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Research Article
Morphological and molecular identification of two new Alternaria species (Ascomycota, Pleosporaceae) in section Radicina from China
expand article infoLin He, Hong Cheng, Lin Zhao, Aye Aye Htun, Zhi He Yu, Jian Xin Deng, Qi Li Li§
‡ Yangtze University, Jingzhou, China
§ Institute of Plant Protection, Guangxi Academy of Agricultural Sciences and Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests, Nanning, China
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Abstract

The fungal genus Alternaria was distributed widely and found in different habitats such as plant or indoor environment. During an investigation into this genus in China, two new Alternaria species, Alternaria vulgarae and A. divaricatae were respectively isolated from diseased leaves of Foeniculum vulgare and Saposhnikovia divaricata, which both belonged to Umbelliferae. Phylogenetically, they were determined as new species belonging in the section Radicina of Alternaria based on the combined four gene fragments of ITS, TEF1, GAPDH and RPB2. Morphologically, the two species were illustrated and compared with other relevant Alternaria species in section Radicina.

Keywords

Alternaria, new taxon, phylogeny, Pleosporaceae, taxonomy

Introduction

Alternaria Nees (1816) was typified by Alternaria tenuis (the synonym of A. alternata), a species with muriform and catenulate conidia. Since then, hundreds of new species were proposed in the genus. Meanwhile, because of unstable taxonomic standards (morphological characteristics, host and growing environment, etc.), the controversies about species boundary started and never stopped (Elliott 1917; Fries 1832; Neergaard 1945; Joly 1964; Wiltshire 1933; Simmons 1967, 1992). In 1992, Simmons introduced reasonable standards to get unified taxonomic concepts on Alternaria species based on colony and conidial morphology. At the same time, the concept of species-group was introduced, the small-spored, catenulate taxa of Alternaria were divided into six morphological groups by Simmons and Roberts (1993). More recently, around 300 Alternaria morphospecies have been accepted based on the shape, size, septation of conidia, as well as sporulation patterns. Small-spored Alternaria species were also redefined and divided into 10 subsections characterized by short (>50(–60) μm) or medium (50–100(–105) μm) conidia produced in various patterns of branched and unbranched chains or solitary (Simmons 2007). However, the identification remained challenging due to the impact of environmental conditions and other unknown factors.

On the other hand, multigene phylogenetic analyses have provided strong support for the re-definition of the Alternaria genus. Many sequences of gene regions such as the internal transcribed spacer region of rDNA (ITS), large subunit ribosomal DNA (LSU), mitochondrial small subunit (mtSSU), Alternaria major allergen (ALT), glyceraldehydes-3-phosphate dehydrogenase (GAPDH), translation elongation factor 1-alpha (TEF1), RNA polymerase second largest subunit (RPB2), and ATPase etc. were applied to delimit the genus (Pryor and Gilbertson 2000; Hong et al. 2005; Lawrence et al. 2012, 2013; Woudenberg et al. 2013, 2014; Poursafar et al. 2018). In recent studies, both morphological and molecular analyses were used for the delimitation of the genus Alternaria, which has been divided into 28 sections and eight monotypic lineages (Woudenberg et al. 2013; Lawrence et al. 2016; Ghafri et al. 2019; Marin-Felix et al. 2019). The number of Alternaria species has been continuously growing after re-descriptions and new discovery (Deng et al. 2018; Ahmadpour 2019: Liu et al. 2019; Tao et al. 2019; Bessadat et al. 2020; He et al. 2020). Coincidentally, several phylogenetic lineages have strongly supported morphology-based sections but others not (Simmons 2007; Woudenberg et al. 2015).

During the investigation into Alternaria species in China, two new taxa were isolated from umbelliferous plants, Foeniculum vulgare and Saposhnikovia divaricata. The study was designed to determine them based on a polyphasic approach including morphology and phylogenetic analyses.

Materials and methods

Isolation and morphological studies

Leaves of Foeniculum vulgare and Saposhnikovia divaricata with necrotic spots were respectively collected from Wenjiang district (Chengdu, Sichuan in June, 2015) and Badong county (Yichang, Hubei in July, 2016) in China. For fungal isolation, the samples were stored in sterile plastic bags and transported to the laboratory. The tissues were cut into small segments and placed on moist filter papers within Petri dishes then incubated at 25 °C to stimulate sporulation. After 24 h, the samples were examined under a stereomicroscope. Alternaria-like spores were picked up and inoculated to potato dextrose agar (PDA: Difco, Montreal, Canada) using sterilized glass needles. All isolated pure cultures were inoculated to test-tube slants and stored at 4 °C. Dried cultures from the single spore and ex-type strains were deposited in the Fungi Herbarium of Yangtze University (YZU), Jingzhou, Hubei, China.

To determine colonial characteristics (size, color and texture of colony), the strains were cultured on PDA at 25 °C for 7 days in darkness. To analyze the morphological features of conidia (conidial size, shape, sporulation, etc.), fresh mycelia were transferred on potato carrot agar (PCA) and V8 juice agar (V8A) then incubated at 22 °C under an 8 hour photoperiod for 7 days (Simmons 2007). Conidia were mounted into a lactophenol picric acid solution and digital images were captured under a Nikon ECLIPSE Ni-U microscope system (Nikon, Japan). Conidia (n = 50) were randomly selected for determining the morphology and sporulation patterns were also photographed at the same time.

DNA extraction, PCR amplification and sequencing

Genomic DNA was extracted from fresh mycelia growing on PDA after 3–5 days of growth following the CTAB method described in Watanabe et al. (2010). For amplification of the ITS, TEF1, GAPDH and RPB2 gene fragments, the primer pairs ITS5/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), gpd1/gpd2 (Berbee et al. 1999) and RPB2-5F/RPB2-7cR (Liu et al. 1999) were used, respectively. A total of 25 μL of a PCR reaction mixture containing 21μL of 1.1×Taq PCR Star Mix (TSINGKE, Beijing, China), 2 μL template DNA and 1μL of each primer was prepared and the PCR was performed in an Eppendorf Mastercycler following the protocols described by Woudenberg et al. (2013). Successful products were purified and sequenced by TSINGKE company (Beijing, China). All sequences were assembled with BioEdit (Hall 1999) and deposited at GenBank (https://www.ncbi.nlm.nih.gov/) (Table 1).

Table 1.

Alternaria strains and their accession numbers used in the phylogenetic analysis.

Section Species Strain Host/Substrate Country GenBank accession numbers
ITS GAPDH TEF1 RPB2
Alternaria A. alternata CBS 916.96 T Arachis hypogaea India AF347031 AY278808 KC584634 KC584375
A. tenuissima CBS 918.96 R Dianthus sp. UK AF347032 AY278809 KC584693 KC584435
Althernantherae A. alternantherae CBS 124392 Solanum melongena China KC584179 KC584096 KC584633 KC584374
A. perpunctulata CBS 115267 T Alternanthera philoxeroides USA KC584210 KC584129 KC584676 KC584418
Gypsophilae A. gypsophilae CBS 107.41 T Gypsophila elegans USA KC584199 KC584118 KC584660 KC584401
A. nobilis CBS 116490 R Dianthus caryophyllus New Zealand KC584208 KC584127 KC584673 KC584415
A. vaccariae CBS 116533 R Vaccaria hispanica USA KC584223 KC584146 KC584696 KC584438
A. vaccariicola CBS 118714 T Vaccaria hispanica USA KC584224 KC584147 KC584697 KC584439
Radicina A. carotiincultae CBS 109381 T Daucus carota USA KC584188 KC584106 KC584645 KC584386
A. chlamydosporifera FMR 17360 T Rabbit dung Spain LR133924 LR133927 LR133929 LR133926
A. divaricatae sp. nov. YZU 151055 T Saposhnikovia divaricata China MW541932 MW579314 MW579316
YZU 151059 Saposhnikovia divaricata China MW541933 MW579315 MW579317
A. glehniae YZU 161149 T Glehnia littoralis China MK279385 MK279392 MK279394
A. petroselini CBS 112.41 T Petroselinum sativum Unknown KC584211 KC584130 KC584677 KC584419
A. radicina CBS 245.67 T Daucus carota USA KC584213 KC584133 KC584681 KC584423
A. selini CBS 109382 T Petroselinum crispum Saudi Arabia AF229455 AY278800 KC584684 KC584426
A. smyrnii CBS 109380 R Smyrnium olusatrum UK AF229456 KC584138 KC584687 KC584429
A. vulgarae sp. nov. YZU 161234 T Foeniculum vulgare China MW541936 MW579308 MW579310 MW579312
YZU 161235 Foeniculum vulgare China MW541937 MW579309 MW579311 MW579313
Porri A. dauci CBS 117097 R Daucus carota USA KC584192 KC584111 KC584651 KC584392
A. porri CBS 116698 R Allium cepa USA DQ323700 KC584132 KC584679 KC584421
Sonchi A. cinerariae CBS 116495 R Ligularia sp. USA KC584190 KC584109 KC584648 KC584389
A. sonchi CBS 119675 R Sonchus asper Canada KC584220 KC584142 KC584691 KC584433
Out-group Stemphylium herbarum CBS 191.86 T Medicago sativa India KC584239 AF443884 KC584731 KC584471

Phylogenetic analyses

Preliminary BLAST searches in GenBank with ITS and TEF1 sequences of the present isolates indicated that they had a close phylogenetic relationship with species from section Radicina of Alternaria. Subsequently, sequence data of 19 Alternaria species and Stemphylium herbarum CBS 191.86 (outgroup) were retrieved from National Center for Biotechnology Information (NCBI), mostly published in Marin-Felix et al. (2019), Woudenberg et al. (2013), and Tao et al. (2019) (Table 1). The gene sequences were concatenated and edited manually according to ITS+TEF1+GAPDH+RPB2 for YZU 161234 and YZU 161235 and ITS+TEF1+RPB2 for YZU 151055 and YZU 151059 with equal weight in MEGA v.7.0.26 (Kumar et al. 2016). Maximum parsimony (MP) analysis was performed in PAUP 4.0 (Swofford 2002) using the heuristic search option of 1000 random-addition sequences and tree bisection and reconnection (TBR) as the branch-swapping algorithm. Gaps were treated as missing data. The bootstrap values (BS) with 1000 replicates were performed to determine branch support. Parsimony scores of tree length (TL), consistency index (CI), retention index (RI) and rescaled consistency (RC) were calculated for each generated tree. The Bayesian inference (BI) analysis was performed with a Markov Chain Monte Carlo (MCMC) algorithm with Bayesian posterior probabilities in MrBayes v. 3.2.1 (Ronquist et al. 2012). The best-fit evolutionary models (GTR+I+G) were determined in MrModel-test v. 2.3 (Posada and Crandall 1998) using the Akaike Information Criterion (AIC). Two independent analyses with four chains each were run for 10,000,000 generations. Trees were sampled every 100th generation. The run was stopped until the standard deviation of split frequencies reaches < 0.01 and the initial 25 % of the trees were discarded as the burn-in phase of each analysis. Maximum likelihood (ML) analysis was performed using RAxML v.7.2.8 (Stamatakis 2006), implementing GTRCAT model and executing 1000 rapid ML bootstrap replications. Branch support equal to or above 0.70/70%/70% for PP (posterior probability of BI analysis) and BS (bootstrap for ML and MP analyses) values were shown at the nodes in the phylogram.

Results

Phylogenetic analyses

The combined dataset of twenty-four strains (including 20 references and present four strains) had a length of 2166 characters with gaps after alignment, 536 characters for ITS, 247 for TEF1, 537 for GAPDH and 846 for RPB2. Of these characters, 1555 were constant and 198 were variable and parsimony-uninformative. MP analysis of the remaining 413 parsimony-informative characters resulted in one parsimonious tree of 995 lengths (CI = 0.739, RI = 0.815, RC = 0.602); Tree topologies computed from the MP, BI, and ML analysis were similar and the ML tree was shown in Fig. 1. The results indicated that all strains in the present study fell into the section Radicina with PP/BS (BI/ML/MP) values of 1/100%/100%. The strains YZU 161234 and YZU 161235 were clustered with A. petroselini and A. selini in a clade supported by values of 1.0/91%/90% (BI/ML/MP). This clade was sister to a separate clade containing the other two strains (YZU 151055, YZU 151059) supported by PP value of 0.95 and BS values of 77%/70% (ML/MP) (Fig. 1).

Figure 1. 

Phylogenetic tree based on the combined gene sequences of ITS, TEF1, GAPDH, and RPB2. The Bayesian posterior probabilities >0.70 (PP), maximum likelihood and maximum parsimony bootstrap support values >70 (BS) are given at the nodes (PP/BS). Examined strains are in bold.

Taxonomy

Alternaria divaricatae L. He & J.X. Deng, sp. nov.

MycoBank No: 838893
Figure 2

Type

China, Sichuan Province, Chengdu City, Wenjiang District, Herb Garden of Chengdu University of Traditional Chinese Medicine, from leaf spot of Saposhnikovia divaricata. 17 June, 2015, J.X Deng, (YZU-H-0029, holotype), ex-type culture YZU 151055.

Etymology

In reference to the host species name, divaricata.

Description

Colonies on PDA (Fig. 2A) vinaceous buff, hazel in the center, velvety, cottony, dark mouse grey to pale mouse grey in reverse, 56‒64 mm in diam.; On PCA, conidiophores arising directly from lateral or apical of aerial hyphae or medium, lightly flexuous, sometimes geniculate at apex, smooth-walled, 9–36 × 3.5–6 μm, 1–3 transverse septa, the aerial hyphae sometimes up to 82–400 × 4–6 μm; conidia solitary from apex or geniculate loci, short-ovoid, subglobose, ellipsoid, 21–38 × 12–26 μm, with 1–4 transverse septa and 1‒4 longitudinal septa (Fig. 2B, D, E); On V8A, conidiophores 10–26 (–53) × 3–4 μm, 1‒7 transverse septa, conidia 22–39 × 13–24 μm, 1‒4 transverse septa, 1‒3 longitudinal or oblique between septa (Fig. 2C, F, G). There was no secondary conidium production observed on PCA and V8A medium.

Figure 2. 

Morphological characteristics of Alternaria divaricatae (strain: YZU 151055). Colony on PDA for 7 days at 25 °C (A); Conidia on PCA and V8A (B, C); Sporulation patterns from PCA and V8A (D–G: D, E from PCA F, G from V8A); Scale bars: 25 µm (B, C); 2 µm (D, F); 50 µm (E); 100 µm (G).

Additional isolate examined

China, Sichuan Province, Chengdu City, Wenjiang District, Herb Garden of Chengdu University of Traditional Chinese Medicine, from leaf spot of Saposhnikovia divaricata. 17 June, 2015, L He, living culture YZU 151059.

Notes

Phylogenetically, Alternaria divaricatae forms a distinct clade in section Radicina, which appears to be sister to a clade including A. petroselini, A. selini and A. vulgarae (Fig. 1). Morphologically, A. divaricatae was different from A. petroselini, A. selini and A. vulgarae by producing smaller conidia (Table 2) and special sporulation from apex or geniculate loci of lateral or apical of aerial hyphae. Moreover, A. chlamydosporifera, A. glehniae and A. smyrnii grouped together and clustered as a sister clade with A. divaricatae, A. petroselini, A. selini and A. vulgarae (Fig. 1). Obviously, the conidia of A. divaricatae was smaller than A. smyrnii (Table 2) and A. divaricatae could be also easily differentiated from A. chlamydosporifera by the lack of chlamydospores in culture (Marin-Felix et al. 2019). Meanwhile, A. glehniae was distinguished from A. divaricatae by its single conidium on apex of conidiophore (there was no geniculate sporulation loci) and production of secondary conidium (Tao et al. 2019). In addition, A. radicina and A. carotiincultae were distinguished from present species by distant phylogenetic relationship in section Radicina.

Table 2.

Morphological comparison of the present species and other Altenraria species in section Radicina

Species Conidia Conidia per chain Medium
Shape Size (μm) Septa
A. atrocariis Ovoid, ellipsoid 50–100×25–38 3–12 1–2 Hosta
A. divaricatae sp. nov. Short-ovoid,subglobose, ellipsoid 21–38×12–26 1–4 1 PCAd
22–39×13–24 1–4 V8Ad
A. carotiincultae Long ovoid or ellipsoid 40–80×15–23 5–7 (–11) 1–3 PCA a
A. chlamydosporifera ellipsoidal or ovoid, occasionally, subglobose 12–41×7–20 1–3(–4) 1, occasionally 2 PCA b
A. glehniae Long ovoid, ellipsoid 20‒40 (–48)×10‒20 3–7 1, occasionally 2 PCA c
A. petroselini Short-ovoid to subsphaeroid 35–62(‒66)×20–26 6–8 1, rarely to 2 PCA a
A. radicina Short-broad or long-narrow ellipsoid and ovoid 42–63×15–20 4–8 1, seldom up to 2 PCA a
A. selini Short-ovoid 32–42(–50)×22–27 3–5 1–3 PCA a
Long-ellipsoid 48–65(–50)×15–20 Up to 7
A. smyrnii Ovoid, obovoid 40–58×18–22 7–8(–10) 1–2 PCA a
Narrower ellipsoid 67–96×13–16
A. vulgarae sp. nov. Short-ovoid, ovoid or long-ellipsoid 25–50 (–70)×16–27 1–5 1 PCAd
24–55 (–77)×13–26 1–8 V8Ad

Alternaria vulgarae L. He & J.X. Deng, sp. nov.

MycoBank No: 838892
Figure 3

Type

China, Hubei Province, Yichang city, Badong county on infected leaves of Foeniculum vulgare. 19 July, 2016, J.X Deng, (YZU-H-0040, holotype), ex-type culture YZU 161234.

Etymology

In reference to the host species name, vulgare.

Description

Colonies on PDA (Fig. 3A) hazel in center and vinaceous buff at the edge, greenish black to mouse gray in reverse, surface velvety or floccose, 79‒82 mm in diam.; On PCA, conidiophores straight or curved, 12–80 × 4–6 μm, 1‒4 transverse septa; conidia solitary arising from the apex or near the apex of the conidiophores or terminal hyphae, rare from lateral of wire-like hyphae, ovoid, short-ovoid or ellipsoid, 25–50 (–70) × 16–27 μm, with 1–5 transverse septa and 1‒4 longitudinal septa (Fig. 3B, C, F); On V8A, conidiophores 24–93 × 4–7 μm, 1‒4 transverse septa, wire-like hyphae up to 200–400 × 4–6 μm; conidia short-ovoid, ovoid, ellipsoid or long-ellipsoid, 24–55 (–77) × 13–26 μm, 1‒8 transverse septa, 1‒4 longitudinal or oblique between septa (Fig. 3D, E, G). There was no secondary conidium production observed on PCA and V8A medium.

Figure 3. 

Morphological characteristics of Alternaria vulgarae (strain: YZU 161234). Colony on PDA for 7 days at 25 °C (A); Sporulation patterns on PCA and V8A (B–E: B, C from V8A D, E from PCA); Conidia from PCA and V8A (F–G). Scale bars: 25 µm (B, C, D, F, G); 50 µm (E).

Additional isolate examined

China, Hubei Province, Yichang city, Badong county on infected leaves of Foeniculum vulgare. 19 July, 2016, L He, living culture YZU 161235.

Notes

Phylogenetic analysis based on combining four gene fragments indicated that Alternaria vulgarae fell in an individual branch in section Radicina of Alternaria and displayed a close relationship with A. petroselini and A. selini with high supported values (Fig. 1). Morphologically, A. vulgarae could be easily distinguished from A. petroselini and A. selini by their sporulation and length of conidiophores. Conidia of A. petroselini were solitary or cluster a small clump with 2‒4 spores near the tips or lateral of conidiophores. Occasionally, the secondary conidium could be observed. Meanwhile, the single conidium or conidial chains (1–3) of A. selini grew from numerous lateral conidiophores, which produced from wire-like hyphae (Simmons 2007). Differently, conidia of A. vulgarae were erected from apex of conidiophores or terminal hyphae. There were no small conidial clumps and secondary conidium formed (Fig. 3B, C, D, E). Moreover, the conidiophores of A. vulgarae (12–80 × 4–6 μm) was longer than A. petroselini (30–60 × 5–6.5 μm) and shorter than A. selini (200–400 × 4–6 μm) (Simmons 2007). Besides, A. vulgarae differed from A. petroselini in conidial shape. Conidium populations of A. petroselini were dominated by shot-ovoid to subsphaerical spores though, the shapes of A. vulgarae were mainly ovoid, ellipsoid or long-ellipsoid (Simmons 2007).

Discussion

Morphologically, Alternaria radicina species-group was one of the 10 subsections (A–1) and comprised 8 species described by Simmons (2007): A. atrocariis, A. carotiincultae, A. japonica, A. petroselini, A. radicina, A. selini, A. smyrnii and A. soliaridae. With the development of molecular studies, the species-group was re-defined and the section Radicina was introduced and perfected (Pryor and Gilbertson 2000; Lawrence et. al 2013; Woudenberg et al. 2013). Uniformly, species in this section had some similar morphological characters, such as conidiophores, sporulation, conidial shape and etc. The phylogenetic analysis showed that only five species were clustered in section Radicina. Except for A. atrocariis, which had no published sequence data, the two other species were shown to belong to other sections: A. japonica felled in the section Japonicae and A. soliaridae formed a separate monophyletic lineage (Woudenberg et al. 2013). Recently, two more species A. chlamydosporifera and A. glehniae were reported in the section Radicina (Marin-Felix et al. 2019; Tao et al. 2019).

In the current study, two new Alternaria species belonged to the section Radicina based on morphological and phylogenetic analysis. Alternaria divaricatae was identified as a novel species based on unique morphological and well-supported phylogenetic analysis (Fig. 2 and Table 2). Phylogenetically, A. vulgarae clustered with A. petroselini and A. selini. Although its phylogenetic position was not well-supported, A. vulgarae can be distinguished from these two species in section Radicina by morphological characteristics (Table 2). Except the length of conidiophores, A. vulgarae was characterized by its sporulation. Meanwhile, A. vulgarae won’t form secondary conidium (Table 2). These characters were important standards to identify Alternaria species (Simmons 2007). And, according to Jeewon and Hyde (2016), a fungal species can be defined based on the distinctive morphological characters even though the phylogenies were not well-supported, because the phylogeny cannot really reflect all morphologies.

Acknowledgments

The financial support of the work was given by the National Natural Science Foundation of China (31400014) and Guangxi Key Laboratory of Biology for Crop Disease and Insect Pests (2019-KF-01).

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