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Research Article
Micromelanconis kaihuiae gen. et sp. nov., a new diaporthalean fungus from Chinese chestnut branches in southern China
expand article infoNing Jiang, Qin Yang§, Xin-Lei Fan, Cheng-Ming Tian
‡ Beijing Forestry University, Beijing, China
§ Central South University of Forestry and Technology, Changsha, China
Open Access

Abstract

Melanconis-like fungi are distributed in several families of Diaporthales, mainly Juglanconidaceae, Melanconidaceae, Melanconiellaceae and Pseudomelanconidaceae. A new Melanconis-like genus of Pseudomelanconidaceae was discovered on branches of Chinese chestnut (Castanea mollissima) in southern China, which was confirmed by both morphology and phylogenetic analysis of combined ITS, LSU, tef1a and rpb2 sequences. The new genus Micromelanconis is characterized by two types of conidia from natural substrate and manual media of PDA, respectively. Conidia from Chinese chestnut branches are pale brown, ellipsoid, multiguttulate, aseptate with hyaline sheath. While conidia from PDA plates are pale brown, long dumbbell-shaped, narrow at the middle and wide at both ends, multiguttulate, aseptate, and also with hyaline sheath. All Pseudomelanconidaceae species were only reported on tree branches in China until now. More interesting taxa may be discovered if detailed surveys on tree-inhabiting fungi are carried out in East Asia in the future.

Keywords

Castanea mollissima, Diaporthales, DNA phylogeny, Melanconis, systematics

Introduction

Diaporthales, a species-rich order within Sordariomycetes of Ascomycota, is characterized by perithecia with elongate beaks, often forming within stromatic tissues, deliquescent paraphyses, and asci that have a refractive apical annulus (Barr 1978; Rossman et al. 2007; Senanayake et al. 2017, 2018; Fan et al. 2018a; Jiang et al. 2020a). Species of this order inhabit a variety of substrates, including plants, soil, even living animal tissues (Barr 1978; Castlebury et al. 2002; Sogonov et al. 2008; Yang et al. 2020). Most of them are pathogens associated with plant diseases, and the rest are endophytes in healthy plants or saprobes on dead tissues (Crous et al. 2012a; Chen et al. 2016; Norphanphoun et al. 2018; Jiang et al. 2019d; Xavier et al. 2019; Zhu et al. 2020; Yang et al. 2021). Some diaporthalean fungi cause severe forest diseases, so gained attention in forest pathological studies in recent years. For example, Cryphonectria parasitica (Cryphonectriaceae) causes chestnut blight worldwide (Rigling and Prospero 2018; Jiang et al. 2019b); Cytospora chrysosperma (Cytosporaceae) causes common polar and willow cankers in China (Fan et al. 2020); Gnomoniopsis smithogilvyi (Gnomoniaceae) results in European chestnut fruit rot and branch canker (Shuttleworth et al. 2016; Shuttleworth and Guest 2017; Jiang and Tian 2019; Jiang et al. 2020b).

Diaporthales is well classified into families based on morphological and phylogenetic studies (Voglmayr and Jaklitsch 2014; Norphanphoun et al. 2016; Voglmayr et al. 2017; Fan et al. 2018a; Senanayake et al. 2018; Yang et al. 2018a), and up to 32 families were accepted in the order Diaporthales (Jiang et al. 2021). Specimens can be identified to specific level by morphological characters, such as transversely distoseptate brown conidia of Coryneum (Jiang et al. 2018b, 2019c; Senwanna et al. 2018); allantoid ascospores and conidia of Cytospora (Fan et al. 2020); two-guttulate fusiform conidia of Diaporthe-like taxa (Fan et al. 2018a; Yang et al. 2018a, b); stromatic tissues turning to purple in 3% KOH of Cryphonectriaceae species (Chen et al. 2013, 2018); dark acervular conidiomata with conspicuous central column of Melanconis-like taxa (Fan et al. 2016; Jaklitsch and Voglmayr 2020).

Melanconis-like taxa are distributed in several families of Diaporthales, mainly Juglanconidaceae, Melanconidaceae, Melanconiellaceae and Pseudomelanconidaceae, which are four morphologically similar clades in distinct phylogenetic clades within this order (Fan et al. 2018b). Species of these four families are usually discovered on branches of Betulaceae, Juglandaceae and Fagaceae, but they are not strong pathogens (Wehmeyer 1937; Du et al. 2017; Voglmayr et al. 2019).

Castanea, commonly known as chestnut trees, is a worldwide genus containing several economic species. Chinese chestnut (C. mollissima), is widely cultivated in most of the provinces in China. Previous studies have revealed that seven families (Coryneaceae, Cryphonectriaceae, Cytosporaceae, Diaporthaceae, Erythrogloeaceae, Gnomoniaceae and Pseudomelanconidaceae) of Diaporthales have been reported on branches of Castanea. Coryneum castaneicola, C. gigasporum and C. suttonii of Coryneaceae were reported on dead and diseased Castanea mollissima branches (Jiang et al. 2018b). Aurantiosacculus castaneae, Cryphonectria neoparasitica, C. parasitica and Endothia chinensis of Cryphonectriaceae were confirmed to be Castanea mollissima canker pathogens (Jiang et al. 2019b). Cytospora ceratospermopsis, C. kuanchengensis, C. leucostoma, C. myrtagena, C. schulzeri and C. xinglongensis of Cytosporaceae were reported to be associated with Castanea mollissima branch cankers (Jiang et al. 2020c). Diaporthe eres of Diaporthaceae was discovered on dead branches of Castanea mollissima in Beijing (Yang 2018). Dendrostoma aurorae, D. castaneae, D. castaneicola, D. chinense, D. parasiticum, D. shaanxiense and D. shandongense of Erythrogloeaceae were associated with Castanea mollissima stem, branch and twig cankers (Jiang et al. 2019a). Gnomoniopsis chinensis of Gnomoniaceae caused severe stem and branch cankers only in Hebei Province (Jiang and Tian 2019; Jiang et al. 2020b). Neopseudomelanconis castaneae of Pseudomelanconidaceae was discovered on Castanea mollissima branches in Shaanxi Province (Jiang et al. 2018a).

In the present study, investigations were conducted in Castanea mollissima plantations in Hunan Province of south China. Two Melanconis-like specimens were collected on a cultivated chestnut tree. The aim of the present study was to identify the fresh collections and confirm their phylogenetic positions.

Materials and methods

Collection, examination and isolation

The fresh specimens of diseased and dead chestnut branches were collected in a Castanea mollissima plantation in Hunan Province of south China. Morphological characteristics of the conidiomata were determined under a Nikon AZ100 dissecting stereomicroscope. More than 20 fruiting bodies were sectioned, and 50 conidia were selected randomly for measurement using a Leica compound microscope (LM, DM 2500). Isolates were obtained by removing a mucoid conidial mass from conidiomata, spreading the suspension onto the surface of 1.8% potato dextrose agar (PDA), and incubated at 25 °C for up to 24 h. Single germinating conidium was removed and plated onto fresh PDA plates. Cultural characteristics of isolates incubated on PDA in the dark at 25 °C were recorded, including the colony color and conidiomata structures. Specimens were deposited in the Museum of the Beijing Forestry University (BJFC). Axenic cultures were maintained in the China Forestry Culture Collection Centre (CFCC).

DNA extraction, PCR amplification and phylogenetic analyses

Genomic DNA was extracted from colonies grown on cellophane-covered PDA, using a cetyltrimethylammonium bromide (CTAB) method (Doyle and Doyle 1990). DNA was estimated by electrophoresis in 1% agarose gel and the quality was measured using the NanoDrop 2000 (Thermo Scientific, Waltham, MA, USA). Four partial loci, including the 5.8S nuclear ribosomal DNA gene with the two flanking internally transcribed spacer (ITS) regions, the large subunit of the nrDNA (LSU), and the translation elongation factor 1-alpha (tef1a) and DNA-directed RNA polymerase II second largest subunit (rpb2) genes, were amplified by the following primer pairs: ITS1 and ITS4 for ITS (White et al. 1990), LR0R and LR5 for LSU (Vilgalys and Hester 1990), EF1-728F and EF2 for tef1a (O’Donnell et al. 1998; Carbone and Kohn 1999), and RPB2-5F and fRPB2-7cR for rpb2 (Liu et al. 1999). The polymerase chain reaction (PCR) conditions were as follows: an initial denaturation step of 5 min at 94 °C, followed by 35 cycles of 30 s at 94 °C, 50 s at 48 °C (ITS, LSU) or 54 °C (tef1a) or 55 °C (rpb2), and 1 min at 72 °C, and a final elongation step of 7 min at 72 °C. PCR products were assayed via electrophoresis in 2% agarose gels. DNA sequencing was performed using an ABI PRISM 3730XL DNA Analyser with a BigDye Terminater Kit v.3.1 (Invitrogen, USA) at the Shanghai Invitrogen Biological Technology Company Limited (Beijing, China).

For phylogenetic reconstruction, newly-generated sequences of ITS, LSU, tef1a and rpb2 were initially subjected to BLAST search (BLASTn) in NCBI website (https://www.ncbi.nlm.nih.gov). Then species and their sequences from recently published articles were selected and listed in Table 1 (Crous et al. 2012b; Alvarez et al. 2016; Senanayake et al. 2017; Braun et al. 2018; Fan et al. 2018a; Jiang et al. 2020a; Wang et al. 2020). The sequence alignments of the four individual loci (ITS, LSU, tef1a and rpb2) were conducted using MAFFT 7 (http://mafft.cbrc.jp/alignment/server/index.html), manually edited in MEGA 7.0.21, and then assembled as a dataset of ITS-LSU-tef1a-rpb2 to infer the phylogenetic placement of our new isolates.

ML and Bayesian analysis were implemented on the CIPRES Science Gateway portal (https://www.phylo.org) using RAxML-HPC BlackBox 8.2.10 (Stamatakis 2014) and MrBayes 3.1.2 (Ronquist and Huelsenbeck 2003), respectively. For ML analyses, a GTR+GAMMA substitution model with 1000 bootstrap iterations was set. MrModeltest 2.3 was used to estimate the best nucleotide substitution model settings for each gene. Bayesian inference (BI) was performed based on the DNA data set from the results of the MrModeltest, using a Markov chain Monte Carlo (MCMC) algorithm in MrBayes 3.1.2. Two MCMC chains were run from random trees for 1000 million generations and stopped when the average standard deviation of split frequencies fell below 0.01. Trees were saved each 1000 generations. The first 25% of trees were discarded as the burn-in phase of each analysis, and the Bayesian posterior probabilities (BPPs) were calculated from the remaining trees. Phylogenetic trees were viewed with FigTree v.1.3.1 and processed by Adobe Illustrator CS5. The nucleotide sequence data of the new taxon have been deposited in GenBank (Table 1).

Table 1.

Details of the isolates included for molecular study used in this study.

Species Isolates GenBank accession numbers
ITS LSU tef1a rpb2
Apiognomonia errabunda AR 2813 DQ313525 NG027592 DQ313565 DQ862014
Apiosporopsis carpinea CBS 771.79 NA AF277130 NA NA
Apoharknessia insueta CBS 111377* JQ706083 AY720814 MN271820 NA
CBS 114575 MN172402 MN172370 MN271821 NA
Asterosporium asterospermum MFLU 15-3555 NA MF190062 NA NA
Auratiopycnidiella tristaniopsis CBS 132180* JQ685516 JQ685522 MN271825 NA
CPC 16371 MN172405 MN172374 MN271826 NA
Aurifilum marmelostoma CBS 124928* FJ890495 MH874934 MN271827 MN271788
Celoporthe eucalypti CBS 127190* HQ730837 HQ730863 HQ730850 MN271790
Celoporthe woodiana CBS 118785* DQ267131 MN172375 JQ824071 MN271791
Chiangraiomyces bauhiniae MFLUCC 17-1669 MF190119 MF190064 MF377598 MF377603
Coniella africana CBS 114133* AY339344 AY339293 KX833600 KX833421
Coniella eucalyptorum CBS 112640* AY339338 AY339290 KX833637 KX833452
Coniella fusiformis CBS 141596* KX833576 KX833397 KX833674 KX833481
Coniella javanica CBS 455.68* KX833583 KX833403 KX833683 KX833489
Coryneum gigasporum CFCC 52319* MH683565 MH683557 MH685737 MH685729
Coryneum umbonatum D201 MH674329 MH674329 MH674337 MH674333
Cryphonectria decipens CBS 129353 EU442655 MN172386 MN271845 MN271797
Cryptometrion aestuescens CBS 124007* GQ369457 MN172387 MN271851 MN271798
Cytospora chrysosperma CFCC 89982 KP281261 KP310805 KP310848 KU710952
Cytospora elaeagni CFCC 89633 KF765677 KF765693 KU710919 KU710956
Dendrostoma aurorae CFCC 52753* MH542498 MH542646 MH545447 MH545405
Dendrostoma castaneae CFCC 52745* MH542488 MH542644 MH545437 MH545395
Dendrostoma chinense CFCC 52755* MH542500 MH542648 MH545449 MH545407
Dendrostoma dispersum CFCC 52730* MH542467 MH542629 MH545416 MH545374
Dendrostoma mali CFCC 52102* MG682072 MG682012 MG682052 MG682032
Dendrostoma osmanthi CFCC 52106* MG682073 MG682013 MG682053 MG682033
Dendrostoma parasiticum CFCC 52762* MH542482 MH542638 MH545431 MH545389
Dendrostoma qinlingense CFCC 52732* MH542471 MH542633 MH545420 MH545378
Dendrostoma quercinum CFCC 52103* MG682077 MG682017 MG682057 MG682037
Dendrostoma quercus CFCC 52739* MH542476 MH542635 MH545425 MH545383
Dendrostoma shaanxiense CFCC 52741* MH542486 MH542642 MH545435 MH545393
Dendrostoma shandongense CFCC 52759* MH542504 MH542652 MH545453 MH545411
Diaporthosporella cercidicola CFCC 51994* KY852492 KY852515 MN271855 NA
Diaporthostoma machili CFCC 52100* MG682080 MG682020 MG682060 MG682040
CFCC 52101 MG682081 MG682021 MG682061 MG682041
Dwiroopa lythri CBS 109755* MN172410 MN172389 MN271859 MN271801
Dwiroopa punicae CBS 143163* MK510676 MK510686 NA MK510692
Foliocryphia eucalypti CBS 124779* GQ303276 GQ303307 MN271861 MN271802
Foliocryphia eucalyptorum CBS 142536* KY979772 KY979827 MN271862 MN271803
Gnomonia gnomon CBS 199.53 DQ491518 AF408361 EU221885 EU219295
Harknessia australiensis CBS 132119* JQ706085 JQ706211 MN271863 NA
Harknessia capensis CBS 111829* AY720719 AY720816 MN271864 NA
Harknessia ellipsoidea CBS 132121* JQ706087 JQ706213 MN271865 NA
Harknessia eucalypti CBS 342.97 AY720745 AF408363 MN271866 NA
Holocryphia eucalypti CBS 115842* MN172411 MN172391 MN271882 MN271804
Immersiporthe knoxdaviesiana CBS 132862* JQ862765 JQ862755 MN271886 MN271805
Juglanconis juglandina CBS 121083 KY427148 KY427148 KY427217 KY427198
Juglanconis oblonga MAFF 410216 KY427153 KY427153 KY427222 KY427203
Juglanconis pterocaryae MAFF 410079 KY427155 KY427155 KY427224 KY427205
Lamproconium desmazieri MFLUCC 15-0870 KX430134 KX430135 MF377591 MF377605
MFLUCC 15-0872 KX430138 KX430139 MF377593 MF377606
Macrohilum eucalypti CPC 10945 DQ195781 DQ195793 NA MN271809
CPC 19421 KR873244 KR873275 NA MN271810
Mastigosporella anisophylleae CBS 136421* KF779492 KF777221 MN271892 NA
Mastigosporella pigmentata COAD 2370* MG587929 MG587928 NA NA
Melanconiella ellisii BPI 878343 JQ926271 JQ926271 JQ926406 JQ926339
Melanconiella spodiaea MSH JQ926298 JQ926298 JQ926431 JQ926364
Melanconis betulae CFCC 50471 KT732952 KT732971 KT733001 KT732984
Melanconis itoana CFCC 50474 KT732955 KT732974 KT733004 KT732987
Melanconis stilbostoma CFCC 50475 KT732956 KT732975 KT733005 KT732988
Micromelanconis kaihuiae CFCC 54572* MW414473 MW414373 MW419880 MW419878
KH5-4 MW414474 MW414374 MW419881 MW419879
Nakataea oryzae CBS 243.76 KM484861 DQ341498 NA NA
Neopseudomelanconis castaneae CFCC 52787* MH469162 MH469164 NA NA
Phaeoappendicospora thailandensis MFLU 12-2131 MF190157 MF190102 NA NA
Prosopidicola albizziae CPC 27478 KX228274 KX228325 NA NA
Prosopidicola mexicana CBS 113529 AY720709 NA NA NA
Pseudomelanconis caryae CFCC 52110* MG682082 MG682022 MG682062 MG682042
Pseudoplagiostoma corymbiae CPC 14161 GU973510 GU973604 GU973540 NA
Pseudoplagiostoma oldii CBS 115722 GU973535 GU973610 GU973565 NA
Pseudoplagiostoma variabile CBS 113067 GU973536 GU973611 GU973566 NA
Pyricularia grisea Ina168 NA AB026819 NA NA
Pyrispora castaneae CFCC 54349 MW208108 MW208105 MW227340 MW218535
CFCC 54351 MW208110 MW208107 MW227342 MW218537
Sillia karstenii MFLU 16-2864 KY523482 KY523500 NA KY501636
Sirococcus tsugae CBS 119626 EU199203 EU199136 EF512534 EU199159
Stegonsporium acerophilum CBS 117025 EU039982 EU039993 EU040027 KF570173
Stilbospora longicornuta CBS 122529* KF570164 KF570164 KF570232 KF570194
Synnemasporella aculeans CFCC 52094 MG682086 MG682026 MG682066 MG682046
Synnemasporella toxicodendri CFCC 52097* MG682089 MG682029 MG682069 MG682049
Thailandiomyces bisetulosus BCC 00018 NA EF622230 NA NA
Tirisporella beccariana BCC 38312 NA JQ655449 NA NA
Tubakia seoraksanensis CBS 127490* MG591907 KP260499 MG592094 NA
Tubakia iowensis CBS 129012* MG591879 MG591971 MG592064 NA
Ursicollum fallax CBS 118663* DQ368755 EF392860 MN271897 MN271816

Results

The ITS, LSU, tef1a and rpb2, and combined data matrices contained 624, 867, 513, 865, and 2869 characters with gaps, respectively. The alignment comprised 92 strains, with Nakataea oryzae (CBS 243.76) and Pyricularia grisea (Ina168) from Magnaporthales as outgroup taxa. The ML analysis yielded a tree with a ln likelihood value of –45806.266577 and the following model parameters: alpha = 0.298226, Π(A) = 0.241173, Π(C) = 0.258552, Π(G) = 0.275145, and Π(T) = 0.225130. For BI analyses, the general time reversible model, additionally assuming a proportion of invariant sites with gamma-distributed substitution rates of the remaining sites (GTR+I+G), was determined to be the best for the ITS, LSU, and tef1a loci by MrModeltest, whereas the most appropriate model for the rpb2 locus was the Tamura-Nei model, additionally assuming a proportion of invariant sites with gamma-distributed substitution rates of the remaining sites (TrN+I+G). The phylogeny resulting from the RAxML maximum likelihood analysis of the combined gene sequence data is shown in Fig. 1. Overall, the topologies obtained from the different phylogenetic analyses were similar, and the best scoring RAxML tree is illustrated here. The bootstrap support values above 50% of maximum likelihood analysis (ML) and Bayesian posterior probability scores (≥0.90) are noted at the nodes.

The Diaporthales separates into 32 clades, representing 32 families, and the new isolates were clustered with a well-supported clade (ML/BI = 100/1) in Pseudomelanconidaceae. The two new isolates were different from any known genera in Pseudomelanconidaceae, and represented a new genus (Fig. 1).

Figure 1. 

Phylogram of Diaporthales from a maximum likelihood analysis based on combined ITS, LSU, tef1a and rpb2. Values above the branches indicate maximum likelihood bootstrap (left, ML BP ≥ 50%) and Bayesian probabilities (right, BI PP ≥ 0.90). The tree is rooted with Nakataea oryzae (CBS 243.76) and Pyricularia grisea (Ina168). New species proposed in the current study is in blue and the ex-type strains are marked with *.

Figure 1. 

Continued.

Taxonomy

Micromelanconis C.M. Tian & N. Jiang, gen. nov.

MycoBank No: 838927

Etymology

Name derived from micro- and the genus name Melanconis.

Type species

Micromelanconis kaihuiae C.M. Tian & N. Jiang.

Description

Sexual morph: not observed. Asexual morph: Conidiomata acervular, conspicuous, immersed in host bark to erumpent, covered by brown to blackish exuding conidial masses at maturity. Central column beneath the disc more or less conical. Conidiophores unbranched, aseptate, cylindrical, pale brown, smooth-walled. Conidiogenous cells annellidic, occasionally with distinct annellations and collarettes. Conidia hyaline when immature, becoming pale brown, ellipsoid, multiguttulate, aseptate, with hyaline sheath. Conidiomata formed on PDA after three weeks, randomly distributed, and black. Conidiophores unbranched, septate, cylindrical, pale brown, smooth-walled. Conidiogenous cells annellidic. Conidia pale brown, long dumbbell-shaped, narrow at the middle and wide at both ends, multiguttulate, aseptate, with hyaline sheath.

Notes

Micromelanconis is the third genus after Neopseudomelanconis and Pseudomelanconis in the family Pseudomelanconidaceae (Fig. 1). Micromelanconis is united in this family based on the Melanconis-like conidiomata, and pale brown conidia with conspicuous hyaline sheath. Micromelanconis produces two types of conidia from natural branches and manual media respectively, which differs from Neopseudomelanconis and Pseudomelanconis (Fan et al. 2018a; Jiang et al. 2018a). Additionally, Neopseudomelanconis is characterized by its septate conidia (Jiang et al. 2018a).

Micromelanconis kaihuiae C.M. Tian & N. Jiang, sp. nov.

MycoBank No: 838928
Figures 2, 3

Etymology

Named after Kaihui Yang, a Chinese heroine; Kaihui is also the name of the town where holotype was collected.

Figure 2. 

Morphology of Micromelanconis kaihuiae on branches of Castanea mollissima (BJFC-S1831) A, B habit of conidiomata on a branch C transverse section of conidiomata D longitudinal section through conidiomata E conidiogenous cells attached with conidia F, G conidia. Scale bars: 100 μm (C, D); 10 μm (E–G).

Description

Sexual morph: not observed. Asexual morph: Conidiomata acervular, 350–800 μm diam., conspicuous, immersed in host bark to erumpent, covered by brown to blackish exuding conidial masses at maturity. Central column beneath the disc more or less conical. Conidiophores unbranched, aseptate, cylindrical, pale brown, smooth-walled. Conidiogenous cells annellidic, occasionally with distinct annellations and collarettes, 12.4–47.1 × 1.2–3.8 μm. Conidia hyaline when immature, becoming pale brown, ellipsoid, multiguttulate, aseptate, 7.6–10.3 × 3.1–4.1 μm, L/W = 2–3.2, with hyaline sheath, 1 μm.

Figure 3. 

Morphology of Micromelanconis kaihuiae on the PDA plate (CFCC 54572) A colony on PDA B habit of conidiomata formed on PDA C, D conidiogenous cells attached with conidia E, F conidia. Scale bars: 10 μm (C–F).

Culture characters

Colony on PDA at 25 °C irregular, grey olivaceous, margin becoming diffuse, aerial hyphae short, dense, surface becoming imbricate, growth limited and ceasing after two weeks. Conidiomata formed after three weeks, randomly distributed, black. Conidiophores unbranched, septate, cylindrical, pale brown, smooth-walled. Conidiogenous cells annellidic, 9.1–18.5 × 2.5–5.3 μm. Conidia pale brown, long dumbbell-shaped, narrow at the middle and wide at both ends, multiguttulate, aseptate, 10.4–13.5 × 4–5 μm, L/W = 2.3–3.3, with hyaline sheath, 1.5 μm.

Specimens examined

China, Hunan Province, Changsha City, Changsha County, Kaihui Town, chestnut plantation, 40°24'32.16"N, 117°28'56.24"E, 262 m asl, on stems and branches of Castanea mollissima, Tian Chengming and Ning Jiang, 10 November 2020 (BJFC-S1831, holotype; ex-type culture, CFCC 54572 = KH5-3). Ibid. (BJFC-S1832, KH5-4).

Notes

Micromelanconis kaihuiae on Castanea mollissima (Fagaceae, Fagales) is phylogenetically close to Neopseudomelanconis castaneae on Castanea mollissima and Pseudomelanconis caryae on Carya cathayensis (Juglandaceae, Juglandales) (Fig. 1). All these three species are discovered on tree branches in China, and share similar morphological characters in having pale brown conidia with conspicuous hyaline sheath. Micromelanconis kaihuiae and Neopseudomelanconis castaneae even share the same host. However, they can be easily distinguished based on conidia shape, color and overall size of conidia (M. kaihuiae, pale brown, ellipsoid and aseptate conidia, 7.6–10.3 × 3.1–4.1 μm; pale brown, long dumbbell-shaped and aseptate conidia, 10.4–13.5 × 4–5 μm vs. N. castaneae, brown, ellipsoid to oblong and septate conidia, 18–21.5 × 4.8–7 μm vs. P. caryae, pale brown, ellipsoid to oblong and aseptate conidia, 12.5–16 × 4–5 μm) (Fan et al. 2018a; Jiang et al. 2018a). Furthermore, M. kaihuiae is separated from N. castaneae by 51/490 bp (10.4%) differences in ITS and 12/563 bp (2.1%) differences in LSU, and from P. caryae by 56/490 bp (11.4%) differences in ITS and 6/563 bp (1.1%) differences in LSU.

Key to Pseudomelanconidaceae genera and species

1 On Carya of Juglandaceae, conidia ellipsoid to oblong and aseptate Pseudomelanconis caryae
On Castanea of Fagaceae 2
2 Conidia aseptate Micromelanconis kaihuiae
Conidia septate Neopseudomelanconis castaneae

Discussion

Diaporthales is a well-studied order based on integrated approaches of morphology and phylogeny in recent years (Castlebury et al. 2002; Rossman et al. 2007; Voglmayr and Jaklitsch 2014; Alvarez et al. 2016; Senanayake et al. 2017, 2018; Voglmayr et al. 2017; Braun et al. 2018; Fan et al. 2018a; Jiang et al. 2020a). Thirty-two accepted families are monophyletic and supported by morphological characters; four of them contain Melanconis-like fungi, namely Juglanconidaceae, Melanconidaceae, Melanconiellaceae and Pseudomelanconidaceae (Fan et al. 2018a). The Melanconis-like fungi were similar in their asexual morph, but well-separated in the phylogeny and their hosts (Voglmayr et al. 2012, 2017, 2019; Fan et al. 2018a, b; Jaklitsch and Voglmayr 2020). In the present study, a new genus and species were clustered in the family Pseudomelanconidaceae (Fig. 1), and differed from the other Melanconis-like genera by its long dumbbell-shaped conidia formed on PDA plates.

Hosts are useful taxonomic information in some families of Diaporthales, such as Coryneaceae, Cryphonectriaceae, Erythrogloeaceae and Gnomoniaceae (Voglmayr et al. 2012; Jaklitsch and Voglmayr 2019; Roux et al. 2020; Wang et al. 2020; Yang et al. 2020). Hosts are important to separate Melanconis-like genera, Juglanconis inhabit Juglans and Pterocarya of Juglandaceae, Melanconiella and Melanconis occur only on the plant family Betulaceae (Voglmayr et al. 2012, 2017, 2019; Fan et al. 2018b; Jaklitsch and Voglmayr 2020). Melanconis species are discovered only on Alnus and Betula, while Melanconiella occurs in the subfamily Coryloideae with the exception of M. betulae and M. decorahensis on Betula (Voglmayr et al. 2012; Du et al. 2017; Fan et al. 2018a). Species of Pseudomelanconidaceae inhabit Carya of Juglandaceae, and Castanea of Fagaceae (Fan et al. 2018a; Jiang et al. 2021). More interesting Melanconis-like may be revealed by more detailed surveys on tree-inhabiting fungi in the future.

Acknowledgements

This study is financed by the National Natural Science Foundation of China (Project No.: 31670647). We are grateful to Chungen Piao and Minwei Guo (China Forestry Culture Collection Center, Chinese Academy of Forestry, Beijing) for support of strain preservation during this study.

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