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Research Article
Multi-gene phylogenetic evidence suggests Dictyoarthrinium belongs in Didymosphaeriaceae (Pleosporales, Dothideomycetes) and Dictyoarthrinium musae sp. nov. on Musa from Thailand
expand article infoBinu C. Samarakoon§, Dhanushka N. Wanasinghe|, Milan C. Samarakoon§, Rungtiwa Phookamsak|, Eric H.C. McKenzie#, Putarak Chomnunti§, Kevin D. Hyde¤§, Saisamorn Lumyong«, Samantha C. Karunarathna|
‡ Chiang Mai University, Chiang Mai, Thailand
§ Mae Fah Luang University, Chiang Rai, Thailand
| Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, China
¶ World Agro Forestry Centre, Kunming, China
# Manaaki Whenua-Landcare Research, Auckland, New Zealand
¤ Zhongkai University of Agriculture and Engineering, Guangzhou, China
« Academy of Science, The Royal Society of Thailand, Bangkok, Thailand
Open Access

Abstract

Dead leaves of Musa sp. (banana) were collected in northern Thailand during an investigation of saprobic fungi. Preliminary morphological observations revealed that three specimens belong to Dictyoarthrinium. Phylogenetic analyses of combined SSU, LSU, ITS and tef1-α sequence data revealed that Dictyoarthrinium forms a clade in Didymosphaeriaceae (Massarineae, Pleosporales, Dothideomycetes) sister to Spegazzinia. Based on contrasting morphological features with the extant taxa of Dictyoarthrinium, coupled with the multigene analyses, Dictyoarthrinium musae sp. nov. is introduced herein. Our study provides the first detailed molecular investigation for Dictyoarthrinium and supports its placement in Didymosphaeriaceae (Massarineae, Pleosporales, Dothideomycetes). Previously, Dictyoarthrinium was classified in Apiosporaceae (Xylariales, Sordariomycetes).

Keywords

Banana, Dictyoarthrinium sacchari, DNA sequences, Musaceae, one new species, saprobes, taxonomy

Introduction

Hughes (1953) documented seven hyphomycete genera (Arthrinium, Catenospegazzinia, Cordella, Dictyoarthrinium, Endocalyx, Pteroconium and Spegazzinia) that had unique basauxic conidiogenous cell development. Hyde et al. (1998) accommodated Dictyoarthrinium, Endocalyx, Scyphospora (= Arthrinium) and Spegazzinia in Apiosporaceae (Xylariales, Sordariomycetes), based on morphological characteristics. Based on molecular phylogenetic data (LSU and ITS), Cordella and Pteroconium were synonymised under Arthrinium by Crous and Groenewald (2013) and Arthrinium was confirmed as the asexual morph of Apiospora. With the availability of molecular data (SSU, LSU, ITS and tef1-α), Tanaka et al. (2015) transferred Spegazzinia to Didymosphaeriaceae. Wijayawardene et al. (2018) and Hyde et al. (2020) accommodated Arthrinium, Dictyoarthrinium and Endocalyx, all with basauxic conidiogenous cell development, in Apiosporaceae.

Dictyoarthrinium was introduced by Hughes (1952) with D. quadratum as the type species. Dictyoarthrinium africanum was simultaneously introduced. Damon (1953) re-examined the type material, descriptions and illustrations of Tetracoccosporium sacchari (Johnston and Stevenson 1917) and mentioned that T. sacchari was congeneric with Dictyoarthrinium quadratum. Therefore, Damon (1953) combined T. sacchari as Dictyoarthrinium sacchari. Damon (1953) also named D. quadratum as the heterotypic synonym of D. sacchari. Rao and Rao (1964) introduced D. lilliputeum and D. microsporum, while Kobayasi et al. (1971) introduced D. rabaulense as novel taxa to the genus. Somrithipol (2007) introduced D. synnematicum and currently seven epithets of Dictyoarthrinium are listed in Index Fungorum (2020). All Dictyoarthrinium species were introduced, based only on morphological data. Vu et al. (2019) sequenced D. sacchari (CBS 529.73) and submitted LSU data to GenBank as the only valid molecular record for the genus.

Dictyoarthrinium is characterised by basauxic conidiogenous cell development (Hughes 1952; Damon 1953; Matsushima 1971). Basauxic development is demonstrated by conidiogenous cells in which elongation occurs at a basal growing point after formation of a single, terminal blastic conidium at its apex (Cole 1976). Conidiophores of Dictyoarthrinium are minutely verruculose, subhyaline and transversely septate (Ellis 1971). Usually, the septa are dark brown and appear as thick stripes on the conidiophore. Conidiophore mother cells are often hyaline or pale brown and cup-shaped (Hughes 1952) or subspherical (Ellis 1971). The length of conidiophores varies within the genus, but in some species, the dimensions are more or less similar. Conidia of Dictyoarthrinium arise from the conidiophore at terminal or lateral parts. Conidiogenesis is monoblastic or polyblastic and integrated (Ellis 1971). Conidia are simple, solitary, dematiaceous and often four-celled. Some taxa (e.g. D. africanum) have 16-celled conidia (Hughes 1952). The surface of conidia is verruculose and most species have warts on the surface. However, the conidia of D. rabaulense are densely echinulate with long spines (Kobayasi 1971). The conidia vary in shape from square to spherical, subspherical or oblong. Most conidia appear flattened on one side. As a specific feature, only D. synnematicum possesses synnemata with filaments (Somrithipol 2007). Stroma, setae and hyphopodia have not been observed in Dictyoarthrinium.

Many Dictyoarthrinium species are saprobes that colonise dead plant materials, although D. rabaulense was recorded even from soil and air (Kobayasi et al. 1971; Ellis 1976). Most Dictyoarthrinium species occur on monocotyledonous plants. The genus is widely distributed across the tropics, mainly in terrestrial environments (Ellis 1971; 1976). The sexual morph of Dictyoarthrinium is unknown. Hosts, substrates and geographical distributions of extant Dictyoarthrinium species are listed in Table 1.

Table 1.

Hosts, substrates and geographical distribution of Dictyoarthrinium species.

Species Hosts/substrates Geographical distribution References
Dictyoarthrinium africanum S. Hughes Miscanthus , Panicum, Paspalum virgatum, Saccharum, leaf litter of Typha latifolia Argentina, Ghana, Solomon Islands, Venezuela Hughes (1952); Ellis (1971); McKenzie and Jackson (1986); Urtiaga (1986); Tarda et al. (2019)
D. lilliputeum P. Rag. Rao and D. Rao Leaf litter of Bambusa India Rao and Rao (1964); Sushma et al. (2020)
D. microsporum P. Rag. Rao and D. Rao Dead leaves of Borassus flabellifer India Rao and Rao (1964)
D. rabaulense Matsush. Brassica campestris , Dendrocalamus strictus, Gossypium, Xylia xylocarpa, air and soil Bismarck Archipelago, Britain, Congo, India, New Caledonia, Nigeria, Tanzania. Kobayasi et al. (1971); Ellis (1976); Bhat (2010)
D. sacchari (J.A. Stev.) Damon = D. quadratum S. Hughes Dead stems and leaves of Ananas, Bambusa, Borassus, Cassia, Cosmos bipinnatus, Cymbopogon, Delonix elata, Dracaena, Erythrina, Lithachne pauciflora, Musa acuminata, M. paradisiaca, Neolitsea scrobiculata, Pandanus, Persea mechrantha, Phragmites, Prunus amygdalus, Saccharum sp., S. officinarum, S. spontanium, Zinnia, leaf litter of Typha latifolia, decaying plant materials of dicots Brazil, Cuba, Federated Ghana, India, Malaysia, Pakistan, Puerto Rico, Solomon Islands, Spain, States of Micronesia, Thailand, Venezuela, Zambia Hughes (1952); Subramanian (1952); Nair and Tyagi (1961); Srivastava et al. (1964); Dennis (1970); Ellis (1971); Matsushima (1971); Stevenson (1975); Srivastava and Gupta (1981); Arnold (1986); McKenzie and Jackson (1986); Paul and Singh (1986); Gene et al. (1990); McKenzie and Jackson (1990); Ahmad et al. (1997); Pande and Rao (1998); Lumyong et al. (2003); Saravanan and Vittal (2007); Leão-Ferreira et al. (2010); Tarda et al. (2019)
D. synnematicum Somrith. Decaying leaves of Musa sp. India, Thailand Somrithipol (2007)

A study was undertaken to determine the saprobic fungi associated with Musa sp. (banana) in Thailand, during the dry season. Three hyphomycetous taxa that morphologically resembled Dictyoarthrinium were examined. According to our phylogenetic analyses of combined SSU, LSU, ITS and tef1-α sequence data, Dictyoarthrinium clustered in Didymosphaeriaceae (Pleosporales, Dothideomycetes) with strong statistical support, sister to Spegazzinia. Hence, we propose to transfer Dictyoarthrinium from Apiosporaceae (Xylariales, Sordariomycetes) to Didymosphaeriaceae (Pleosporales, Dothideomycetes) and introduce Dictyoarthrinium musae sp. nov. as a saprobe recorded from Musa sp. We also provide detailed morphological illustrations, descriptions and DNA sequence data for D. sacchari, recorded on Musa sp. from Thailand, which further validates the novel taxonomic placement of Dictyoarthrinium in Didymosphaeriaceae.

Materials and methods

Sample collection, morphological studies and isolation

Dead leaves of Musa sp. were collected from Thailand during the dry season (December to August) of 2018 and 2019. Specimens were transferred to the laboratory in cardboard boxes. Samples were examined with a Motic SMZ 168 Series microscope. Powder-like masses of fungal conidia were mounted in water for microscopic studies and photomicrography. The specimens were examined using a Nikon ECLIPSE 80i compound microscope and photographed with a Canon 550D digital camera fitted to the microscope. Measurements were made with the Tarosoft (R) Image Frame Work programme and images used for figures were processed with Adobe Photoshop CS3 Extended v. 10.0 software (Adobe Systems, USA).

Single spore isolation was carried out following the method described in Chomnunti et al. (2014). Germinated spores were individually transferred to potato dextrose agar (PDA) plates and incubated at 25 °C in daylight. Colony characteristics were observed and measured after 3 weeks at 25 °C. Herbarium specimens were deposited in the Mae Fah Luang University (MFLU) Herbarium, Chiang Rai, Thailand. Living cultures were deposited in the Culture Collection of Mae Fah Luang University (MFLUCC). Faces of fungi numbers (Jayasiri et al. 2015) and MycoBank numbers (http://www.MycoBank.org) were obtained for the respective taxa.

DNA extraction, PCR amplification and sequencing

Fungal isolates grown on potato dextrose agar (PDA) for 4 weeks at 25 °C were used to extract total genomic DNA. DNA was extracted from 50 to 100 mg of axenic mycelium of the 4-weeks-old growing cultures. The mycelium was ground to a fine powder in liquid nitrogen and fungal DNA was extracted using the Biospin Fungus Genomic DNA Extraction Kit-BSC14S1 (BioFlux, P.R. China) according to the manufacturer’s instructions. Four gene regions, the internal transcribed spacer (ITS), partial 18S small sub unit (SSU), partial 28S large sub unit (LSU) and partial translation elongation factor 1-alpha gene (tef1-α) were amplified using ITS5/ITS4 (White et al. 1990), NS1/NS4 (White et al. 1990), LR0R/LR5 (Vilgalys and Hester 1990) and EF1-983F /EF1-2218R (Rehner 2001) primers, respectively.

Polymerase chain reactions (PCR) were conducted according to the following protocol. The total volume of the PCR reaction was 25 μl and consisted of 12.5 μl of 2 × Power Taq PCR MasterMix (a premix and ready to use solution, including 0.1 Units/μlTaq DNA Polymerase, 500 μm dNTP Mixture each (dATP, dCTP, dGTP, dTTP), 20 mM Tris-HCl pH 8.3, 100 mMKCl, 3 mM MgCl2, stabiliser and enhancer), 1 μl of each primer (10 pM), 2 μl genomic DNA extract and 8.5 μl double distilled water (ddH2O). The reaction was conducted by running for 40 cycles. The annealing temperature was 56 °C for ITS and LSU, 57.2 °C for tef1-α and 55 °C for SSU and initially 95 °C for 3 min, denaturation at 95 °C for 30 seconds, annealing for 1 min, elongation at 72 °C for 30 seconds and final extension at 72 °C for 10 min for all gene regions. PCR amplification was confirmed on 1% agarose electrophoresis gels stained with ethidium bromide. The amplified PCR fragments were sent to a commercial sequencing provider (TsingKe Biological Technology Co., Beijing, China). The nucleotide sequence data acquired were deposited in GenBank.

Sequence alignment

Sequences obtained in this study were subjected to BLAST search in GenBank (https://blast.ncbi.nlm.nih.gov/Blast.cgi). BLAST search results and initial morphological studies supported that our isolates belong to Didymosphaeriaceae. Other sequences used in the analyses were obtained from GenBank based on recently published papers (Tanaka et al. 2015; Jayasiri et al. 2019) (Table 2) and BLAST search results. The single gene alignments were done by MAFFT v. 7.036 (http://mafft.cbrc.jp/alignment/server/large.html; Katoh et al. 2019) using the default settings and later refined, where necessary, using BioEdit v. 7.0.5.2 (Hall 1999).

Table 2.

Selected taxa with their corresponding GenBank accession numbers in the family Didymosphaeriaceae that are used in the phylogenetic analyses. Type strains are indicated as superscript T and newly-generated strains are indicated in bold.

Taxa Culture collection ITS LSU SSU tef1-α
Alloconiothyrium aptrootii CBS 980.95T JX496121 JX496234 NA NA
A. aptrootii CBS 981.95T JX496122 JX496235 NA NA
Austropleospora archidendri CBS 168.77T JX496049 JX496162 NA NA
A. keteleeriae MFLUCC 18-1551T NR_163349 MK348021 MK347910 MK360045
Bambusistroma didymosporum MFLU 15-0057T KP761733 KP761730 KP761737 KP761727
B. didymosporum MFLU 15-0058 KP761734 KP761731 KP761738 KP761728
Bimuria novae zelandiae CBS 107.79T MH861181 AY016356 AY016338 DQ471087
Chromolaenicola lampangensis MFLUCC 17-1462T MN325016 MN325004 MN325010 MN335649
C. thailandensis MFLUCC 17-1510T MN325018 MN325006 MN325012 MN335651
Cylindroaseptospora leucaenae MFLUCC 17-2424T NR_163333 NG_066310 MK347856 MK360047
Deniquelata barringtoniae MFLUCC 11-0422T NR_111779 NG_042696 JX254656 NA
D. vittalii NFCCI4249T MF406218 MF182395 MF622059 MF182398
Dictyoarthrinium musae MFLUCC 20-0105T MT482323 MT482320 MT482326 MT495602
D. musae MFLUCC 20-0106T MT482324 MT482321 MT482327 MT495603
D. sacchari MFLUCC 20-0107 MT482325 MT482322 MT482328 NA
D. sacchari CBS 529.73 NA MH872479 NA NA
Didymocrea sadasivanii CBS 438.65T MH858658 DQ384103 NA NA
Didymosphaeria rubi-ulmifolii MFLUCC 14-0023T NA KJ436586 NG_063557 NA
D. rubi-ulmifolii MFLUCC 14-0024 NA KJ436585 KJ436587 NA
Kalmusia italica MFLUCC 14-0560T KP325440 KP325441 KP325442 NA
K. variisporum CBS 121.517T NR_145165 JX496143 NA NA
Kalmusibambusa triseptata MFLUCC 13-0232T KY682697 KY682695 KY682696 NA
Karstenula rhodostoma CBS 690.94 NA GU301821 GU296154 GU349067
K. rhodostoma CBS 691.94 LC014559 AB807531 AB797241 AB808506
Laburnicola hawksworthii MFLUCC 13-0602T KU743194 KU743195 KU743196 NA
L. muriformis MFLUCC 14-0921T KU743200 KU743201 KU743202 NA
Letendraea cordylinicola MFLUCC 11-0150 KM213996 KM213999 KM214002 NA
L. cordylinicola MFLUCC 11-0148T NR_154118 NG_059530 KM214001 NA
Montagnula bellevaliae MFLUCC 14-0924T KT443906 KT443902 KT443904 KX949743
M. cirsii MFLUCC 13-0680 KX274242 KX274249 KX274255 KX284707
M. scabiosae MFLUCC 14-0954T KT443907 KT443903 KT443905 NA
Neokalmusia brevispora KT 1466T LC014573 AB524600 AB524459 AB539112
N. scabrispora KT 1023 LC014575 AB524593 AB524452 AB539106
Neptunomyces aureus CMG12T MK912121 NA NA MK948000
N. aureus CMG13 MK912122 NA NA MK948001
Paracamarosporium fagi CPC 24890 KR611886 KR611904 NA NA
P. fagi CPC 24892T KR611887 KR611905 NA NA
Paraconiothyrium cyclothyrioides CBS 972.95T JX496119 JX496232 AY642524 NA
Paramassariosphaeria anthostomoides CBS 615.86 MH862005 GU205223 GU205246 NA
P. anthostomoides MFLU 16-0172T KU743206 KU743207 KU743208 NA
Paraphaeosphaeria rosae MFLUCC 17-2549T MG828937 MG829046 MG829152 MG829223
P. rosicola MFLUCC 15-0042T NR_157528 MG829047 MG829153 NA
Phaeodothis winteri CBS 182.58 NA GU301857 GU296183 NA
Pseudocamarosporium propinquum MFLUCC 13-0544 KJ747049 KJ813280 KJ819949 NA
P. pteleae MFLUCC 17-0724T NR_157536 MG829061 MG829166 MG829233
Pseudopithomyces entadae MFLUCC 17-0917T NA NG_066305 MK347835 MK360083
P. rosae MFLUCC 15-0035T MG828953 MG829064 MG829168 NA
Spegazzinia bromeliacearum URM 8084T MK804501 MK809513 NA NA
S. deightonii MFLUCC 20-0002 MN956768 MN956772 MN956770 NA
S. intermedia CBS 249.89T MH862171 MH873861 NA NA
S. lobulata CBS 361.58T MH857812 MH869344 NA NA
S. musae MFLUCC 20-0001T MN930512 MN930514 MN930513 NA
S. neosundara MFLUCC 15-0456T KX965728 KX954397 KX986341 NA
S. radermacherae MFLUCC 17-2285T MK347740 MK347957 MK347848 MK360088
S. tessarthra SH 287 JQ673429 AB807584 AB797294 AB808560
Tremateia arundicola MFLU 16-1275T KX274241 KX274248 KX274254 KX284706
T. guiyangensis GZAAS01T KX274240 KX274247 KX274253 KX284705
T. murispora GZCC 18-2787T NR_165916 MK972751 MK972750 MK986482
Verrucoconiothyrium nitidae CBS:119209 EU552112 NA NA NA
Xenocamarosporium acaciae CBS:139895 NR_137982 NG_058163 NA NA
X. acaciae MFLUCC 17-2432 MK347766 MK347983 MK347873 MK360093

Phylogenetic analyses

Maximum Likelihood (ML) trees were generated using the RAxML-HPC2 on XSEDE (8.2.8) (Stamatakis et al. 2008; Stamatakis 2014) in the CIPRES Science Gateway platform (Miller et al. 2010) using GTR+I+G model of evolution. Bootstrap supports were obtained by running 1000 pseudo-replicates. Maximum Likelihood bootstrap values (ML) ≥ 60% are given above each node of the phylogenetic tree in blue (Fig. 1).

Figure 1. 

Maximum Likelihood tree revealed by RAxML from an analysis of SSU, LSU and ITS and tef1-α sequence data of the genera of Didymosphaeriaceae, showing the phylogenetic position of Dictyoarthrinium musae (MFLUCC 20-0105, MFLUCC 20-0106) and D. sacchari (MFLUCC 20-0107). ML bootstrap supports (≥ 60%) and Bayesian posterior probabilities (≥ 0.95 BYPP) are given above the branches, respectively. The tree is rooted with Bambusistroma didymosporum (MFLU 15-0057 and MFLU 15-0058). Strains generated in this study are indicated in brown bold type. Ex-type strains are indicated in black bold. The scale bar represents the expected number of nucleotide substitutions per site.

Bayesian analysis was conducted with MrBayes v. 3.1.2 (Huelsenbeck and Ronquist 2001) to evaluate posterior probabilities (PP) (Rannala and Yang 1996; Zhaxybayeva and Gogarten 2002) by Markov Chain Monte Carlo sampling (BMCMC). Two parallel runs were conducted, using the default settings, but with the following adjustments: four simultaneous Markov chains were run for 2,000,000 generations, trees were sampled every 100th generation and 20,001 trees were obtained. The first 4,000 trees, representing the burn-in phase of the analyses, were discarded. The remaining 16,001 trees were used for calculating PP in the majority rule consensus tree. Branches with Bayesian posterior probabilities (BYPP) ≥ 0.95 are indicated above each node of the phylogenetic tree (Fig. 1). Phylogenetic trees were visualised with the FigTree v1.4.0 programme (Rambaut 2011).

Results

Phylogenetic analyses

The combined SSU, LSU, ITS and tef1-α matrix comprised 61 sequences that represents the genera in Didymosphaeriaceae. The best scoring RAxML tree is shown (Fig. 1) with a final ML optimisation likelihood value of -19278.64. The matrix had 1091 distinct alignment patterns, with 39.08% of undetermined characters or gaps. Estimated base frequencies were: A = 0.234095, C = 0.252628, G = 0.278053, T = 0.235224; substitution rates AC = 1.252730, AG = 2.198875, AT = 1.318760, CG = 0.953798, CT = 5.276095, GT = 1.000000; proportion of invariable sites I = 0.491333; gamma distribution shape parameter α = 0.446418. All trees (ML and BYPP) were similar in topology and did not differ at the generic relationships, which are in agreement with multi-gene phylogeny of Tanaka et al. (2015) and Jayasiri et al. (2019). All Dictyoarthrinium strains analysed herein clustered as a highly-supported monophyletic clade (ML = 100%, BYPP = 1.00) in Didymosphaeriaceae (Fig. 1) sister to Spegazzinia (ML = 75%, BYPP = 0.98). We have included LSU sequence data of D. sacchari (CBS 529.73) of Vu et al. (2019) in our phylogenetic analyses. According to GenBank, CBS 529.73 was classified in Apiosporaceae (Sordariomycetes). In our analyses, D. sacchari (CBS 529.73) clustered with MFLUCC 20-0105, MFLUCC 20-0106 and MFLUCC 20-0107 strains in Didymosphaeriaceae with a strong statistical support (ML = 100%, BYPP = 1.00). Our strain MFLUCC 20-0107 grouped with D. sacchari (CBS 529.73). The novel isolates of D. musae (MFLUCC 20-0105 and MFLUCC 20-0106) were sister to D. sacchari (CBS 529.73 and MFLUCC 20-0107) with strong statistical support (ML = 100%, BYPP = 1.00).

Taxonomy

Dictyoarthrinium musae Samarakoon, Chomnunti & K.D. Hyde, sp. nov.

MycoBank No: MycoBank No: 835764
Figure 2

Etymology

Name reflects the host genus, Musa (Musaceae).

Holotype

MFLU 20-0437

Description

Saprobic on dead leaves of Musa sp. Sexual morph: Undetermined. Asexual morph: Colonies compact or effuse, black, often pulvinate. Mycelium superficial, a close network of branched and anastomosing hyphae. Stromata none. Setae and hyphopodia absent. Conidiophores 30–140 × 1–2 μm (x¯ 81.5 × 1.6 μm, n = 25), basauxic, arising usually singly from subspherical, subhyaline to light brown conidiophore mother cells, 4.5–4.8 × 4.3–4.5 μm (x̄ = 4.6 × 4.4 μm, n = 10), macronematous, mononematous, straight or flexuous, narrow, cylindrical, rough, subhyaline to pale brown, with thick brown or dark brown transverse septa that appear as stripes with distances of 6.3–5.8 μm at apex and 2.3–3 μm at base of the conidiophore. Conidiogenous cells 4.1–4.5 × 4.3–4.7 μm (x̄ = 4.4 × 4.5 μm, n = 10), blastic, integrated, terminal and intercalary, cylindrical, smooth, denticles absent, hyaline. Conidia 7–11.5 × 6.5–9 μm (x̄ = 8.7 × 7.9 μm, n = 40), solitary, dry, acropleurogenous, simple, square, rounded at the corners, 4-celled, spherical or subspherical, often flattened in one plane, pale to dark brown at maturity, verrucose, with light brown to dark brown warts, immature conidia often 1-celled and subhyaline. Terminal conidium with four cells, sometimes absent or fallen before lateral conidia, mature conidia split along one line of the septa, most conidia arranged obliquely downwards on the conidiophore, conidial formation observed as a bunch starting after conidiophore 1–3 septate.

Culture characteristics

Conidia germinating on PDA within 18 hrs. Colonies on PDA reaching a diameter of 50 mm after 14 days at 25 °C, slightly raised, hairy, filamentous, moderately dense, middle light grey, periphery white; reverse white to greyish-white.

Material examined

THAILAND. Chiang Rai. On dead leaves of Musa sp. (Musaceae), 7 December 2018, M. C. Samarakoon, BNS265 (MFLU 20-0437, holotype), ex-type living culture (MFLUCC 20-0105); ibid. 20 February 2019, B. C. Samarakoon BNS2239 (MFLU 20-0438, paratype), ex-paratype living culture (MFLUCC 20-0106).

Notes

Based on BLAST search results of SSU, LSU, ITS and tef1-α sequence data, Dictyoarthrinium musae (MFLUCC 20-0105 and MFLUCC 20-0106) showed high similarity as follows: SSU = 99.15% to Paraconiothyrium hawaiiense (CBS 120025), LSU = 95.57% to Cylindroaseptospora siamensis (MFLUCC 17-2527), ITS = 98.24% to Kalmusia italica (isolate 5), tef1-α = 97.75% to Spegazzinia neosundara (MFLUCC 13-0211) with 100%, 100%, 87% and 99% query covers, respectively. In the multigene phylogeny, the Dictyoarthrinium clade was sister to Spegazzinia (ML = 75%, BYPP = 0.98). Within the Dictyoarthrinium clade, D. musae (MFLUCC 20-0105 and MFLUCC 20-0106) separated from the sister taxon, D. sacchari with strong statistical support (ML = 100%, BYPP = 1.00). ITS sequence comparison revealed 7.84% base pair differences between D. musae and D. sacchari (MFLUCC 20-0107), which is in agreement with the new species concept outlined by Jeewon and Hyde (2016). Dictyoarthrinium musae differs from D. sacchari by its unique conidial development in the apex. The terminal conidia of D. musae are always 4-celled and similar in colour to mature lateral conidia. In addition, the terminal conidia of D. musae are sometimes absent or fallen before the lateral conidia. In contrast, the terminal conidia of D. sacchari can be 2-celled or 4-celled, pale brown with respect to lateral mature conidia and always persist on the conidiophore. In addition, the mature conidia of D. musae split along one line of the septa and this specific feature is absent in D. sacchari. Dictyoarthrinium musae has a subhyaline, spherical conidiophore mother cell while D. sacchari has a distinct cup-shaped, brown conidiophore mother cell. Therefore, based on contrasting morphological differences to D. sacchari and strong statistical support from our molecular phylogeny, D. musae is herein introduced as a new species.

Figure 2. 

Dictyoarthrinium musae (MFLU 20-0437, holotype) a conidia on the host b conidiophore and conidia with conidiophore mother cell c–f conidia with conidiophores on stalk g developmental stage of an immature lateral conidium h four-celled terminal conidium i conidiophore j conidiophores and conidia with terminal conidium k, l conidiophores without terminal conidium m attachment of a mature lateral conidium n–q warted four-celled mature conidia r, s mature conidia that split at septa t colony on PDA after 21 days. Scale bars: 500 μm (a); 50 μm (b, c); 20 μm (d–g, i); 10 μm (h); 5 μm (j–s).

Dictyoarthrinium sacchari (J.A. Stev.) Damon, Bull. Torrey bot. Club 80: 164 (1953)

Figure 3

Description

Saprobic on dead leaves of Musa sp. Sexual morph: Undetermined. Asexual morph: Colonies compact or effuse, black, often pulvinate. Mycelium superficial, a close network of branched and anastomosing hyphae. Stromata none. Setae and hyphopodia absent. Conidiophores 50–110 × 1–2 μm (x̄ = 72.0 × 1.6 μm, n = 15), basauxic, arising from cup-shaped, brown, distinct conidiophore mother cells, 3.4–4.4 × 2.9–4.7 μm (x̄ = 4 × 3.7 μm, n = 10), macronematous, mononematous, usually straight or flexuous, narrow, cylindrical, rough-walled, subhyaline to pale brown, with dark brown transverse septa as stripes with distances of 6.3–5.8 μm at apex and 2.3–3 μm at base of the conidiophore. Conidiogenous cells 4–4.5 × 4.3–4.7 μm (x̄ = 4.4 × 4.5 μm, n = 10), blastic, integrated, terminal and intercalary, cylindrical, smooth, hyaline. Conidia at maturity 8.5–11.5 × 8.5–10 μm (x̄ = 9.9 × 9.3 μm, n = 40), solitary, dry, acropleurogenous, simple, square, rounded at the corners, 4-celled, but difficult to distinguish the cells due to their blackish-brown nature, spherical or subspherical, often flattened in one plane, blackish-brown at maturity, with brown warts on surface of the cells, terminal conidium always 4-celled or 2-celled, light brown when compared with lateral conidia, most conidia arranged perpendicular to the conidiophore, some directed obliquely upwards.

Culture characteristics

Conidia germinating on PDA within 18 hrs. Colonies on PDA reaching a diameter of 55 mm after 14 days at 25 °C, raised, moderately dense, entire margined, brownish-grey at maturity; reverse white to greyish-white.

Material examined

Thailand, Chiang Mai. On mid-rib of a dead leaf of Musa sp. (Musaceae), S. Phongeun, 18 July 2018, BNS2287, (MFLU 20-0439), living culture MFLUCC 20-0107.

Notes

Based on BLAST search results of SSU, LSU, ITS and tef1-α sequence data, our strain (MFLUCC 20-0107) showed high similarity to the taxa in GenBank as follows (SSU = 99.26% to Paraconiothyrium brasiliense (isolate GF1), LSU = 96.14% to Alloconiothyrium aptrooti (CBS 981.95), ITS = 93.00% to Kalmusia italica (MFLUCC 13-0066). In the multigene phylogeny, MFLUCC 20-0107 groups with Dictyoarthrinium sacchari, sister to D. musae with strong statistical support (ML = 100%, BYPP = 1.00). Our strain shares similar morphological features with D. sacchari (Subramanium 1952; Ellis 1971) and did not differ significantly. There are slight differences in conidial dimensions and the length of conidiophores of our collection and other D. sacchari collections by previous studies. Conidial dimensions and the length of conidiophores may differ due to diverse environmental effects and host associations. LSU sequence data of D. sacchari (CBS 529.73) are identical with our strain (MFLUCC 20-0107). Unfortunately, ITS, SSU and tef1-α sequence data of CBS 529.73 are not available in GenBank to compare with our strain. LSU data of Dictyoarthrinium musae have 2.24% of base pair difference with D. sacchari (CBS 529.73 and MFLUCC 20-0107). Dictyoarthrinium sacchari was reported on Musa sp. from Thailand in Lumyong et al. (2003) without morpho-molecular justifications. In this study, we document D. sacchari with detailed morphological illustrations, description, herbarium material and a living culture coupled with DNA sequence data (SSU, LSU, ITS) for a better taxonomic resolution.

Figure 3. 

Dictyoarthrinium sacchari (MFLU 20-0439) a conidia on the host b developmental stage of terminal conidium attached to the conidiophore c–f Conidiophores and conidia (e, with distinct mother cell) g, h mature conidiophores with four-celled terminal conidium i conidiophore with two celled terminal conidium j developmental stages of conidia on conidiophore k colony on PDA after 21 days l–q conidia. Scale bars: a = 1000 μm (a); 20 μm (b, j); 50 μm (c–i); 5 μm (l–q).

Discussion

Both Dictyoarthrinium and Spegazzinia are characterised by basauxic conidiophores (Hughes 1952; Ellis 1971; Tanaka et al. 2015). Spegazzinia often has stellate (α) and disc-shaped (β) conidia (Ellis 1971; Tanaka et al. 2015). The conidia of Dictyoarthrinium (except D. africanum) share some similar characteristics with disc-shaped, β conidia of Spegazzinia. Both conidia are brown, 4-celled and constricted at the septa. Conidia of Dictyoarthrinium have characteristic hyaline or brown warts. Rarely, some taxa of Spegazzinia, for example, S. deightonii, also bear blunt ended spines. Most disc-shaped conidia of Spegazzinia are not warted. In addition, stellate conidia of Spegazzinia are always 4–5-celled and spinulose (Ellis 1971; Tanaka et al. 2015). There are contrasting morphological features of the basauxic conidiophores of both genera. The conidiophores of Dictyoarthrinium are hyaline to subhyaline with septa that appear as dark brown or light brown stripes throughout the conidiophore. The conidiophores (in stellate conidia) of Spegazzinia are more elongated, narrow, aseptate and dematiaceous.

Dictyoarthrinium quadratum (type of Dictyoarthrinium) is the heterotypic synonym of D. sacchari. Dictyoarthrinium quadratum has a terminal mature conidium with one to two cells. As described in Hughes (1952), these 2-celled conidia remain on the conidiophore, even when other conidia fall off. This feature is absent in D. musae. The terminal conidium of D. musae always ends up with four cells. The conidia of D. quadratum are obliquely upwardly directed, whereas the conidia of D. musae are obliquely downwardly directed (Fig. 2). The conidiophores of D. quadratum are erect and straight while D. musae has more curved conidiophores.

Dictyoarthrinium africanum differs significantly from D. musae by having 16-celled conidia. The conidia of D. rabaulense are completely black and densely echinulate with spines sometimes up to 4 μm long (Ellis 1976). However, D. musae has brown warts on the surface of conidia, while D. lilliputeum has hyaline warts. Dictyoarthrinium microsporum has longer conidiophores (250 μm) than D. musae. Morphological features of Dictyoarthrinium species are illustrated in Fig. 4. A key to the species of Dictyoarthrinium is provided below.

Figure 4. 

Morphology of conidia and conidiophores of previously described Dictyoarthrinium species a, d D. microsporum b, i D. synnematicum c, e D. lilliputeum f, j D. africanum g, h, k D. rabaulense. Scale bars: 20 μm (a, c, d, e); 10 μm (b, i). Magnification × 650 (f, g, h, j, k). Redrawn from Rao and Rao (1964), Ellis (1971), Kobayasi et al. (1971) and Somrithipol (2007).

Key to the species of Dictyoarthrinium

1 Synnemata present D. synnematicum
Synnemata absent 2
2 Conidia 2- or 4-celled 3
Conidia 16-celled D. africanum
3 Conidia with brown warts 4
Conidia with hyaline warts D. lilliputeum
4 Conidiophores up to 130 μm long 5
Conidiophores up to 250 μm long D. microsporum
5 Terminal conidium always 4-celled, mature conidia split along one line of the septa D. musae
Terminal conidium 2- or 4-celled, mature conidia do not split along septa D. sacchari

To date, the taxonomy and phylogeny of most genera that have basauxic conidiogenesis (Hughes 1952) have been resolved with their correct taxonomic placements. Dictyoarthrinium and Endocalyx represented the sole unresolved genera. We transferred Dictyoarthrinium to Didymosphaeriaceae based on morphological and molecular evidence. This study uses multigene sequence data of SSU, LSU, ITS and tef1-α for the first time to confirm the taxonomic placement of Dictyoarthrinium in Didymosphaeriaceae.

Acknowledgements

Samantha C. Karunarathna would like to thank the CAS President’s International Fellowship Initiative (PIFI) young staff under the grant number: 2020FYC0002 for funding his postdoctoral research and the National Science Foundation of China (NSFC, project code 31851110759) for partially funding this work. Rungtiwa Phookamsak thanks CAS President’s International Fellowship Initiative (PIFI) for young staff (grant no. Y9215811Q1), the National Science Foundation of China (NSFC) project code 31850410489 (grant no. Y81I982211) and Chiang Mai University for their partial support of this research work. Dhanushka Wanasinghe thanks CAS President’s International Fellowship Initiative (PIFI) for funding his postdoctoral research (number 2019PC0008), the National Science Foundation of China and Chinese Academy of Sciences for financial support under the grant 41761144055. K.D Hyde thanks Thailand research grants entitled “The future of specialist fungi in a changing climate: baseline data for generalist and specialist fungi associated with ants, Rhododendron species and Dracaena species (Grant No: DBG6080013) and “Impact of climate change on fungal diversity and biogeography in the Greater Mekong Sub region (Grant No: RDG6130001). Binu C. Samarakoon offers her sincere gratitude to S. Phongeun, G. Samarakoon, Seetha Malani, Thiue Samarakoon and A.J Gajanayake for the valuable support they have given.

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