A highly diverse fungal community associated with leaves of the mangrove plant Acanthus ilicifolius var. xiamenensis revealed by isolation and metabarcoding analyses

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Plant Biology

Introduction

Mangroves are tropical intertidal forest communities, situated at coastal areas from low to high salinities (Tomlinson, 1986). These communities host both terrestrial and marine fungi: terrestrial fungi, such as endophytic fungi, occur on the aerial parts of the plants, while marine fungi usually grow on the submerged/intertidal dead branches of the trees. Endophytic fungi inhabit plant organs for some time in their life cycle, and they can colonize internal plant tissues without causing apparent harm to the host (Petrini, 1991). Arnold (2007) revised the definition of endophytic fungi as ‘a polyphyletic group of highly diverse, primarily ascomycetous fungi, defined functionally by their occurrence within asymptomatic tissues of plants’.

For the last decade, various mangrove plants were examined for their endophytic fungal assemblages. The Ascomycota was dominant with many asexual species while the Basidiomycota was rare (De Souza Sebastianes et al., 2013; Zhou et al., 2018). Pang et al. (2008) summarized the dominant endophytic fungi of various mangrove plant species and there were several common taxa: Sporormiella minima, Guignardia/Phyllosticta spp., Phoma spp., Diaporthe/Phomopsis spp., Cladosporium spp., Acremonium spp. and Collectotrichum spp. Xylaria spp. and Pestalotiopsis spp. were also common (Suryanarayanan & Kumaresan, 2000; Chaeprasert et al., 2010; Xing & Guo, 2011; De Souza Sebastianes et al., 2013). Abundance and richness of endophytic fungi of mangrove plants are dependent on mangrove plant species and also their tissue types, i.e., stem, leaf or root (Xing et al., 2011; Zhou et al., 2018). Avicennia germinans was found to support the lowest diversity of endophytic fungi compared with Laguncularia racemosa and Rhizophora mangle, and it was concluded to be the effect of salt excreted from leaves of A. germinans, which inhibits spore germination (Gilbert, Mejía-Chang & Rojas, 2002). De Souza Sebastianes et al. (2013) studied endophytic fungi in branches and leaves of Rhizophora mangle, Avicennia schaueriana and Laguncularia racemosa and found that branches had a higher frequency of colonization and diversity than leaves. A higher number of isolates and species richness were also obtained from stems than roots in four species of Rhizophoraceae mangrove plants (Xing & Guo, 2011). Roots of mangrove plants are inhabited with terrestrial, freshwater and marine fungi (Ananda & Sridhar, 2002). Using high throughput sequencing techniques, Arfi et al. (2012) found that different fungal classes/orders were dominant in Avicennia marina and Rhizophora stylosa and between aerial and intertidal parts of the trees. Some endophytic fungi are host-specific and their diversity is seasonally varied (Suryanarayanan, Kumaresan & Johnson, 1998; Costa, Maia & Cavalcanti, 2012). Diversity of endophytic fungi increased with leaf age and some fungi may switch from an endophytic lifestyle to a saprobic one after leaf fall (Kumaresan & Suryanarayanan, 2002).

Acanthus ilicifolius var. xiamenensis is a mangrove plant distributed along the coast of southern China. The only distribution of A. ilicifolius var. xiamenensis in Taiwan is at Liuyu Township, Kinmen County with two small patches. However, their survival is under threat due to construction work for urban development. Previous studies on endophytic fungal assemblages associated with A. ilicifolius found that Colletotrichum spp. and Phomopsis spp. were the dominant species (Suryanarayanan & Kumaresan, 2000; Chaeprasert et al., 2010). This study investigates the cultural diversity of endophytic fungi of surface-sterilized healthy leaves of A. ilicifolius var. xiamenensis and the diversity of fungi of the same leaves using Illumina MiSeq sequencing.

Materials and Methods

Collection of samples

The mangrove plants Aegiceras corniculatum, Acanthus ilicifolius var. xiamenensis and Kandelia obovata are present at Lieyu Township, Kinmen County, Taiwan. A. ilicifolius var. xiamenensis is the only mangrove plant growing at the sampling site at Lieyu Township and it represents the only distribution in Taiwan (Fig. 1). The characteristics of A. ilicifolius var. xiamenensis are shown in Fig. 2. Healthy leaves (i.e., for isolation of endophytic over saprobic/pathogenic fungi) were collected on 16 January (60 leaves) and 11 July (35 leaves) 2014, placed in a cool box and transported to the laboratory at National Taiwan Ocean University for immediate fungal isolation.

Sampling site.

Figure 1: Sampling site.

(A) Location of Kinmen County (box), Taiwan; (B) distribution of Acanthus ilicifolius var. xiamenensis at Lieyu Township, where the samples were collected (star).

Fungal isolation

Leaves were washed with tap water to remove surface dirt. Four discs (6 mm in diameter) were cut out from each leaf, surface-sterilized by immersing in 70% ethanol for 10 s and 4% sodium hypochlorite solution for 30 s, washed twice in sterile distilled water, and plated on 2% malt extract freshwater agar (MEAF, BD Bacto™; BD Biosciences, Sparks, MD, USA), supplemented with 0.5 g/L each of streptomycin sulfate (Sigma-Aldrich, MO, USA) and Penicillin G (Sigma-Aldrich, MO, USA). The inoculated plates were incubated at 25 °C and checked daily to observe fungal growth from the leaf discs for 1 month. Hyphal tips of different mycelial morphotypes from each plate (i.e., from the same leaf) were isolated and subcultured onto fresh MEAF. All cultures were kept at National Taiwan Ocean University.

Morphology ofAcanthus ilicifolius var. xiamenensis.

Figure 2: Morphology ofAcanthus ilicifolius var. xiamenensis.

(A) Trees, (B) healthy leaves, (C) flowers, and (D) fruits surrounded by unhealthy leaves.

Identification of fungal isolates

All isolated cultures were grouped into different colony morphologies, and identified by comparing their ITS sequences with those deposited in the National Center for Biotechnology Information (NCBI). Mycelia for each morphotype were ground into fine powder in liquid nitrogen using a mortar and pestle. Genomic DNA was extracted using the DNeasy Plant DNA Extraction Kit (Qiagen, Germantown, MD, USA) according to the manufacturer’s instructions. ITS was amplified using the primer pairs ITS1 (or ITS5)/ITS4 (White et al., 1990). PCR reactions were performed in a 25 µL volume containing ca. 20 ng DNA, 0.2 µM of each primer, 0.2 mM of each dNTP, 2.5 mM MgCl2 and 1.25 U of Taq Polymerase (Invitrogen, Sao Paulo, Brazil). The amplification cycle consisted of an initial denaturation step of 95 °C for 2 min followed by 35 cycles of (a) denaturation (95 °C for 1 min), (b) annealing (54 °C for 1 min) and (c) elongation (72 °C for 1.5 min) and a final 10 min elongation step at 72 °C. The PCR products were analysed by agarose gel electrophoresis and sent to Genomics BioSci & Tech (New Taipei City, Taiwan) for sequencing. The sequences returned were checked for ambiguity and the forward/reverse strands were assembled in MEGA7 (Kumar, Stecher & Tamura, 2016). The assembled sequences were submitted to NCBI for a nucleotide BLAST search. The ITS sequences of the fungal isolates were deposited in NCBI with the accession numbers given in Table 1.

Metabarcoding

Seventeen leaves used for the isolation described above were freeze-dried. Total genomic DNA was extracted using QIAGEN DNeasy Plant Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions. A nested PCR approach was used to amplify a region of ITS spanning from 18S to 5.8S rDNA. The first set of primers was NSA3 (5′-AAACTCTGTCGTGCTGGGGATA-3′)/NLC2 (5′-GAGCTGCATTCCCAAACAACTC-3′) (Martin & Rygiewicz, 2005) and the second set was ITS1-F_KYO1 (5′-CTHGGTCATTTAGAGGAASTAA-3′)/ITS2 (5′-GCTGCGTTCTTCATCGATGC-3′) (White et al., 1990; Toju et al., 2012). Adapters were added to the 5′ end of the primers ITS1-F_KYO1 and ITS2. PCR amplification cycle with NSA3/NLC2 primers consisted of an initial denaturation step of 94 °C for 5 min, followed by 35 cycles of 94 °C for 30 s, 55 °C for 30 s and 72 °C for 30 s, and a final 5-min elongation step at 72 °C. For ITS1-F_KYO1/ITS2, the amplification consisted of an initial denaturation step of 95 °C for 10 min, followed by 35 cycles of 95 °C for 30 s, 55 °C for 30 s and 72 °C for 30 s, and a final 72 °C for 7 min. The PCR products were analyzed by agarose gel electrophoresis. For each leaf, five successful PCR products were pooled and purified using EasyPureTM PCR Clean up/Gel Extraction Kit (Bioman, New Taipei City, Taiwan) according to manufacturer’s instructions. The purified product was shipped to Genomics (Taipei, Taiwan) for Illumina MiSeq sequencing.

Table 1:
Fungi isolated from surface-sterilized leaves of Acanthus ilicifolius var. xiamenensis in summer and winter sampling.
Identity was based on BLAST searches in NCBI and percentage of occurrence of fungi was calculated based on number of isolates.
Isolate number (NTOU) (accession number) Sequence length (bp) Phylum Class Order Family Taxa Maximum score Coverage(%) Similarity(%) Matched sequence(s) Occurrence (%)
Winter Summer Total
4398 (MK448262) 529 Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Acidiella uranophila 832 100 95 JQ904602 0.96 0.00 0.49
4330 (MK432953), 4899 (MK432954), 4902 (MK432955), 4904 (MK432956) 485–544 Ascomycota Dothideomycetes Pleosporales Pleosporaceae Alternaria alternata 896–1005 100 100 LC317410, MF422130 1.92 7.07 4.43
4336 (MK448263), 4368 (same colony morphology as 4336) 543 Ascomycota Dothideomycetes Pleosporales Pleosporaceae Alternaria sp. 1003 100 100 KY190102 7.69 0.00 3.94
4350 (MK448264) 556 Ascomycota Dothideomycetes Dothideales Dothioraceae Aureobasidium pullulans 1027 100 100 LC277149, LC277150 1.92 0.00 0.99
4909 (MK432957) 549 Ascomycota Dothideomycetes Dothideales Dothioraceae Aureobasidium sp. 1014 100 100 KF367567 0.00 1.01 0.49
4875 (MK448265) 557 Ascomycota Dothideomycetes Botryosphaeriales Botryosphaeriaceae Botryosphaeria dothidea 1029 100 100 KU686880 0.00 3.03 1.48
4340 (MK448266) 527 Ascomycota Dothideomycetes Capnodiales Cladosporiaceae Cladosporium dominicanum 974 100 100 MF472969, MF472970 1.92 0.00 0.99
4352 (MK432958), 4883 (MK432959) 524–525 Ascomycota Dothideomycetes Capnodiales Cladosporiaceae Cladosporium sp. 968–970 100 100 MG701131, MG572462 0.96 4.04 2.46
4372 (MK448279), 4386 (MK448280) 474–492 Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum boninense 837–876 100 99 FJ981604 1.92 0.00 0.99
4358 (MK448267), 4402 (MK448268) 567 Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum hippeastri 1001–1011 99 99 KR183779 4.81 0.00 2.46
4370 (MK432992), 4895 (MK432993), 4908 (MK432988) 515–567 Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum sp. 1 952–1048 100 100 MF076596, JN715846 2.88 9.09 5.91
4326 (MK448269), 4378 (MK448281), 4390 (MK448282) 536–553 Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum sp. 2 972–1003 100 99 HM357614 3.85 0.00 1.97
4324 (MK432994), 4356 (MK432995), 4364 (MK432989), 4903 (MK432996) 533–549 Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum sp. 3 985–1013 100 99–100 KX620331, KX620330, KY820893 7.69 1.01 4.43
4346 (MK432960), 4362 (MK432961), 4872 (MK432962), 4889 (MK432963) 490–533 Ascomycota Dothideomycetes Pleosporales Corynesporascaceae Corynespora cassiicola 898–985 99–100 99–100 FJ852578, KF266787, HM535404 5.77 8.08 6.90
4905 (MK448270), 4907 (MK448271) 546 Ascomycota Sordariomycetes Xylariales Hypoxylaceae Daldinia eschscholtzii 1003–1009 100 99–100 KY792621 0.00 4.04 1.97
4380 (MK432964), 4869 (same colony morphology as 4380), 4884 (MK432965), 4920 (MK432966) 550 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Diaporthe endophytica 1011–1016 100 99–100 NR_111847 0.96 10.10 5.42
4886 (MK448272) 551 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Diaporthe longicolla 1016 99 100 JQ754023 0.00 2.02 0.99
4382 (MK448253) 552 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Diaporthe perseae 974 100 98.55 KC343173 0.96 0.00 0.49
4376 (MK448273), 4915 (MK448274) 550–551 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Diaporthe phaseolorum 1002–1011 100 99 LN828206, KT964565 5.77 1.01 3.45
4334 (MK432967), 4354 (MK432968), 4400 (same colony morphology as 4334), 4404 (same colony morphology as 4334), 4878 (MK432998) 519 Ascomycota Dothideomycetes Pleosporales Didymellaceae Didymella sp. 948 100 99 HM012812 5.77 2.02 3.94
4901 (MK448275) 533 Ascomycota Dothideomycetes Dothideales Dothioraceae Dothioraceae sp. 894 99 97 KU892278 0.00 1.01 0.49
4410 (MK448276) 544 Ascomycota Dothideomycetes Pleosporales Pleosporaceae Drechslera dematioidea 1005 100 100 KY788112 10.58 0.00 5.42
4870 (MK448277), 4873 (MK448278), 4879 (MK448283), 4885 (MK448284), 4896 (MK448285), 4898 (MK448286) 467–518 Ascomycota Sordariomycetes Hypocreales Nectriaceae Fusarium oxysporum 863–957 100 100 MG727665, MG722826 0.00 13.13 6.40
4866 (MK432970), 4876 (MK432971), 4877 (MK432972) 488–532 Ascomycota Sordariomycetes Hypocreales Nectriaceae Fusarium sp. 902–983 100 100 MG562501, MG274294 0.00 8.08 3.94
4318 (MK432973), 4332 (MK432974), 4388 (MK432975), 4871 (MK432976), 4874 (MK432977) 587–613 Ascomycota Dothideomycetes Botryosphaeriales Botryosphaeriaceae Guignardia sp. 1085–1133 100 100 JQ341114, MF170677, LN828209, JN791605 5.77 7.07 6.40
4320 (MK432978), 4396 (MK432979) 432–523 Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Hortaea werneckii 798–966 100 100 GQ334389, KY434149 3.85 0.00 1.97
4348 (MK448249) 525 Ascomycota Sordariomycetes Xylariales Apiosporaceae Nigrospora sphaerica 970 100 100 MH028054, MG669225 3.85 0.00 1.97
4868 (MK432980) 720 Ascomycota Sordariomycetes Xylariales Xylariaceae Nodulisporium sp. 1297 100 99 KR016438 0.00 2.02 0.99
4408 (MK448250) 510 Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Parastagonospora phoenicicola 846 100 97 KY173428 1.92 0.00 0.99
4914 (MK432981) 579 Ascomycota Sordariomycetes Amphisphaeriales Pestalotiopsidaceae Pestalotiopsis microspora 1070 100 100 KX755255 0.00 1.01 0.49
4394 (MK448260) 550 Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Phaeophleospora eucalypticola 1016 100 100 NR_145123 0.96 0.00 0.49
4906 (MK432982) 618 Basidiomycota Agaricomycetes Polyporales Phanerochaetaceae Phanerina mellea 1136 100 99 KX752602 0.00 1.01 0.49
4917 (MK440618) 670 Basidiomycota Agaricomycetes Hymenochaetales Hymenochaetaceae Phellinus noxius 1218 99 99 KF233592 0.00 2.02 0.99
4406 (MK448251) 508 Ascomycota Dothideomycetes Pleosporales Phoma sp. 1 939 100 100 KY780194 1.92 0.00 0.99
4338 (MK432990), 4366 (MK432991) 465 Ascomycota Dothideomycetes Pleosporales Phoma sp. 2 859 100 100 JX157864 2.88 0.00 1.48
4384 (MK448252) 551 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Phomopsis asparagi 1007 100 99 JQ613999 0.96 0.00 0.49
4918 (MK432997) 554 Ascomycota Sordariomycetes Diaporthales Diaporthaceae Phomopsis sp. 883 97 96 AB245060 0.00 3.03 1.48
4893 (MK432983) 517 Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Pseudocercospora nymphaeacea 955 100 100 KY304491 0.00 1.01 0.49
4374 (MK448254) 518 Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Pseudocercospora sp. 957 100 100 KP896027 1.92 0.00 0.99
4892 (MK448255) 532 Ascomycota Dothideomycetes Capnodiales Dissoconiaceae Ramichloridium punctatum 839 100 95 MF319925 0.00 2.02 0.99
4890 (MK448256), 4891 (MK448261) 518–569 Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Septoriella hubertusii 920–970 95–100 99 KT827267 0.00 2.02 0.99
4328 (MK448257) 603 Ascomycota Dothideomycetes Pleosporales Lentitheciaceae Setoseptoria arundinacea 1075 97 99 LC014594 0.96 0.00 0.49
4360 (MK448258) 518 Ascomycota Dothideomycetes Pleosporales Stagonosporopsis cucurbitacearum 957 100 100 KU059901, AB714985, AB714984 0.96 0.00 0.49
4392 (MK448259) 537 Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Teratosphaeria capensis 782 100 93 JN712501 4.81 0.00 2.46
4916 (MK432984) 593 Basidiomycota Agaricomycetes Polyporales Polyporaceae Tinctoporellus epimiltinus 1085 100 99 KY948722 0.00 2.02 0.99
4900 (MK432985) 564 Ascomycota Sordariomycetes Xylariales Xylariaceae Xylaria sp. 1040 99 100 JQ388255 0.00 2.02 0.99
4322 (MK432986), 4344 (MK432987) 460–513 Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Zasmidium citri 845–937 100 99 GU066616 2.88 0.00 1.48
DOI: 10.7717/peerj.7293/table-1

The raw sequences were filtered with a phred score ≥Q29 (a base call accuracy of ≥99.87%). The raw reads were paired into single reads and adaptors, primers and barcode sequences were removed using the QIIME script “split_library.py” (Caporaso et al., 2010). Clustering was performed using uclust v1.2.22q (Edgar, 2010) in QIIME 1.9.0 (Caporaso et al., 2010). The reads were processed with UCHIME (Edgar et al., 2011) to reject chimeric sequences. Picking of Operation Taxonomic Units (OTUs) and taxonomic assignments were performed with an open-reference OTU picking approach against the UNITE database in QIIME 1.9.0 (Caporaso et al., 2010). A similarity threshold of 97% was adopted. Taxonomic assignment of representative OTUs was run at a 0.97 confidence threshold against the UNITE ITS1 database with UNITE 7.2 reference OTU database (“UNITE+INSD” dataset) using the assignTaxonomy method (Kõljalg et al., 2013).

Statistical analysis

Total number of isolates (total abundance, N), Richness (total number of taxa in the community, S), Species Richness (Margalef), Shannon–Wiener Diversity Index, Pielou’s Evenness and Simpson Diversity Indices (Simpson’s Index, Simpson’s Index of Diversity, Simpson’s Reciprocal Index) were calculated in Microsoft Excel by first computing the variables of the equations and then using the math operators to calculate the different indices.

Rarefaction and extrapolation sampling curves were computed and plotted to estimate sample completeness (sample coverage) in R package iNEXT (iNterpolation/EXTrapolation) with the 95% lower and upper confidence limits for the isolation and metabarcoding data (Hsieh, Ma & Chao, 2016). A principle component analysis (PCA) was calculated by the R software using the R function prcomp() (R Core Team, 2013).

Results

Diversity of culturable fungi

A total of 203 isolates were cultured from leaves of Acanthus ilicifolius var. xiamenensis collected in January and July 2014 at Kinmen Township, Taiwan and ITS of the representative isolate for each morphotype was sequenced (Tables 12). The fungi were identified down to species level when the BLAST search results had a high percentage coverage and identity in NCBI; otherwise, they were given an identity at the genus/family level.

A total of 104 and 99 isolates were cultured from the winter (January) and summer (July) samples, representing 30 and 26 fungal species, respectively (Tables 12). Nine species were common between the two sampling times, therefore, 47 different fungal species were isolated from leaves of A. ilicifolius var. xiamenensis. The higher percentage of occurrence (Table 1) in the winter samples included Drechslera dematioidea (10.58%), Colletotrichum sp. 3 (7.69%) and Alternaria sp. (7.69%); and in the summer samples, Fusarium oxysporum (13.13%), Diaporthe endophytica (10.10%), Colletotrichum sp. 1 (9.09%), Fusarium sp. (8.08%), Corynespora cassiicola (8.08%), Guignardia sp. (7.07%) and Alternaria alternata (7.07%). Overall, C. cassiicola (6.90%), F. oxysporum (6.40%), Guignardia sp. (6.40%), Colletotrichum sp. 1 (5.91%), D. endophytica (5.42%) and D. dematioidea (5.42%) had the highest percentage of occurrence.

Diversity indices were calculated for the fungal communities in the winter and summer samples (Table 2). The fungal community in the winter samples had a higher species richness of 6.24 (Margalef) and a higher diversity of 3.15 (Shannon–Wiener Diversity Index) than that in the summer samples (5.44 and 2.92, respectively). The Margalef and Shannon–Wiener Diversity indices with the data combining the two seasons were 8.66 and 3.83, respectively. The rarefaction and extrapolation analysis suggested that species diversity was projected to be higher in the winter samples than in the summer samples but both samples did not reach species saturation (Fig. 3A).

Table 2:
Diversity indices of fungi associated with leaves of Acanthus ilicifolius var. xiamenensis using culture and metabarcoding analysis.
Culture Metabarcoding analysis
Winter Summer Total Winter Summer Total
Total No. of isolates/reads (Total Abundance), N 104 99 203 314692 458993 773685
Richness (Total number of Taxa in the community), S 30 26 47 96 70 111
Species Richness (Margalef): d = (S−1)/ln(N) 6.24 5.44 8.66 7.50 5.29 8.11
Shannon-Wiener Diversity Index: H′= −Σ[Pi ln(Pi)] 3.15 2.92 3.83 1.98 2.09 2.28
Pielou’s Evenness: J′= H′/ln(S) 0.93 0.90 0.99 0.44 0.49 0.49
Simpson Diversity Indices:
Simpson’s Index: D = Σ(Pi2) 0.05 0.07 0.29 0.29 0.23 0.18
Simpson’s Index of Diversity: 1−D = 1−Σ(Pi2) 0.95 0.93 0.71 0.72 0.78 0.82
Simpson’s Reciprocal Index: 1/D 19.52 14.74 3.47 3.51 4.45 5.60
DOI: 10.7717/peerj.7293/table-2

Figures 4A4C show the taxonomic composition of the cultured fungi at different taxonomic levels. In the winter (January 2014), only Ascomycota was isolated with no Basidiomycota; in the summer, Basidiomycota had a ∼5% occurrence (Fig. 4A). At the class level, Dothideomycetes and Sordariomycetes were the dominant classes in both seasons and Agaricomycetes was only isolated from the summer samples (Fig. 4B). At the ordinal level, the richness of fungi in summer was higher than that in winter. Seven orders Botryosphaeriales, Capnodiales, Diaporthales, Dothideales, Glomerellales, Pleosporales and Xylariales were common between the sampling times but varying in abundance (Fig. 4C). Amphisphaeriales and Hypocreales were not isolated in winter.

Sample-size-based rarefaction and extrapolation sampling curves.

Figure 3: Sample-size-based rarefaction and extrapolation sampling curves.

(A) Isolation and (B) metabarcoding studies of endophytic fungi associated with Acanthus ilicifolius var. xiamenensis.
Percentage of occurrence of fungi associated with leaves of Acanthus ilicifolius. var. xiamenensis.

Figure 4: Percentage of occurrence of fungi associated with leaves of Acanthus ilicifolius. var. xiamenensis.

Isolation method: (A) phylum, (B) class, and (C) order classification; metabarcoding analysis: (D) phylum, (E) class, and (F) order classification; both isolation and metabarcoding approaches: (G) phylum, (H) class, and (I) order classification.

Metabarcoding analysis

Seventeen samples (leaves) were analyzed by the metabarcoding analysis: 10 for the winter and 7 for the summer samples. A total of 773685 reads were obtained after QIIME analysis, including 314692 reads from the winter samples ranging from 2169 to 54606 reads, and 458993 reads from the summer samples ranging from 39151 to 93295 reads (Table 2). From the set of 17 samples, a total of 111 OTUs were identified, from which 86 could be referred to the generic level and 25 to the family level or above, including 96 OTUs (76 OTUs identified at the genus level) from the winter and 70 OTUs (55 OTUs identified at the genus level) from the summer samples (Table 3). Fifty-five OTUs (41 OTUs identified at the genus level) were common between the two seasons.

Figures 4D4F shows the proportions of the different taxa at the phylum, class and order levels. Both Ascomycota and Basidiomycota were recovered at proportions of 52.5% (percentage of occurrence based on read number) and 44.0% from the summer and 83.5% and 11.8% from the winter samples, respectively, with a higher proportion of basidiomycetous sequences in the summer samples (Fig. 4D). Overall, Ascomycota (65.1%) was dominant over Basidiomycota (30.9%).

At the class level, 11 different fungal classes were obtained from both the winter and summer samples (Fig. 4E). Seven classes were common between the samples: Agaricomycetes, Cystobasidiomycetes, Dothideomycetes, Eurotiomycetes, Microbotryomycetes, Sordariomycetes and Tremellomycetes. Dothideomycetes was the dominant class in both winter and summer samples (32.6% and 40.4%, respectively). Other classes only constituted less than 2% of the sequences, excluding those only referred to the phylum level (‘Others’). Exobasidiomycetes and Geminibasidiomycetes were only recovered from the winter samples and likewise, Malasseziomycetes and Saccharomycetes in the summer samples. The proportion of the different major classes overall was similar to that of the individual winter and summer samples.

Twenty-two and nineteen different fungal orders were identified in the winter and summer samples, respectively (Fig. 4F). Agaricales, Botryosphaeriales, Capnodiales, Chaetothyriales, Diaporthales, Dothideales, Erythrobasidiales, Eurotiales, Glomerellales, Hypocreales, Pleosporales, Polyporales, Russulales, Sporidiobolales, Tremellales and Xylariales were recovered from both samples but varying in abundance, excluding the sequences only identified above the order level (‘Others’). The dominant orders in the winter samples were Capnodiales (22.2%), Pleosporales (9.1%) and Tremellales (1.9%). Capnodiales (21.8%) was also the most dominant order in the summer samples, followed by Dothideales (14.5%) and Pleosporales (3.8%). Exobasidiales, Geminibasidiales, Golubeviales, Microascales and Venturiales were only found in the winter samples and Malasseziales and Saccharomycetales in the summer samples; these orders exclusive to their respective sample type only constituted a low sequence abundance (<0.1%). Combining the data from the two seasons, the dominant orders were Capnodiales (22.0%), Dothideales (8.8%) and Pleosporales (5.9%).

Table 3:
Fungal diversity associated with leaves of Acanthus ilicifolius var. xiamenensis in summer and winter samples recovered from metabarcoding analysis.
Percentage of occurrence of fungi was calculated based on number of reads.
Phylum Class Order Family Taxon % Occurrence
Winter Summer Total
Ascomycota Sordariomycetes Hypocreales Incertae sedis Acremonium polychromum 0.040 0.031 0.035
Basidiomycota Agaricomycetes Agaricales Agaricales 0.020 0.023 0.022
Basidiomycota Agaricomycetes Agaricomycetes 0.166 0.136 0.148
Ascomycota Dothideomycetes Pleosporales Pleosporaceae Alternaria sp. 3.463 0.122 1.481
Ascomycota Dothideomycetes Botryosphaeriales Aplosporellaceae Aplosporella yalgorensis 0.009 0.000 0.004
Ascomycota Sordariomycetes Xylariales Apiosporaceae Arthrinium sp. 0.007 0.002 0.004
Ascomycota Ascomycota 49.555 11.377 26.906
Ascomycota Eurotiomycetes Eurotiales Aspergillaceae Aspergillus penicillioides 0.008 0.000 0.003
Ascomycota Eurotiomycetes Eurotiales Aspergillaceae Aspergillus sp. 0.093 0.016 0.047
Ascomycota Dothideomycetes Dothideales Aureobasidiaceae Aureobasidium sp. 0.344 10.715 6.496
Ascomycota Dothideomycetes Dothideales Aureobasidiaceae Aureobasidium thailandense 0.000 0.064 0.038
Basidiomycota Basidiomycota 9.308 43.089 29.349
Basidiomycota Agaricomycetes Polyporales Meruliaceae Bjerkandera adusta 0.023 0.032 0.029
Basidiomycota Tremellomycetes Tremellales Bulleraceae Bullera unica 0.044 0.000 0.018
Ascomycota Dothideomycetes Capnodiales Capnodiales 15.762 5.083 9.427
Ascomycota Dothideomycetes Chaetothyriales Herpotrichiellaceae Capronia semi-immersa 0.036 0.035 0.035
Ascomycota Dothideomycetes Capnodiales Cladosporiaceae Cladosporium delicatulum 2.561 3.449 3.088
Ascomycota Dothideomycetes Capnodiales Cladosporiaceae Cladosporium sp. 0.189 7.901 4.764
Ascomycota Dothideomycetes Capnodiales Cladosporiaceae Cladosporium sphaerospermum 0.029 0.026 0.027
Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum brasiliense 0.011 0.063 0.042
Ascomycota Sordariomycetes Glomerellales Glomerellaceae Colletotrichum gloeosporioides 0.013 0.063 0.042
Ascomycota Dothideomycetes Pleosporales Coniothyriaceae Coniothyrium sidae 0.099 0.011 0.047
Basidiomycota Tremellomycetes Tremellales Tremellaceae Cryptococcus dimennae 0.073 0.000 0.030
Ascomycota Dothideomycetes Chaetothyriales Cyphellophoraceae Cyphellophora sessilis 0.086 0.000 0.035
Basidiomycota Tremellomycetes Tremellales Bulleribasidiaceae Derxomyces sp. 0.003 0.000 0.001
Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Devriesia sp. 0.051 0.000 0.021
Ascomycota Sordariomycetes Diaporthales Diaporthales sp. 1 0.332 0.157 0.228
Ascomycota Sordariomycetes Diaporthales Diaporthales sp. 2 0.099 0.167 0.139
Ascomycota Dothideomycetes Pleosporales Didymellaceae Didymella sp. 0.000 0.014 0.009
Ascomycota Dothideomycetes Pleosporales Didymosphaeriaceae Didymosphaeriaceae 1.017 0.016 0.423
Basidiomycota Tremellomycetes Tremellales Bulleribasidiaceae Dioszegia sp. 0.367 0.002 0.150
Basidiomycota Tremellomycetes Tremellales Bulleribasidiaceae Dioszegia takashimae 0.113 0.032 0.065
Ascomycota Dothideomycetes Dothideales Dothideales 0.000 0.491 0.291
Ascomycota Dothideomycetes Dothideomycetes 0.568 0.286 0.401
Basidiomycota Cystobasidiomycetes Erythrobasidiales Erythrobasidiaceae Erythrobasidium hasegawianum 0.022 0.003 0.011
Ascomycota Dothideomycetes Chaetothyriales Herpotrichiellaceae Exophiala sp. 0.003 0.000 0.001
Ascomycota Dothideomycetes Chaetothyriales Herpotrichiellaceae Exophiala xenobiotica 0.049 0.000 0.020
Fungi 4.735 3.577 4.048
Ascomycota Sordariomycetes Hypocreales Nectriaceae Fusarium solani 0.010 0.027 0.020
Ascomycota Sordariomycetes Hypocreales Nectriaceae Fusarium sp. 0.148 0.022 0.073
Basidiomycota Geminibasidiomycetes Geminibasidiales Geminibasidiaceae Geminibasidium sp. 0.004 0.000 0.002
Ascomycota Sordariomycetes Hypocreales Nectriaceae Gibberella intricans 0.106 0.019 0.054
Basidiomycota Exobasidiomycetes Golubeviales Golubeviaceae Golubevia pallescens 0.092 0.000 0.037
Ascomycota Sordariomycetes Microascales Halosphaeriaceae Halosphaeriaceae 0.010 0.000 0.004
Basidiomycota Tremellomycetes Tremellales Bulleribasidiaceae Hannaella oryzae 0.000 0.006 0.004
Ascomycota Dothideomycetes Dothideales Incertae sedis Hortaea werneckii 0.122 3.205 1.951
Ascomycota Sordariomycetes Hypocreales Hypocreales 0.005 0.000 0.002
Ascomycota Sordariomycetes Xylariales Xylariaceae Hypoxylon monticulosum 0.032 0.000 0.013
Ascomycota Dothideomycetes Pleosporales Lentitheciaceae Keissleriella yonaguniensis 0.409 0.003 0.168
Basidiomycota Tremellomycetes Tremellales Cuniculitremaceae Kockovaella sacchari 0.262 0.000 0.106
Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Leptospora rubella 0.518 0.000 0.211
Basidiomycota Malasseziomycetes Malasseziales Malasseziaceae Malassezia restricta 0.000 0.009 0.005
Ascomycota Dothideomycetes Pleosporales Trematosphaeriaceae Medicopsis romeroi 0.000 0.003 0.002
Basidiomycota Exobasidiomycetes Exobasidiales Brachybasidiaceae Meira argovae 0.037 0.000 0.015
Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Mycosphaerella etlingerae 0.008 0.000 0.003
Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Mycosphaerella sp. 0.078 0.000 0.032
Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Mycosphaerellaceae 2.517 0.556 1.354
Ascomycota Sordariomycetes Hypocreales Nectriaceae Nectriaceae 0.010 0.000 0.004
Ascomycota Sordariomycetes Xylariales Apiosporaceae Nigrospora oryzae 0.240 0.051 0.128
Ascomycota Dothideomycetes Venturiales Sympoventuriaceae Ochroconis musae 0.009 0.000 0.004
Basidiomycota Tremellomycetes Tremellales Rhynchogastremataceae Papiliotrema pseudoalba 0.840 0.212 0.467
Basidiomycota Tremellomycetes Tremellales Rhynchogastremataceae Papiliotrema sp. 0.000 0.194 0.115
Ascomycota Dothideomycetes Pleosporales Didymosphaeriaceae Paraconiothyrium sp. 0.032 0.000 0.013
Ascomycota Eurotiomycetes Eurotiales Aspergillaceae Penicillium sp. 0.000 0.013 0.007
Basidiomycota Agaricomycetes Russulales Peniophoraceae Peniophora sp. 0.002 0.004 0.003
Ascomycota Sordariomycetes Xylariales Sporocadaceae Pestalotiopsis rhododendri 0.005 0.000 0.002
Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Phaeophleospora hymenocallidicola 0.083 0.085 0.084
Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Phaeosphaeriaceae 0.000 0.031 0.018
Basidiomycota Agaricomycetes Polyporales Meruliaceae Phanerochaete tuberculata 0.028 0.024 0.025
Ascomycota Sordariomycetes Xylariales Incertae sedis Phialemoniopsis ocularis 0.007 0.000 0.003
Ascomycota Sordariomycetes Diaporthales Valsaceae Phomopsis sp. 0.012 0.042 0.030
Ascomycota Dothideomycetes Botryosphaeriales Phyllostictaceae Phyllosticta capitalensis 0.000 0.007 0.004
Ascomycota Sordariomycetes Glomerellales Plectosphaerellaceae Plectosphaerellaceae 0.014 0.000 0.006
Ascomycota Dothideomycetes Pleosporales Pleosporaceae Pleosporaceae 0.000 0.021 0.013
Ascomycota Dothideomycetes Pleosporales Pleosporales sp. 1 0.141 0.037 0.080
Ascomycota Dothideomycetes Pleosporales Pleosporales sp. 2 0.059 0.000 0.024
Ascomycota Dothideomycetes Pleosporales Sporomiaceae Preussia persica 0.091 0.082 0.085
Basidiomycota Agaricomycetes Agaricales Strophariaceae Psilocybe coprophila 0.003 0.000 0.001
Basidiomycota Agaricomycetes Agaricales Strophariaceae Psilocybe sp. 0.015 0.000 0.006
Ascomycota Dothideomycetes Pleosporales Cucurbitariaceae Pyrenochaetopsis leptospora 1.409 1.141 1.250
Ascomycota Dothideomycetes Pleosporales Cucurbitariaceae Pyrenochaetopsis sp. 1.146 0.146 0.552
Ascomycota Dothideomycetes Capnodiales Dissoconiaceae Ramichloridium luteum 0.048 0.000 0.020
Basidiomycota Microbotryomycetes Sporidiobolales Sporidiobolaceae Rhodotorula mucilaginosa 0.086 0.123 0.108
Basidiomycota Agaricomycetes Polyporales Meripilaceae Rigidoporus sp. 0.013 0.019 0.017
Ascomycota Dothideomycetes Pleosporales Thyridariaceae Roussoella solani 0.000 0.007 0.004
Basidiomycota Tremellomycetes Tremellales Trimorphomycetaceae Saitozyma flava 0.137 0.000 0.056
Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Sclerostagonospora ericae 0.033 0.124 0.087
Ascomycota Dothideomycetes Pleosporales Phaeosphaeriaceae Sclerostagonospora phragmiticola 0.169 1.525 0.973
Ascomycota Dothideomycetes Pleosporales Lentitheciaceae Setoseptoria arundinacea 0.123 0.000 0.050
Ascomycota Sordariomycetes Hypocreales Cordycipitaceae Simplicillium obclavatum 0.010 0.008 0.009
Ascomycota Sordariomycetes Hypocreales Cordycipitaceae Simplicillium sp. 0.001 0.000 0.001
Ascomycota Sordariomycetes Sordariomycetes 0.035 0.010 0.020
Basidiomycota Microbotryomycetes Sporidiobolales Sporidiobolaceae Sporobolomyces koalae 0.029 0.000 0.012
Ascomycota Dothideomycetes Pleosporales Massarinaceae Stagonospora neglecta 0.035 0.173 0.117
Ascomycota Dothideomycetes Pleosporales Pleosporaceae Stemphylium vesicarium 0.000 0.030 0.018
Ascomycota Dothideomycetes Chaetothyriales Incertae sedis Strelitziana africana 0.010 0.000 0.004
Ascomycota Dothideomycetes Chaetothyriales Incertae sedis Strelitziana eucalypti 0.013 0.000 0.005
Basidiomycota Cystobasidiomycetes Symmetrosporaceae Symmetrospora sp. 0.067 0.029 0.044
Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Teratosphaeria sp. 0.013 0.136 0.086
Ascomycota Dothideomycetes Capnodiales Teratosphaeriaceae Teratosphaeriaceae 0.798 4.551 3.024
Basidiomycota Agaricomycetes Polyporales Coriolaceae Trametes cubensis 0.004 0.006 0.005
Basidiomycota Tremellomycetes Tremellales Tremellales 0.032 0.000 0.013
Ascomycota Sordariomycetes Hypocreales Hypocreaceae Trichoderma lixii 0.000 0.011 0.007
Ascomycota Sordariomycetes Hypocreales Hypocreaceae Trichoderma sp. 0.035 0.044 0.040
Ascomycota Dothideomycetes Chaetothyriales Trichomeriaceae Trichomeriaceae 0.049 0.000 0.020
Ascomycota Dothideomycetes Capnodiales Dissoconiaceae Uwebraunia musae 0.003 0.000 0.001
Ascomycota Dothideomycetes Chaetothyriales Herpotrichiellaceae Veronaea botryosa 0.004 0.000 0.002
Ascomycota Dothideomycetes Pleosporales Sporomiaceae Westerdykella dispersa 0.332 0.277 0.299
Ascomycota Saccharomycetes Saccharomycetales Phaffomycetaceae Wickerhamomyces anomalus 0.000 0.006 0.003
Ascomycota Sordariomycetes Xylariales Xylariales 0.011 0.000 0.004
Ascomycota Dothideomycetes Capnodiales Mycosphaerellaceae Zasmidium sp. 0.108 0.000 0.044
DOI: 10.7717/peerj.7293/table-3

At genus and species levels, taxa having the highest percentage of occurrence included Alternaria sp. (3.46%), Cladosporium delicatulum (2.56%) and Pyrenochaetopsis leptospora (1.41%) in the winter samples, and Aureobasidium sp. (10.72%), Cladosporium sp. (7.90%), C. delicatulum (3.45%) and Hortaea werneckii (3.21%) in the summer samples (Table 3). These latter four species also had the highest overall percentage of occurrence (both seasons).

Calculated from the read numbers of the different OTUs, the fungal community in the winter samples had a higher species richness of 7.50 (Margalef) than that in the summer samples (5.29) but the Shannon–Wiener Diversity Index was comparable between the two samples, 1.98 and 2.09 respectively (Table 2). The overall Margalef and Shannon–Wiener Diversity indices were 8.11 and 2.28, respectively. The fungal community in both winter and summer samples had reached species saturation and the winter samples had a higher species diversity (Fig. 3B).

The fungal community among isolation/metabarcoding and winter/summer samples were analyzed by PCA and the result is shown in Fig. 5. A large extent of community variation was found across PC1 (87.03%), and to a lesser extent across PC2 (10.88%). Separation across PC1 was associated with changes in fungal composition between the methods; the fungal communities obtained from the metabarcoding method (Winter-NGS, Summer-NGS) were positively correlated while those obtained from the isolation method (Winter-Isolation, Summer-Isolation) were negatively correlated. For PC2, the community variation was associated with the summer and winter samples; the winter samples (Winter-NGS, Winter-Isolation) and the summer samples (Summer-NGS, Summer Isolation) were positively and negatively correlated, respectively.

Principle component analysis based on percentage of occurrence of foliar endophytic fungal communities of Acanthusilicifolius var. xiamenensis in summer and winter seasons obtained from isolation and metabarcoding (NGS) studies.

Figure 5: Principle component analysis based on percentage of occurrence of foliar endophytic fungal communities of Acanthusilicifolius var. xiamenensis in summer and winter seasons obtained from isolation and metabarcoding (NGS) studies.

Total diversity of fungi on Acanthus ilicifolius var. xiamenensis

Based on the average of the percentage of occurrence in the isolation study (Table 1) and metabarcoding analysis (Table 3), the phylum, class and order classifications of the fungi associated with A. ilicifolius var. xiamenensis were obtained (Figs. 4G4I). Ascomycota was still dominant, especially in the winter samples (Fig. 4G). The dominant classes in the winter and summer samples were Dothideomycetes and Sordariomycetes (Fig. 4H). Capnodiales, Diaporthales, Glomerellales and Pleosporales were dominant orders in both seasons, although varying in percentage of occurrences (Fig. 4I). The percentages of Dothideales and Hypocreales were much higher in the summer than in the winter.

Table 4 lists the species of fungi identified from the isolation and metabarcoding methods, excluding those taxa at the family level or above. Excluding the composite taxa (i.e., spp.), H. werneckii and Setoseptoria arundinacea were the only fungi recovered from both methods and at least 110 species were identified from leaves of A. ilicifolius var. xiamenensis. The most speciose genus on A. ilicifolius var. xiamenensis was Colletotrichum. Some genera were only obtained with the fungal isolation procedure such as Diaporthe spp., Phoma spp. and Pseudocercospora spp. while some were only recovered with the metabarcoding study, such as Aspergillus spp., Exophiala spp., Trichoderma spp. etc. Species of Alternaria, Aureobasidium, Cladosporium, Colletotrichum, Fusarium, Nigrospora, Pestalotiopsis and Phomopsis were identified with both methods.

Table 4:
Fungal taxa associated with leaves of Acanthus ilicifolius var. xiamenensis.
The list was summarized from results of the isolation and metabarcoding analyses.
ASCOMYCOTA BASIDIOMYCOTA
Botryosphaeriales Hypocreales Agaricales
Aplosporella yalgorensis Acremonium polychromum Psilocybe coprophila
Botryosphaeria dothideaa Fusarium oxysporuma Psilocybe sp.
Guignardia sp.a Fusarium solani Erythrobasidiales
Phyllosticta capitalensis Fusarium spp.b Erythrobasidium hasegawianum
Capnodiales Gibberella intricans Exobasidiales
Acidiella uranophilaa Simplicillium obclavatum Meira argovae
Cladosporium delicatulum Simplicillium sp. Geminibasidiales
Cladosporium spp.b Trichoderma lixii Geminibasidium sp.
Cladosporium sphaerospermum Trichoderma sp. Golubeviales
Devriesia sp. Pleosporales Golubevia pallescens
Mycosphaerella etlingerae Alternaria alternataa Hymenochaetales
Mycosphaerella sp. Alternaria spp.b Phellinus noxiusa
Phaeophleospora eucalypticolaa Coniothyrium sidae Malasseziales
Phaeophleospora hymenocallidicola Corynespora cassiicolaa Malassezia restricta
Pseudocercospora nymphaeaceaa Didymella spp.b Polyporales
Pseudocercospora sp.a Drechslera dematioideaa Bjerkandera adusta
Ramichloridium luteum Keissleriella yonaguniensis Phanerina melleaa
Ramichloridium punctatuma Leptospora rubella Phanerochaete tuberculata
Teratosphaeria capensisa Medicopsis romeroi Rigidoporus sp.
Teratosphaeria sp. Paraconiothyrium sp. Tinctoporellus epimiltinusa
Uwebraunia musae Parastagonospora phoenicicolaa Russulales
Zasmidium citria Phoma spp.a Peniophora sp.
Zasmidium sp. Preussia persica Sporidiobolales
Chaetothyriales Pyrenochaetopsis leptospora Rhodotorula mucilaginosa
Capronia semi-immersa Pyrenochaetopsis sp. Sporobolomyces koalae
Cyphellophora sessilis Roussoella solani Tremellales
Exophiala sp. Sclerostagonospora ericae Bullera unica
Exophiala xenobiotica Sclerostagonospora phragmiticola Cryptococcus dimennae
Strelitziana africana Septoriella hubertusiia Derxomyces sp.
Strelitziana eucalypti Setoseptoria arundinaceab Dioszegia sp.
Veronaea botryosa Stagonospora neglecta Dioszegia takashimae
Diaporthales Stagonosporopsis cucurbitacearuma Hannaella oryzae
Diaporthe endophyticaa Stemphylium vesicarium Kockovaella sacchari
Diaporthe longicollaa Westerdykella dispersa Papiliotrema pseudoalba
Diaporthe phaseoloruma Saccharomycetales Papiliotrema sp.
Phomopsis asparagi Wickerhamomyces anomalus Saitozyma flava
Phomopsis spp.b Venturiales Trametes cubensis
Dothideales Ochroconis musae Basidiomycota orderincertae sedis
Aureobasidium spp.b Xylariales Symmetrospora sp.
Aureobasidium thailandense Arthrinium sp.
Hortaea werneckiib Daldinia eschscholtziia
Eurotiales Hypoxylon monticulosum
Aspergillus penicillioides Nigrospora oryzae
Aspergillus sp. Nigrospora sp.a
Penicillium sp. Nodulisporium sp.a
Glomerellales Pestalotiopsis microsporaa
Colletotrichum boninensea Pestalotiopsis rhododendri
Colletotrichum brasiliense Phialemoniopsis ocularis
Colletotrichum gloeosporioides Xylaria sp.a
Colletotrichum hippeastria
Colletotrichum spp.a
DOI: 10.7717/peerj.7293/table-4

Notes:

From isolation.
from both methods.

Discussion

This study investigated the diversity of fungi associated with leaves of the mangrove plant Acanthus ilicifolius var. xiamenensis using the traditional isolation technique and the metabarcoding approach. In the isolation study, most of the isolates did not fruit on the agar plates and sequence analysis of the internal transcribed spacer regions of the rDNA including the 5.8S rDNA (ITS) was used to identify the cultures. ITS is easily amplifiable by PCR and has the highest probability of successful identification for the broadest range of fungi as compared to other rDNA regions and protein genes (Schoch et al., 2012). In the metabarcoding analysis, many OTUs were only identified to the phylum or kingdom levels (Table 3) and the UNITE database was not extensive enough to identify these sequences down to genus/species level (Nilsson et al., 2019). However, the metabarcoding approach offers the advantages of finding signatures of unculturable fungi and potential cryptic species not identifiable with other methods. The nested PCR approach used in this study was found to be able to specifically amplify fungal sequences in the samples.

The leaves were surface-sterilized before isolation and therefore the diversity of fungi recovered from isolation represented the endophytic fungal diversity. On the other hand, the diversity obtained from the metabarcoding analysis represented predominantly endophytic fungi and might represent partial diversity of the epiphytic fungi as surface sterilization of leaves by sodium hypochlorite and ethanol does not completely eliminate all fungal DNA on the surface of the leaves (Burgdorf et al., 2014). This might have resulted in the differences in fungal richness (Margalef species richness, total richness) between the two methods, i.e., generally higher in the metabarcoding analysis (winter: 7.50 (Margalef), 96 species, summer: 5.29, 70) than in the isolation study (winter: 6.24, 30, summer: 5.44, 26) although the Shannon–Wiener diversity index of the two samples was comparable.

The winter samples had a higher fungal species diversity. The weather conditions of Kinmen, Taiwan in January 2014, when the winter samples were collected, were much colder and drier (13.7 °C, 0 mm rainfall, 65% relative humidity) than July 2014 (29.8 °C, 106.9 mm rainfall, 81% relative humidity) for the summer samples. Generally, higher richness and abundance of endophytic fungi were found in hotter and wetter seasons (Pang et al., 2008).

Only nine out of a total of 47 fungal species isolated from A. ilicifolius var. xiamenensis were common between the two sampling times, showing a seasonal variation of fungal diversity using the culture method. However from the metabarcoding analysis, 55 taxa were found to be common between the winter and summer samples (41 and 15 exclusive fungi in the winter and summer samples, respectively), suggesting there was an overall similarity in fungal diversity between the samples. These results show the weakness of using isolation techniques as the sole methods to study diversity of endophytic fungi of mangrove plants (Abdelfattah et al., 2015) Inoculation of leaf discs on a nutritious medium always favors fast-growing fungi to be isolated. In addition, the isolation medium (MEAF) used in this study only recovered a fraction of culturable fungal diversity and it is advisable to use multiple media to widen the number of fungal isolates (Rosa et al., 2011; Potshangbam et al., 2017). Three basidiomycetes Phellinus noxius, Phanerina mellea and Tinctoporellus epimiltinus were isolated from the summer samples, but a number of basidiomycetous OTUs were recovered from both seasons from the metabarcoding analysis and this further confirms the importance of culture-independent techniques in studying diversity of fungi.

A core group of culturable endophytic fungi was found to be associated with mangrove plants, including species of the genera Acremonium, Cladosporium, Colletotrichum, Fusarium, Pestalotiopsis, Phyllosticta (sexual morph Guignardia), Phoma, Phomopsis (sexual morph Diaporthe) and Sporomiella (Pang et al., 2008). Many of these genera, such as Acremonium, Cladosporium, Phomopsis, Phyllosticta, among others, were isolated from leaves of A. ilicifolius var. xiamenensis in this study, confirming their prevalence in mangrove plants. However, Sporomiella, a universal endophytic taxon of mangrove plants, was not found in this study (Pang et al., 2008). The number of species isolated from leaves of A. ilicifolius var. xiamenensis (47) was much higher than those found in related studies in this species: 11 species from roots in Udupi, India (Ananda & Sridhar, 2002), 10 species from leaves in Ranong, Thailand (Chaeprasert et al., 2010), eight species from leaves in Tamil Nadu, India (Suryanarayanan & Kumaresan, 2000) and 14 species from leaves in Muthupet, India (Priyadharshini, Ambikapathy & Panneerselvam, 2015). However, the fungal community obtained from the metabarcoding analysis was different from that of the isolation study. The dominant fungi included Cladosporium spp. and other common terrestrial fungi, such as Hortaea werneckii. H. werneckii is a cosmopolitan halophilic fungus and can potentially cause human diseases (Marchetta et al., 2018). Together with Setoseptoria arundinacea, H. werneckii was also cultured from leaves of A. ilicifolius var. xiamenensis and it was previously reported from surface-sterilized roots and stems of the mangrove plant Aegiceras corniculatum (Chen et al., 2012).

At least 110 species (excluding the composite genera) were obtained from both isolation and metabarcoding studies suggesting a much higher fungal diversity associated with leaves of A. ilicifolius var. xiamenensis. Ascomycota was dominant with a small proportion of Basidiomycota from both methods, agreeing with similar studies using the traditional culture methods (Hamzah et al., 2018; Zhou et al., 2018) and with Arfi et al. (2012) who used a culture-independent approach. As expected, Basidiomycetes were not commonly cultured as endophytes (Chaeprasert et al., 2010; Xing & Guo, 2011; Costa, Maia & Cavalcanti, 2012).

Dothideomycetes was found to be the most dominant class in both seasons from both methods. Dothideomycetes were also found to be the dominant class of fungi on the aerial parts (trunk, bark and leaf) of the mangrove plants Avicennia marina and Rhizophora stylosa and Lecanoromycetes in R. stylosa using 454 pyrosequencing of 18S and ITS rDNA genes (Arfi et al., 2012). Lecanoromycetes is a group of lichenized fungi; it was not found in this study, probably because tree trunk and bark, where this group of fungi normally inhabits, were not analyzed. Also according to Arfi et al. (2012), Capnodiales, Diaporthales, Dothideales and Pleosporales were dominant on the emerged plant parts, especially in A. marina. This result generally agrees with this study, with variations related to the abundance.

A number of fungi recovered from A. ilicifolius var. xiamenensis are well known pathogens such as Cladosporium, Colletotrichum, and Fusarium, which might ultimately cause plant diseases. The Botryosphaeriales was reported to potentially cause diseases of mangrove plants (Osorio et al., 2017). In this study, Aplosporella yalgorensis, Botryosphaeria dothidea, Guignardia sp. and Phyllosticta capitalensis of the Botryosphaeriales were recovered. Whether these fungi cause diseases in A. ilicifolius var. xiamenensis is not known and requires further research. A Purpureocillium sp. isolated endophytically from roots of Kandelia candel was found to protect growth of the plant from copper(II) stress when this fungus was added to the growth pots (Gong et al., 2017). Whether endophytic fungi help to relief metal stress imposed on mangrove plants also requires further studies. A high quantity of RNA transcripts of fungi from surface-sterilized leaves of A. marina was found (Huang et al., 2014) and it may suggest that endophytic fungi live in a close symbiotic relationship with the mangrove plant.

In conclusion, this study discovered a high diversity of fungi associated with leaves of A. ilicifolius var. xiamenensis with a total of 110 taxa recovered from the isolation and metabarcoding methods. From the isolation study, Ascomycota was dominant, with Basidiomycota isolated only in the summer samples. C. cassiicola (6.90%), F. oxysporum (6.40%) and Guignardia sp. (6.40%) had the highest overall percentage of occurrence. In the metabarcoding analysis, Ascomycota was also dominant over the Basidiomycota. Based on reads, Aureobasidium sp. (10.72%), Cladosporium sp. (7.90%), C. delicatulum (3.45%) and H. werneckii (3.21%) had the highest percentage of occurrence. The use of both methods discovered a much higher diversity of endophytic fungi associated with A. ilicifolius var. xiamenensis. The association of these fungi with the plant is not known and future studies should focus on the ecological roles of these fungi. However, a chemical analysis of the spent culture liquid of the fungal isolates in this study suggests that 28 isolates produced antimicrobial substances against some Gram-positive and Gram-negative bacteria and fungi and thus might protect the plant from microbial diseases (Chi et al., 2019).

Supplemental Information

Raw sequence data for internal transcribed spacer regions of the rDNA including 5.8S (ITS) of fungi isolated from Acanthus ilicifolius var. xiamenensis

The fungal isolates were cultured from leaves of Acanthus ilicifolius var. xiamenensis collected at Lieyu Township, Kinmen County, Taiwan on malt extract freshwater agar supplemented with antibiotics.

DOI: 10.7717/peerj.7293/supp-1
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