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Blastosporium persicolor gen. et sp. nov., a new helotialean fungus
expand article infoHua Zheng, ZhenNa Zhang§, Zhijia Wen§, Rafael F. Castañeda-Ruiz|, ZeFen Yu§
‡ Yunnan University, Kunming, China
§ Xiamen Tobacco Industrial CO., LTD, Xiamen, China
| Associate Research of Instituto de Investigaciones Fundamentales en Agricultura Tropical Alejandro de Humboldt, Habana, Cuba
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Abstract

A new genus and species, Blastosporium persicolor, is described and illustrated from leaves of mildewed tobacco. It is characterised by branched, septate hyphae from which arise macronematous, unbranched or spaced branched conidiophores and mono- or polyblastic conidiogenous cells that produced solitary and blastocatenate, obovoid, oblong, ellipsoidal, allantoid, broad fusiform to irregular, unicellular, hyaline conidia. The phylogenetic analyses, based on the combined sequence data from the small and large nuclear subunit ribosomal DNA (SSU and LSU), placed B. persicolor in the Leotiomycetes class, Helotiales order.

Keywords

Ascomycota, Pezizomycotina, phylogeny, Nicotiana tabacum

Introduction

The Kingdom Fungi contains a huge number of species, which continues to rise with more collections. With the advance in the studies of DNA sequence data, the fungal classification system has been updated over the years. Many described species obtained new taxonomic status after the molecular data and have been processed. Leotiomycetes is a large class in Ascomycota and has potential taxonomic value relating to the ecology and biology. The traditional classification of Leotiomycetes at high levels has experienced considerable challenges with the inclusion of the molecular techniques in systematics studies. For example, early research accepted five orders, 21 families and about 510 genera in the Leotiomycetes on the basis of both traditional classification and molecular phylogenetic studies (Eriksson 2005, Kirk et al. 2001), but a recent study reported a new classification of Leotiomycetes, including 11 orders, 44 families and about 590 genera (Wijayawardene et al. 2018) and this classification also lacks sufficient DNA sequence data. In Leotiomycetes, the order Helotiales, one of the largest non-lichen-forming ascomycetous groups, is composed of fungi of diverse morphology and ecology. Of these, members of the Helotiales thrive in various ecosystems and cover a broad range of niches and helotialean fungi have been found as plant pathogens, endophytes, nematode-trapping fungi, mycorrhizae, ectomycorrhizal parasites, fungal parasites, terrestrial saprobes, aquatic saprobes, root symbionts and wood rot fungi (Wang et al. 2006).

During a survey of fungi growing on mildewed tobacco leaves, an unknown fungus was found. Based on its morphological characters and DNA sequence data, it is proposed as a new asexual genus and species, Blastosporium persicolor.

Materials and methods

Isolation and morphological study of strain

Samples of the mildewed tobacco leaves were collected from Xiamen Logistics Warehousing Center. Samples were preserved in zip-locked plastic bags, labelled and transported to the laboratory. The procedure was as follows: samples (5g) were placed in PDA liquid medium (200 g potato, 20 g glucose, 1000 ml distilled water), shaken at 140 rpm/min for 1 h and the filtrate was collected. The filtrate was coated on a CMA plate (20 g cornmeal, 10 g agar, 1000 ml distilled water) at 28 °C, supplemented with two antibiotics (penicillin G, 0.5 g/l; and streptomycin, 0.5 g/l; Gams et al. 1998). After 3–5 days, single colonies were isolated into pure culture, grown on potato dextrose agar plates (PDA). The characteristics of the colonies were from PDA, CMA and SNA (synthetic low nutrient agar). Microscopic characteristics were made from cultures growing on CMA after incubation at room temperature for one week.

The pure cultures and dried cultures were deposited in the Herbarium of the Laboratory for Conservation and Utilization of Bio-resources, Yunnan University, Kunming, Yunnan, P.R. China (YMF, formerly Key Laboratory of Industrial Microbiology and Fermentation Technology of Yunnan).

DNA extraction, polymerase chain reaction (PCR) amplification and sequencing

Pure cultures were grown on PDA for 5 days at 25 °C. Actively growing mycelium was scraped off the surface of a culture and transferred to 2 ml Eppendorf micro-centrifuge tubes. Total genomic DNA was extracted according to the procedures in Turner et al. (1997). Primers used for PCR amplification and sequencing of nucSSU rDNA, nucLSU rDNA and ITS rDNA were NS1-NS4, LROR-LR7 and ITS1-ITS4, respectively (White et al. 1990, Vilgalys and Hester 1990). Detailed protocols and PCR conditions for the amplification were fully described by Su et al. (2015). PCR products were then purified using a commercial Kit (Bioteke Biotechnology Co, Ltd, China) and forward and reverse sequences with a LI-COR 4000L automatic sequencer, using a Thermo Sequenase-kit, as described by Kindermann et al. (1998). The sequences were deposited in the National Center for Biotechnology Information (NCBI) and the accession numbers are listed in Table 1.

Strains and the GenBank accession numbers of sequences used in the molecular phylogenetic analyses in this study.

Name Strain GenBank accession number
LSU SSU
Arthonia caesia (Flot) Körb. AFTOL-ID 775 FJ469668
Arthrobotrys elegans (Subram & Chandrash) Seifert & W.B. Kendr. AFTOL-ID 1252 FJ176864 FJ176810
Arthrocladiella mougeotii (Lév) Vassilkov AB022379 AB033477
Blastosporium persicolor Z. F. Yu & H. Zheng YMF1.05546 MH992517 MH992516
Blumeria graminis (DC.) Speer AB022362 AB033476
Brasiliomyces trinus (Harkn) R.Y. Zheng AB022350
Bryoglossum gracile (P. Karst.) Redhead MBH52481 AY789420 AY789419
Bulgaria inquinans (Pers.) Fr. ZW-Geo52-Clark AY789344 AY789343
Candida albicans (C.P. Robin) Berkhout WO1 L28817 X53497
Capnodium coffeae Pat. CBS 147.52 DQ247800 DQ247808
Chlamydotubeufia huaikangplaensis Boonmee & K.D. Hyde MFLUCC10-0926 JN865198
Ciboria batschiana (Zopf) N. F. Buchw. WZ-JXD-22 AY789322
Cudonia circinans (Pers.) Fr. OSC56399 AF279379 AF107343
Cyttaria darwinii Berk. 14 EU107208 EU107181
Dermea acerina (Peck) Rehm CBS 161.38 DQ247801 DQ247809
Disciotis venosa (Pers.) Arnould AFTOL-ID 179 AY544667 AY544711
Dothidea sambuci (Pers.) Fr. AFTOL-ID 274 AY544681 AY544722
Erysiphe australiana (McAlpine) U. Braun & S. Takam. AB022407
Erysiphe cornicola Meeboon & S. Takam. AB022389
Erysiphe glycines F. L. Tai MUMH52 AB022397 AB120748
Erysiphe gracilis R. Y. Zheng & G. Q. Chen AB022357
Erysiphe mori (I. Miyake) U. Braun & S. Takam. AB022418 AB033484
Erysiphe simulans (E. S. Salmon) U. Braun & S. Takam. AB022395
Eupenicillium limosum S. Ueda AFTOL-ID 2014 EF411064 EF411061
Fabrella tsugae (Farl) Kirschst. AF356694
Geoglossum glabrum Pers. OSC60610 AY789317 AY789316
Geoglossum umbratile Sacc. Mycorec1840 AY789303 AY789302
Helicoma chlamydosporum Shearer CBS 160.69 AY856875 AY856923
Helicoma vaccinii Carris CBS 216.90 AY856879 AY856926
Helicomyces roseus Link CBS 283.51 AY856881 AY856928
Helicosporium guianense Linder CBS 269.52 AY856893 AY856938
Holwaya mucida (Schulzer) Korf & Abawi B 70 0009352 DQ257356 DQ257355
Lachnum bicolor (Bull.) P. Karst. AFTOL-ID 177 AY544674 AY544690
Lachnum virgineum (Batsch) P. Karst. AFTOL-ID 49 AY544646 AY544688
Leotia lubrica (Scop.) Pers. ZW-Geo59-Clark AY789359 AY789358
Monascus purpureus Went AFTOL-ID 426 DQ782908 DQ782881
Morchella esculenta (L.) Pers. AFTOL-ID 60 AY544664 AY544708
Mycosphaerella punctiformis (Pers.) Starbäck AFTOL-ID 942 DQ470968 DQ471017
Neoerysiphe galeopsidis (DC.) U. Braun AB022369
Neofabraea malicorticis (Cordley) H.S. Jacks. AFTOL-ID 149 AY544662 AY544706
Orbilia vinosa (Alb. & Schwein.) P. Karst. AFTOL-ID 905 DQ470952 DQ471000
Penicillium freii Frisvad & Samson DAMO 216705 AY640958 AY640998
Phyllactinia moricola (Henn.) Homma AB022401 AB033481
Piceomphale bulgarioides (P. Karst.) Svrček 1589.P Z81415
Pleochaeta shiraiana (Henn.) Kimbr. & Korf MUMH36 AB022403 AB120750
Podosphaera tridactyla (Wallr.) de Bary AB022393
Roccellographa cretacea J. Steiner AFTOL-ID 93 DQ883696 DQ883705
Rutstroemia bolaris (Batsch) Rehm 1526.P Z81419.1
Sawadaea polyfida (C.T. Wei) R.Y. Zheng & G.Q. Chen AB022364
Schismatomma decolorans (Erichsen) Clauzade & Vězda DUKE 0047570 NG_027622 NG_013155
Scleromitrula shiraiana (Henn.) S. Imai Hirayama062001 AY789407 AY789406
Sclerotinia sclerotiorum (Lib.) de Bary WZ0067 AY789347 AY789346
Spathularia flavida Pers. wz138 AF433142 AY789356
Thaxteriella inthanonensis Boonmee & K.D. Hyde MFLUCC11-0003 JN865199
Trichoglossum hirsutum (Pers.) Boud. AFTOL-ID 64 AY789313 AY789312
Vibrissea flavovirens (Pers.) Korf & J.R. Dixon MBH39316 AY789426 AY789425
Vibrissea truncorum (Alb. & Schwein) Fr. CUP-62562 AY789402 AY789401

Sequence alignment and phylogenetic analysis

Other fungal sequences were obtained from the GenBank nucleotide database. DNA sequence data were aligned using ClustalX 1.83 (Higgins 1994) with default parameters and the consensus sequences were manually adjusted and linked in BioEdit v.7.0 (Hall 1999). Manual gap adjustments were made to improve the alignment and ambiguously aligned regions were also excluded. Portions of the 5'- and 3'-ends of the nuclear small and large subunits ribosomal DNA (nucSSU and nucLSU) were excluded from all analyses and coded by a question mark (?). MrBayes (Ronquist and Huelsenbeck 2003) was used to calculate the SSU rRNA and LSU rRNA sequence-based Bayesian inference of the phylogeny tree, with the following parameters: ngen=1,000,000; samplefr=1,000; printfr=1,000. The GenBank accession numbers of sequences used in the phylogenetic analysis are shown in Table 1 including the classes of Leotiomycetes, Arthoniomycetes, Dothideomycetes, Eurotiomycetes, Orbiliomycetes, Pezizomycetes and Sordariomycetes. Candida albicans (C.P. Robin) Berkhout (Saccharomycetes) was used as outgroup.

Results

Sequence analyses

In BLAST searches, the ITS sequence B. persicolor, MH992518, had the highest similarity of 88% with Tetracladium and 87% with Chalara (Corda) Rabenh., both belonging to Leotiomycetes. Therefore, most sequences are mainly from Leotiomycetes in the dataset. The dataset comprised 57 taxa representing 7 classes, 11 orders, 22 families and 57 species with Candida albicans as outgroup. Other DNA sequences were obtained from the GenBank. The final alignment comprised a total of 1635 base pairs (TreeBASE accession number: 23451), which combined the SSU rRNA and LSU rRNA sequences and the dataset was analysed by the Bayesian Inference method. The topologies of the tree are shown with the Bayesian posterior probabilities values for clades of analyses (Figure 1). In this tree, the new genus is phylogenetically placed in the Leotiomycetes. This monophyletic group formed a close relationship with several genera, which are grouped in this class, e.g. Vibrissea flavovirens and Vibrissea truncorum (Vibrisseaceae), Cudonia circinans and Spathularia flavida (Cudoniaceae) that are grouped with the new genus in the same clade. Therefore, analysis of partial LSU and SSU nuc rDNA sequences placed the new genus in the Leotiomycetes. Additionally, the tree also supports the fact that the Helotiales is not monophyletic.

Figure 1. 

Phylogenetic tree based on Bayesian analysis of the combined LSU and SSU sequences. Candida albicans is used as outgroup. Bayesian bootstraps were indicated by the nodes and the scale bar shows the expected changes per site. The new genus proposed is in boldface.

Taxonomy

Blastosporium Z. F. Yu & H. Zheng, gen. nov.

MycoBank No: 828280

Etymology

Latin, Blasto-, referring to the blastic conidial ontogeny, + Latin, sporium, referring to the conidia.

Type species

Blastosporium persicolor Z. F. Yu & H. Zheng

Diagnosis

Characterised by mono- and polyblastic, integrated or discrete conidiogenous cells, solitary or blastocatenate, unicellular, obovoid, oblong, ellipsoidal, allantoid conidia (5–8 × 2.3–4.1 μm). Differs from the genus Tetracladium De Wild. by macronematous or semi-macronematous conidiophores and mono- and polyblastic conidiogenous cells.

Description

Mycelium partly superficial and partly immersed, composed of branched, septate, smooth, hyaline hyphae. Conidiophores macronematous or semi-macronematous, erect or prostrate, smooth, hyaline, sometimes reduced to conidiogenous cells. Conidiogenous cells mono- and polyblastic, terminal, integrated or discrete, determinate, sometimes with sympodial elongations, smooth, hyaline. Conidia solitary or blastocatenate, acrogenous, unicellular, obovoid, oblong, ellipsoidal, allantoid, broad fusiform to irregular, smooth, hyaline.

Distribution

China.

Notes

Blastosporium is superficially similar to the genera, Acaromyces Boekhout et al. and Meira Boekhout et al. Their conidiophores are reduced to conidiogenous cells, which produce solitary or sometimes blastocatenate, unicellular, hyaline conidia by blastic conidial ontogeny. These genera are yeast-like hyphomycetes that have been connected phylogenetically with Exobasidiomycetidae (Ustilaginomycetes, Basidiomycota) (Boekhout et al. 2003, Seifert et al. 2011).

Hyphozyma de Hoog & M.T.Sm. also superficially resembles Blastosporium, but Hyphozyma is a typical yeast-like hyphomycete, characterised by undifferentiated conidiophores and conidia are unicellular, hyaline, solitary or produced in basipetal chains (de Hoog and Smith 1981, Seifert et al. 2011).

Blastosporium persicolor Z. F. Yu & H. Zheng, sp. nov.

MycoBank No: 828281
Figure 2

Etymology

Latin, persicolor, referring to the apricot colour of the colonies on PDA medium.

Description

Colonies on CMA with 1–2 concentric rings slightly curled, entire at the margin, light orange-yellowish-pinkish colour. Reverse yellowish-orange. Mycelium partly superficial and partly immersed, composed of branched, septate, smooth-walled, creeping, 2.0–3.3 μm wide hyphae. Conidiophores macronematous or semi-macronematous, mononematous, erect or prostrate, straight or flexuous, unbranched or slightly branched, hyaline, smooth-walled, 35–14.4 × 1.8–3.5 μm. Conidiogenous cells mostly monoblastic, sometime polyblastic after several sympodial elongations, integrated or discrete, terminal or intercalary, 7.0–13.1× 2.6–3.3 μm, clavate or cylindrical, with a distinct or inconspicuous denticle at the conidiogenous loci. Conidia solitary or blastocatenate, acrogenous, obovoid, oblong, ellipsoidal, subcylindrical, allantoid, broad fusiform to irregular, slightly attenuated, truncate at the base or at the ends, unicellular, smooth, hyaline, 5–8 × 2.3–4.1 μm. Sexual form unknown.

Figure 2. 

Cultures and anamorph of Blastosporium persicolor (YMF 1.05546). A–C Cultures (A on PDA B on CMA C on SNA) at 25 °C after 12 days D–H conidiophores and monoblastic conidiogenous cells I conidiophores and polyblastic conidiogenous cells J, K conidia (J one scar on conidia K multi-scars on conidia); Scale bar: 10 μm (D–K).

Culture characteristics

(in darkness, at 25 °C after 10 d). Colonies attaining 1.5–1.7 cm diam. on PDA, 1.0–1.2 cm diam. on SNA, 1.5–1.7 cm on CMA. On PDA, colonies plicated, orange, reverse pale yellow, margin smooth and entire; sporulation abundant. On SNA, colonies flat, white to cream-coloured, flocculent, reverse white, growing slowly, sporulation abundant. The fungus does not grow at 35 °C on PDA, CMA and SNA.

Type

CHINA. Xiamen, Fujian Province, 24°33'9.6"N, 117°55'7.4"E, 23 m alt., from mildewed tobacco (Nicotiana tabacum L.) leaves, June 2018, Z.N. Zhang (dried slide YMFT 1.05546, holotype; ex-type YMF 1.05546).

Discussion

To determine the phylogenetic placement of this species, Blastosporium persicolor was analysed with species from 7 classes, Leotiomycetes, Arthoniomycetes, Dothideomycetes, Eurotiomycetes, Orbiliomycetes, Pezizomycetes and Geoglossomycetes (Wang et al. 2006). By Bayesian analysis, the new genus was placed in the Helotiales, Leotiomycetes. In the tree, B. persicolor grouped with the Cudonia-Spathularia clade and Vibrissea clade, but the placement did not receive strong support. Therefore, we have temporarily designated this species as a new genus and family incertae sedis.

In the Helotiales, many genera, such as Bulgaria Fr. (Bulgariaceae), Rutstroemia P. Karst. (Rutstroemiaceae) and Hegermila Raitv. (Hyaloscyphaceae), were only observed as sexual morphs, but Neofabraea H.S. Jacks (Dermateaceae) and Articulospora Ingold (Helotiaceae) were observed as having asexual and sexual morphs (Chen et al. 2015, Wijayawardene et al. 2018, Wang et al. 2015a). In this study, we just observed the asexual morph of B. persicolor.

Based on ITS sequence data, B. persicolor is 88% similar to the genus Tetracladium De Wild. (T. marchalianum De Wild. as the type species), which was placed in the Helotiales and family incertae sedis. Moreover, Blastosporium shares some morphological features with Tetracladium as pale yellow and compact colonies and hyphae branched, septate and hyaline and both Blastosporium and Tetracladium sporulated abundantly on natural substrates (Sati et al. 2009, Wang et al. 2015b). However, B. persicolor is obviously distinct from the genus Tetracladium by the size and shape of conidia.

By molecular phylogeny analysis, Blastosporium belongs to the order Helotiales that currently contains 27 families (Wijayawardene et al. 2018). Moreover, members of the Helotiales cover a broad range of niches, such as plant pathogens, endophytes and aquatic hyphomycetes. Blastosporium persicolor was discovered from mildewed tobacco; therefore, it may be a plant pathogen.

Acknowledgements

This work was financed by the National Natural Science Foundation Program of PR China (31570023, 31770026). We are grateful to two reviewers for critically reviewing the manuscript and for providing helpful suggestions to improve this paper.

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