Research Article |
Corresponding author: Zefen Yu ( zfyu2021@163.com ) Academic editor: Rungtiwa Phookamsak
© 2021 Xiao Qian Yang, Shi Yun Ma, Ze Xiang Peng, Zhong Qiao Wang, Min Qiao, Zefen Yu.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yang XQ, Ma SY, Peng ZX, Wang ZQ, Qiao M, Yu Z (2021) Diversity of Plectosphaerella within aquatic plants from southwest China, with P. endophytica and P. sichuanensis spp. nov. MycoKeys 80: 57-75. https://doi.org/10.3897/mycokeys.80.64624
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Members of Plectosphaerella inhabit different substrates, including plants, soil and insects, and most species are pathogens causing large losses in agriculture. During a survey of endophytic fungi in aquatic plants in southwest China, 112 strains of Plectosphaerella were isolated, representing two new species, P. endophytica sp. nov. and P. sichuanensis sp. nov., as well as two known species, P. cucumerina and P. pauciseptata. The novel taxa are described and illustrated here using combined morphological and multi-locus phylogenetic (LSU-ITS-TEF-1α-TUB2) analyses. Our result revealed Plectosphaerella species inhabiting within aquatic plants in southwest China, and the separation frequency of each species was presented.
Endophytic fungi, multi-locus phylogeny, new species, Plectosphaerellaceae, Sordariomycetes
The genus Plectosphaerella Kleb. was established to accommodate P. cucumeris Kleb. from young cucumber plants (
Species of Plectosphaerella are distributed in a variety of habitats and have wide geographic distribution (
Plectosphaerella cucumerina is the most widely distributed species, thriving on more than nine plant genera: Arabidopsis, Cucumis, Galium, Hydrilla, Nicotiana, Pyrus, Solanum, Viola and Austropotamobius etc., and also occurring in soil and paper (
During our investigation of endophytic fungal diversity of aquatic plants in southwest China, among 1697 acquired strains, 112 strains belonging to Plectosphaerella were isolated. Based on morphological characteristics and phylogenetic analysis, two known species, P. cucumerina and P. pauciseptata, were described, and two new species, P. endophytica and P. sichuanensis, were proposed and illustrated. The geographic distribution and habitat diversity of Plectosphaerella in this study were also discussed.
Samples were collected from Yunnan, Guizhou, Sichuan provinces, Chongqing and Tibet from 2014 to 2017. The dominant hosts are Myriophyllum, Potamogeton, Hydrilla and Hippuris. Samples were placed in plastic bags, labeled and transported to the laboratory. Each leaf and stem was cut into segments 30–40 mm in length and washed thoroughly with tap water, then a surface-disinfection was carried out according to
Pure cultures were deposited in the Herbarium of the Laboratory for Conservation and Utilization of Bio resources, Yunnan University, Kunming, Yunnan, P.R. China (
Actively growing mycelium was scraped off from the surface of the culture and transferred to 2 ml Eppendorf micro-centrifuge tubes. Total genomic DNA was extracted follow the protocol of
The ITS sequences generated in this study were used as a query to search similar DNA sequences using BLASTn. All published DNA sequences were obtained from the GenBank from relevant studies (
Maximum-likelihood (ML) analysis was conducted by using RAxML (
A total of 112 strains were identified as members of Plectosphaerella according to the BLASTn search results using the ITS sequences. At first, we carried out individual phylogenetic analyses with ITS sequences to resolve the taxonomic position of our strains using the sequences of the accepted species into Plectosphaerella. This tree is shown in Figure
Phylogenetic tree inferred from a Bayesian analysis based on ITS sequences of 112 Plectosphaerella strains obtained in this study. BIPP over 80% are shown on the respective branches. The scale bar shows the expected changes per site. Two new species are given in boldface. Monilochaetes infuscans CBS 379.77 serves as an outgroup.
The four Bayesian trees derived from the single-gene sequence alignments (LSU, ITS, TEF-1α, TUB2) confirmed that the novel taxa were distant from other known species in Plectosphaerella. The Bayesian trees are available in the Suppl. material
Phylogenetic tree of Plectosphaerella based on Bayesian analyses and Maximum Likelihood analyses of the combined sequences dataset of LSU, ITS, TEF-1α and TUB2. The numbers above branches represent BIPP (left) and MLBPs (right). BIPP over 80% and MLBPs over 50% are shown on the respective branches. The scale bar shows the expected changes per site. Two new species are given in boldface. Monilochaetes infuscans CBS 379.77 serves as an outgroup.
Latin, endophytica meaning endophytic, growing within plant tissue.
Colony on CMA after 3 d, hyphae hyaline, smooth, septate, thin-walled, branched, 1.9–3.3 µm (x̄ = 2.6 μm, n = 10) wide. Conidiophores macronematous, mononematous, erect, straight or flexuous, smooth-walled, hyaline, unbranched or occasionally irregular branched, sometimes 1–2-septate. Conidiogenous cells phialides, subulate, integrated, terminal, determinate, hyaline, smooth-walled. Conidia solitary, acrogenous, broadly navicular to broadly fusiform, suboblong or ellipsoidal, 0–1-septate, usually constricted at septum, bi-guttulate, hyaline, smooth-walled, aseptate conidia abundant, 5–9.1 × 2.5–3.5 µm (x̄ = 7.8 × 3.1 µm, n = 30); septate conidia scarce, 8.8–10.1 × 3.7–4.6 µm (x̄ = 9.4 × 4.1 µm, n = 30), forming hyaline to white mucilaginous masses. Sexual morph and chlamydospores absent.
Colonies on OA reaching 52 mm diameter, on PDA reaching 48 mm diameter and on CMA reaching 43 mm diameter in 14 d at 25 °C. On PDA, colonies white, dense, fluffy hyphae growth in the medium surface, outermost mycelia formed an annule, margin smooth and entire, sporulation abundant, reverse pale yellow to white.
China, Yunnan Province, Kunming, The Dian Lake, 24°96'N, 102°66'E, 1886 m alt., isolated from Hydrilla verticillata (L.f.) Royle as an endophyte, 20 Jul. 2014, Z.F. Yu,
Although the phylogenetic analyses showed that our isolate Plectosphaerella endophytica is close to P. oratosquillae, the conidia of P. oratosquillae are aseptate, multi-guttulate (
Latin, sichuanensis, referred to Sichuan Province, the locality where the fungus was found.
Colony on CMA after 3 d, vegetative hyphae hyaline, septate, commonly branched, smooth, thin-walled, mostly 2.5–3.5 μm (x̄ = 2.9 μm, n = 10) wide. Conidiophores macronematous, mononematous, erect, straight or flexuous to sinuate, hyaline, smooth, unbranched or rarely branched, aseptate. Conidiogenous cells phialides, integrated, terminal, determinate, subulate, hyaline, smooth. Conidia acrogenous, ellipsoidal, unicellular, smooth-walled, hyaline, 1–3 guttulate, 4.2–6.8 × 2.5–3.7 μm (x̄ = 5.2 × 3.3 µm, n = 30), forming hyaline to white mucilaginous masses. Sexual morph and chlamydospores absent.
Colonies on OA reaching 50 mm diameter, on PDA reaching 47 mm diameter and on CMA reaching 42 mm diameter in 14 d at 25 °C. On PDA, colonies pale brown to white, flat, repressed, plicated, partly immersed, a few white aerial hyphae grew in the middle of the medium, margin regular, frontier distinct, reverse pale brown to white.
China, Sichuan Province, Daofu, 30°98'N, 101°13'E, 2960 m alt., isolated from Potamogeton pectinatus as an endophyte, 20 Jul. 2015, Z.F. Yu,
In the phylogenetic tree, the closest species to Plectosphaerella sichuanensis is P. populi, but P. populi can be distinguished from P. sichuanensis by its smaller aseptate conidia (
Colony on CMA after 3 d, hyphae hyaline, septate, smooth, thin-walled, branched, 2.5–3.5 μm (x̄ = 3.2 μm, n = 10) wide. Conidiophores macronematous, mononematous, erect or flexuous to sinuate, hyaline, smooth, branched, occasionally forming hyphal coils. Conidiogenous cells phialides, terminal, determinate, subulate. Conidia acrogenous, hyaline, unicellular, smooth-walled, oblong-ellipsoidal, 1–2 guttulate, 6.6–10.7 × 2.3–3.6 μm (x̄ = 8.7 × 3.1 µm, n = 30), forming hyaline to white mucilaginous masses. Sexual morph and chlamydospores absent.
Colonies on OA reaching 55 mm diameter, on PDA reaching 48 mm diameter and on CMA reaching 44 mm diameter in 14 d at 25 °C. On PDA, colonies pale brown, repressed, flat, partly immersed, some aerial hyphae grew in the middle and margin of the medium, margin regular, reverse pale brown.
China, Sichuan Province, Baiyu, 31°00'N, 99°41'E, 4013 m alt., isolated from Myriophyllum spicatum as an endophyte, 20 Aug. 2015, Z.F. Yu,
Colony on CMA after 3 d, hyphae hyaline, septate, commonly branched, thin-walled, smooth, 2.5–3.0 μm (x̄ = 2.6 μm, n = 10) wide. Conidiophores macronematous, mononematous, erect, straight or flexuous, hyaline, smooth, aseptate, occasionally branched. Conidiogenous cells phialides, terminal, determinate, subulate, hyaline, smooth, thin-walled. Conidia acrogenous, hyaline, oblong-ellipsoidal, unicellular, smooth-walled, multi-guttulate, 5.5–12.5 × 2.5–3.5 μm (x̄ = 9.7 × 3.3 µm, n = 30), forming hyaline to white mucilaginous masses. Sexual morph and chlamydospores absent.
Colonies on OA reaching 55 mm diameter, on PDA reaching 49 mm diameter and on CMA reaching 45 mm diameter in 14 d at 25 °C. On PDA, colonies white, dense, raised, aerial hyphae growth in the medium surface, margin regular, frontier distinct, reverse pale brown to white.
China, Yunnan Province, Erhai, 25°43'N, 100°11'E, 1964 m alt., isolated from Myriophyllum spicatum as an endophyte, 31 Jul. 2014, Z.F. Yu,
Sexual reproduction of Plectosphaerella has only been reported for three species (
In this study, among 129 sample sites in Yunnan and Sichuan province, Plectosphaerella species were isolated from 13 sampling sites. Regions are arranged in order of isolation frequency: Eehai (39.29%), Dian Lake (20.54%), Fuxian Lake (13.39%), Daofu (8.04%) and other places were below 5%. It seems that distribution of Plectosphaerella is impacted by human activities, because there are more human activities around the first three sites. In addition, Plectosphaerella species only occur in six aquatic plants including Batrachium, Halerpestes, Hippuris, Hydrilla, Myriophyllum, and Potamogeton, although we investigated 30 aquatic plants. So Plectosphaerella species exhibit medium host diversity and relatively narrow geographic distribution when aquatic plants serve as hosts.
Secondly, the separation frequency of Plectosphaerella pauciseptata was the highest at 68.78%, followed by P. cucumerina at 24.11%, and two new species were the lowest at 3.57%. According to this data and previous studies, P. cucumerina and P. pauciseptata are still the most widely distributed species either on land or within aquatic plants, although P. pauciseptata is more common in aquatic plants. On the other hand, only four species were identified among 112 strains. One reason may be that species diversity of Plectosphaerella is low within aquatic plants. Other reasons may be Plectosphaerella species exhibit a relatively low degree of ITS molecular diversity. Based on this, perhaps we treat some different species as two known species, which reduce the diversity of Plectosphaerella. Regrettably, we did not preserve all strains except for representative strains. Or else, we should sequence other loci of all strains, especially for two species, P. pauciseptata, P. cucumerina, more loci are needed to distinguish them.
This study revealed Plectosphaerella species within aquatic plants from the southwest of China, although only 112 strains and four species were reported, which also enrich the ecology and diversity of the genus. However, our survey was limited, hence it is necessary to know if our result is concordant with those of other regions. So in-depth work is required to obtain a more integrated knowledge of their biodiversity and distribution in water bodies.
This work was financed by the National Natural Science Foundation Program of P.R. China (31770026, 31760012). We are grateful to two reviewers for critically reviewing the manuscript and for providing helpful suggestions to improve this paper.
Figures S1–S4
Data type: phylogenetic tree
Explanation note: Figure S1. Phylogenetic tree generated by Bayesian inference based on sequences of the ITS. Monilochaetes infuscans CBS 379.77 serves as an outgroup. Bayesian posterior probability over 80% are shown at the nodes. Two new species are given in boldface. Figure S2. Phylogenetic tree generated by Bayesian inference based on sequences of the LSU. Monilochaetes infuscans CBS 379.77 serves as an outgroup. Bayesian posterior probability over 80% are shown at the nodes. Two new species are given in boldface. Figure S3. Phylogenetic tree generated by Bayesian inference based on sequences of the TEF-1α. Bayesian posterior probability over 80% are shown at the nodes. Two new species are given in boldface. Figure S4. Phylogenetic tree generated by Bayesian inference based on sequences of the TUB2. Bayesian posterior probability over 80% are shown at the nodes. Two new species are given in boldface.