 DQ173104 DQ173127
Phaeoacremonium angustius CBS 114991 DQ173103 DQ173126
Phaeoacremonium argentinense CBS 777.83 DQ173108 DQ173135
Phaeoacremonium armeniacum ICMP 17421 EU596526 EU595463
Phaeoacremonium aureum CBS 142691 KY906657 KY906656
Phaeoacremonium australiense CBS 113589 AY579296 AY579229
Phaeoacremonium australiense CBS 113592 AY579297 AY579230
Phaeoacremonium austroafricanum CBS 112949 DQ173099 DQ173122
Phaeoacremonium austroafricanum CBS 114994 DQ173102 DQ173125
Phaeoacremonium austroafricanum CBS 114993 DQ173101 DQ173124
Phaeoacremonium bibendum CBS 142694 KY906759 KY906758
Phaeoacremonium canadens e PARC327 KF764651 KF764499
Phaeoacremonium cf. mortoniae ICMP 18088 HM116767 HM116773
Phaeoacremonium cinereum CBS 123909 FJ517161 FJ517153
Phaeoacremonium cinereum CBS H-20215 FJ517160 FJ517152
Phaeoacremonium cinereum CBS H-20213 FJ517158 FJ517150
Phaeoacremonium croatiense CBS 123037 EU863482 EU863514
Phaeoacremonium fraxinopennsylvanicum CBS 101585 AF246809 DQ173137
Phaeoacremonium fraxinopennsylvanicum CBS 110212 DQ173109 DQ173136
Phaeoacremonium fuscum CBS 120856 EU128098 EU128141
Phaeoacremonium gamsii CBS 142712 KY906741 KY906740
Phaeoacremonium geminum CBS 142713 KY906649 KY906648
Phaeoacremonium globosum ICMP 16988 EU596525 EU595466
Phaeoacremonium globosum ICMP 17038 EU596521 EU595465
Phaeoacremonium globosum ICMP 16987 EU596527 EU595459
Phaeoacremonium griseo-olivaceum CBS 120857 EU128097 EU128139
Phaeoacremonium griseorubrum CBS 111657 AY579294 AY579227
Phaeoacremonium griseorubrum CBS 566.97 AF246801 AY579226
Phaeoacremonium hispanicum CBS 123910 FJ517164 FJ517156
Phaeoacremonium hungaricum CBS 123036 EU863483 EU863515
Phaeoacremonium inflatipes CBS 391.71 AF246805 AY579259
Phaeoacremonium inflatipes CBS 113273 AY579323 AY579260
Phaeoacremonium iranianum CBS 101357 DQ173097 DQ173120
Phaeoacremonium iranianum CBS 117114 DQ173098 DQ173121
Phaeoacremonium italicum CBS 137763 KJ534074 KJ534046
Phaeoacremonium italicum CBS 137764 KJ534075 KJ534047
Phaeoacremonium italicum CBS H-21638 KJ534076 KJ534048
Phaeoacremonium junior CBS 142697 KY906709 KY906708
Phaeoacremonium krajdenii CBS 110118 AY579324 AY579261
Phaeoacremonium krajdenii CBS 109479 AY579330 AY579267
Phaeoacremonium longicollarum CBS 142699 KY906689 KY906688
Phaeoacremonium luteum CBS 137497 KF823800 KF835406
Phaeoacremonium meliae CBS 142710 KY906825 KY906824
Phaeoacremonium minimum CBS 246.91 AF246811 AY735497
Phaeoacremonium minimum CBS 100397 AF246806 AY735498
Phaeoacremonium mortoniae CBS 211.97 AF246810
Phaeoacremonium nordesticola CMM4312 KY030807 KY030803
Phaeoacremonium novae-zealandiae CBS 110156 DQ173110 DQ173139
Phaeoacremonium novae-zealandiae CBS 110157 DQ173111 DQ173140
Phaeoacremonium occidentale ICMP 17037 EU596524 EU595460
Phaeoacremonium oleae CBS 142704 KY906937 KY906936
*Phaeoacremonium ovale KUMCC 17-0145 MH395327 MH395325
*Phaeoacremonium ovale KUMCC 18-0018 MH395328 MH395326
Phaeoacremonium pallidum CBS 120862 EU128103 EU128144
Phaeoacremonium parasiticum CBS 860.73 AF246803 AY579253
Phaeoacremonium parasiticum CBS 113585 AY579307 AY579241
Phaeoacremonium parasiticum CBS 514.82 AY579306 AY579240
Phaeoacremonium paululum CBS 142705 KY906881 KY906880
Phaeoacremonium pravum CBS 142686 KY084246 KY084248
Phaeoacremonium proliferatum CBS 142706 KY906903 KY906902
Phaeoacremonium prunicola CBS 120858 EU128095 EU128137
Phaeoacremonium prunicola CBS 120858 EU128096 EU128138
Phaeoacremonium pseudopanacis CPC 28694 KY173609 KY173569
Phaeoacremonium roseum PARC273 KF764658 KF764506
Phaeoacremonium rosicola CBS 142708 KY906831 KY906830
Phaeoacremonium rubrigenum CBS 498.94 AF246802 AY579238
Phaeoacremonium rubrigenum CBS 112046 AY579305 AY579239
Phaeoacremonium santali CBS 137498 KF823797 KF835403
Phaeoacremonium scolyti CBS 113597 AF246800 AY579224
Phaeoacremonium scolyti CBS 113593 AY579293 AY579225
Phaeoacremonium scolyti CBS 112585 AY579292 AY579223
Phaeoacremonium sicilianum CBS 123034 EU863488 EU863520
Phaeoacremonium sicilianum CBS 123035 EU863489 EU863521
Phaeoacremonium sp. KMU 8592 AB986584 AB986583
Phaeoacremonium spadicum CBS 142711 KY906839 KY906838
Phaeoacremonium sphinctrophorum CBS 337.90 DQ173113 DQ173142
Phaeoacremonium sphinctrophorum CBS 694.88 DQ173114 DQ173143
Phaeoacremonium subulatum CBS 113584 AY579298 AY579231
Phaeoacremonium subulatum CBS 113587 AY579299 AY579232
Phaeoacremonium tardicrescens CBS 110573 AY579300 AY579233
Phaeoacremonium tectonae MFLUCC 13-0707 KT285563 KT285555
Phaeoacremonium tectonae MFLUCC 14-1131 KT285570 KT285562
Phaeoacremonium theobromatis CBS 111586 DQ173106 DQ173132
Phaeoacremonium tuscanicum CBS 123033 EU863458 EU863490
Phaeoacremonium venezuelense CBS 651.85 AY579320 AY579256
Phaeoacremonium venezuelense CBS 110119 AY579318 AY579254
Phaeoacremonium venezuelense CBS 113595 AY579319 AY579255
Phaeoacremonium vibratile CBS 117115 DQ649063 DQ649064
Phaeoacremonium viticola CBS 113065 DQ173105 DQ173128
Phaeoacremonium viticola CBS 101737 AF246817 DQ173129
Pleurostomophora richardsiae CBS 270.33 AY579334 AY579271
Wuestneia molokaiensis CBS 114877 AY579335 AY579272

Abbreviations: CBS: CBS-KNAW Collections, Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands; CMM: Culture Collection of Phytopathogenic fungi “Prof. Maria Menezes”; CPC: Culture collection of Pedro Crous, housed at CBS; HKUCC: The University of Hong Kong Culture Collection; ICMP: The International Collection of Microorganisms from Plants; KMU: Kanazawa Medical University herbarium; MFLU: Mae Fah Luang University herbarium, MFLUCC: Mae Fah Luang University Culture Collection, Chiang Rai, Thailand; PARC: Pacific Agri-Food Research Centre.

Results

Phylogenetic analyses

The combined TUB and ACT sequence dataset comprised 98 strains of Phaeoacremonium. The tree was rooted with Pleurostoma richardsiae (CBS 270.33) and Wuestineaia molokaiensis (CBS 114877). The alignment comprised 947 total characters including gaps (TUB: 646bp; ACT: 301bp). ML and BI analyses yielded trees which were topologically congruent in terms of species groupings. RAxML analysis yielded a best scoring tree with a final optimisation likelihood value of -15310.399369 (Fig. 1). In the phylogenetic tree, two strains of Phaeoacremonium ovale forms a well-supported independent subclade (100%, ML/1.00, PP) and closely related to other Phaeoacremonium species in Clade I (83%, ML/0.99, PP).

Figure 1. 

Maximum likelihood phylogenetic tree generated from analysis of a combined TUB and ACT sequences dataset for 98 taxa of Togniniaceae. Pleurostoma richardsiae (CBS 270.33) and Wuestineaia molokaiensis (CBS 114877) are the outgroup taxa. ML support values greater than 70% (BSML, left) and Bayesian posterior probabilities greater than 0.90 (BYPP, right) are indicated above the nodes. The strain numbers are noted after the species names. Ex-type strains are indicated in bold. Isolates from this study are indicated in red.

Taxonomy

Phaeoacremonium ovale S.K. Huang, R. Jeewon & K.D. Hyde, sp. nov.

Index Fungorum number: IF554786
Facesoffungi number: FoF 04685
Fig. 2

Type

CHINA, Yunnan Province, Baoshan, stream along the roadside; saprobic on dead wood, 21 December 2016; Huang S.K. (KUN HKAS99550, holotype; MFLU MFLU18-1076, isotype); ex-type living culture (KUMCC 17-0145; KUMCC 18-0018). GenBank no. (ITS: MH399732, TUB: MH395327, ACT: MH395325; ITS: MH399733, TUB: MH395328, ACT: MH395326)

Etymology

The name ovale refers to the oval shaped ascospores.

Description

Sexual morph: Ascomata 225–300 μm (n = 5), on wood, perithecial, solitary, semi-immersed, unilocular, subglobose to globose, black, ostiolate, with ostiolar neck erumpent through bark of host when mature. Neck 445–645 × 35–45 μm (x̄ = 530 × 40 μm, n = 5), centrally ostiolate, contorted, lined with hyaline periphyses. Peridium 17–40 μm diam., membranous, composed of dark brown to hyaline cells of textura angularis. Hamathecium composed of 2–6 μm wide, hyaline, septate paraphyses, slightly constricted at septa and gradually narrowed towards apex. Asci 11–20 × 3–6 μm (x̄ = 15.5 × 5 μm, n = 30), 8-spored, unitunicate, clavate, with short pedicel, apically rounded. Ascospores 3–5 × 1.5–3 μm (x̄ = 3.5 × 2 μm, n = 50), bi-seriate, hyaline, oval to ellipsoid, aseptate, smooth-walled, rounded at the ends. Asexual morph: Mycelium on culture, partly superficial, composed of septate, branched, hyaline, rarely verrucose, hyphae 1.5–3 μm diam., rarely with adelophialides. Conidiophores usually arising from hyaline hyphae, mononematous, unbranched, occasionally constricted at basal septum, hyaline. Phialides 8–15 × 2–4 μm (x̄ = 9.5 × 3 μm, n = 20), terminal, monophialidic, elongate-ampulliform and attenuated at base. Conidia 2.5–6 × 1–2.5 µm (x̄ = 4 × 2 μm, n = 30), hyaline, ellipsoid to ovoid, aseptate.

Figure 2. 

Phaeoacremonium ovale (HKAS99550, holotype). a Substrate b, c Ascoma on host d Squashed neck e Ascoma in vertical section fPeridiumg Asci surrounded by paraphyses h Asci i Septate paraphyses j–m Asci with ascospores n Germinating ascospores. Note: Fig. i stained in Congo red reagent, fig l stained in Melzer’s reagent. Scale bars: 500 µm (c); 200 µm (d); 100 µm (e); 50 µm (f, i); 30 µm (n); 20 µm (g–h); 10 µm (j–m)

Culture characteristics

Ascospore germinating on PDA within 1 week at 23°C, germ tubes produced from ends. Colonies growing on PDA, reaching 2 cm diam. and sporulating after 30 days. Colonies semi-immersed to superficial, irregular in shape, flat, slightly raised, with undulate edge, slightly rough on surface, cottony to fairly fluffy, colony from above, greyish-brown (5F3–5, Ridgway 1912) at the margin, initially write to cream (5A1–3) in the centre, becoming dark brown (5F7–8) at the margin, orange-white (5B1–3) at the centre; from below, initially, greyish-brown at the margin, white at the centre, becoming dark brown at the margin, orange-white at the centre, producing brown pigmentation in agar.

Discussion

Phaeoacremonium is currently accommodated in the monogeneric family Togniniaceae (Wijayawardene et al. 2018). To date, 65 species are accepted in this genus (Mostert et al. 2006b; Gramaje et al. 2015; Marin-Felix et al. 2018; Spies et al. 2018). While most of the species are commonly isolated as asexual morphs, some taxa have been recovered in their sexual morph state, viz. Phaeoacremonium aquaticum (= Togninia aquatica), P. viticola (= T. viticola), P. novae-zealandiae (= T. novae-zealandiae) (Hausner et al. 1992; Mostert et al. 2006a; Hu et al. 2012).

In this study, we introduce a novel taxon of Phaeoacremonium from dead wood collected in a stream in the Yunnan Province, China and describe its sexual and asexual morph. Examination of morphological characters reveal that our species is sufficiently distinct from extant species to establish it as a new species. Analyses of the combined DNA sequence dataset from partial TUB and ACT genes also support that this taxon is a Phaeoacremonium species and phylogenetically distinct from other species (Fig. 1). The two strains of P. ovale constitute a strongly supported independent lineage close to other species as depicted in Clade I. Phylogeny also reveals a close relationship to P. griseo-olivaceum, but with low support. To further support P. ovale as a new species, we compared nucleotide differences with other related species as recommended by Jeewon and Hyde (2016). Comparison of the 533 nucleotides across the TUB region reveals 43 bp (10%) differences, 256 bp of the ACT region reveals 22 bp (8.5%) differences and 517 bp of the ITS region reveals 4 bp (1%) differences compared to P. griseo-olivaceum (CBS 120857). Examination of the TUB region reveals 59 bp (11%) difference compared to P. africanum (CBS 120863) while the ACT region reveals 19 bp (7%) and ITS region reveals 17 bp (3%) differences, but the latter clusters in a different subclade in our phylogeny and is therefore considered distinct. There are also some morphological similarities between P. ovale and P. africanum in terms of black ascomata with a long neck, clavate asci and small, oval to ellipsoid ascospores in sexual morph and ellipsoid to ovoid, aseptate conidia in asexual morph (Damm et al. 2008). Despite a morphological resemblance to P. africanum and close relationship to P. griseo-olivaceum, there are other differences across these species. Phaeoacremonium ovale was collected from an aquatic habitat and from dead wood in China whereas the former two species were collected from Prunus spp. in South Africa (Damm et al. 2008). In addition, conidial size of P. africanum and P. griseo-olivaceum are 5–12 × 1.5–2 µm and 5–8 × 1.5–2 µm, whereas conidia of P. ovale measure 2.5–6 × 1–2.5 µm (Damm et al. 2008; Fig. 3). No sequence data of the TUB and ACT gene are available for P. aquaticum and P. leptorrhynchum and therefore we provide ITS sequences of our strains and compare them with those two species. Comparison of ITS regions reveals 61 bp (12%) differences with P. aquaticum (IFRDCC 3035) and 11 bp (2%) differences with P. leptorrhynchum (UAMH9590). In addition, our new species is also morphologically different from them. Phaeoacremonium ovale is morphologically different as ascospores of P. aquaticum and P. leptorrhynchum are reniform (ascospores of P. ovale are oval/ellipsoid) and measure 5–6 × 1–1.5 µm and 7–10 × 1–1.5 µm, respectively. Phaeoacremonium inconspicuum as described by Gramaje et al. (2015) also appears morphologically similar to P. ovale in terms of clavate asci and hyaline, aseptate ascospores (Eriksson and Yue 1990), but could not be included in our analyses as DNA sequences are unavailable. However, the ascospore shape and size of P. inconspicuum is different (allantoid, measuring 7–10 × 1.5–2 µm) (Eriksson and Yue 1990; Réblová 2011).

Figure 3. 

Phaeoacremonium ovale (HKAS99550, holotype). o Germinating ascospores, p 7 weeks of culture plate (above, left/reverse, right), q Mycelium with adelophialides r–t Branched conidiophores u–vConidia. Scale bars: 20 mm (p); 20 µm (o); 10 µm (r, t); 5 µm (q, s, u–v).

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 31760014), the Science and Technology Foundation of Guizhou Province (No. [2016]2863 & [2017]5788). Dr. Qi Zhao is acknowledged for his support and thanks to Dr. Sajeewa Maharachchikumbura for his valuable help in phylogenetic analyses. Shaun Pennycook is thanked for checking and correcting the Latin name.

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