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Research Article
Two novel species and a new host record of Alternaria (Pleosporales, Pleosporaceae) from sunflower (Compositae) in Myanmar
expand article infoZin Mar Nwe, Khin Nayyi Htut§, Sein Lai Lai Aung, Ya-Nan Gou, Cheng-Xin Huang, Jian-Xin Deng
‡ Yangtze University, Jingzhou, China
§ Yezin Agricultural University, Nay Pyi Taw, Myanmar
Open Access

Abstract

Sunflower (Helianthus annuus L.) is a widely cultivated, fast-growing crop known for its seeds and oil, with substantial ecological and economic importance globally. However, it faces challenges from leaf diseases caused by Alternaria species, which threaten its yield. Three small-spored Alternaria species were isolated from leaf spot and blight symptoms on sunflower in Myanmar. All the species were determined based on morphological characterization and a multi-locus phylogenetic assessment of seven genes, including the internal transcribed spacer of rDNA region (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase second largest subunit (RPB2), translation elongation factor 1-α (TEF1), Alternaria major allergen gene (Alt a 1), endopolygalacturonase gene (EndoPG), and an anonymous gene region (OPA10-2). The results introduced two new Alternaria species, A. myanmarensis sp. nov. and A. yamethinensis sp. nov., and a known species of A. burnsii, firstly reported from sunflower.

Key words

Alternaria, morphology, new host record, novel species, phylogeny

Introduction

The genus Alternaria Nees, 1816, which belongs to the family Pleosporaceae, order Pleosporales, and phylum Ascomycota, is a widely distributed dematiaceous fungus frequently found in plants, soil, food, and indoor air environments (Thomma 2003). It includes more than 790 species epithets, and approximately 382 species have been accepted (Hongsanan et al. 2020; Wijayawardene et al. 2020; Gannibal et al. 2022; Li et al. 2023; Liao et al. 2023). The identification and classification of Alternaria commonly rely on cultural features, conidial characteristics (shape, size, septation, beak formation), sporulation patterns, and hosts (Zhang 2003; Simmons 2007; Yu 2015). Normally, Alternaria is categorized into two obviously distinct groups: large-spored and small-spored Alternaria (Simmons 2007). The conidial bodies of large-spored species typically measure 60–100 μm in length and the small-spored species are less than 60 μm. The morphological criteria can be influenced by growth conditions, including substrate, light, and humidity, potentially undermining their reliability in characterizing the genus (Woudenberg et al. 2013).

Nowadays, diverse molecular techniques have been utilized to clarify the variability among and within Alternaria species (Lawrence et al. 2016). The classification has been significantly informed through phylogenetic analysis by utilizing more than ten distinct genetic loci. These loci include the regions of rDNA (nuclear small subunit (SSU), large subunit (LSU), and internal transcribed spacer (ITS)), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase second largest subunit (RPB2), translation elongation factor 1-α (TEF1), Alternaria major allergen (Alt a 1), endopolygalacturonase (EndoPG), an anonymous genomic region (OPA10-2), calmodulin (CAL), and eukaryotic orthologous groups (KOG) (Liu et al. 2024). The genus is found to encompass 29 sections through comprehensive multi-locus phylogenetic analyses (Ghafri et al. 2019; Gannibal et al. 2022). Among them, the section Alternaria, which includes members with catenate and small-spored conidia, is recognized as having only 11 phylogenetic species and one species complex (Woudenberg et al. 2015).

Leaf spot and blight disease on sunflower (Helianthus annuus L.) caused by Alternaria significantly decreases head diameters and seed production (Kgatle et al. 2020). Sunflower, belonging to the Compositae family and native to North America, is an oilseed crop cultivated worldwide, with its oil ranking as the second most important source of edible vegetable oils (Zhang et al. 2021). The plant is also commercialized for livestock feed (Yegorov et al. 2019). It was introduced to Myanmar in 1968 (Favre and Myint 2009) and covered 0.224 million hectares with a yield of 9245 kg/ha in 2022 (http://faostat.fao.org/site/567/default.aspx#ancor). In the Central Dry Zone of Myanmar (Mandalay, Sagaing, and Magway Regions), it contributes to more than 77% of the overall oilseed crop production (DOA 2020). During the monsoon season in 2023, three small-spored Alternaria species were isolated from leaf symptoms of sunflower collected in a plantation in Mandalay, Myanmar. In this study, those species were meticulously identified and illustrated through morphological and phylogenetic approaches.

Materials and methods

Sample collection and fungal isolation

In August 2023, sunflower leaves displaying spot and blight symptoms were randomly collected from plantations in Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E). From each field, samples were randomly collected at five different points, placed in separate clean zip bags and transported to the laboratory. For fungal isolation, leaf fragments from the edges of the lesions were excised, treated with a 1% sodium hypochlorite solution for three minutes, rinsed three times with distilled water, plated on moist filter papers in Petri dishes and then incubated at 25 °C in the dark for sporulation. A single spore was picked using a sterile glass needle under a stereomicroscope and inoculated onto potato dextrose agar (PDA: Difco, Montreal, Canada). Once sufficiently grown, pure cultures were isolated by a single spore and preserved in test tube slants at 4 °C in the Fungi Herbarium at Yangtze University (YZU) in Jingzhou, Hubei, China. MycoBank numbers were obtained by following the protocols outlined on (https://www.mycobank.org/).

Morphological characterization

To study the characteristics of the culture, mycelial plugs (6 mm diameter) were extracted from the periphery of 5-day-old colonies growing on PDA, transferred to fresh 90 mm PDA plates, and incubated in darkness at 25 °C for 7 days. For the examination of conidial morphology, mycelia were cultured on V8 juice agar (V8A) and potato carrot agar (PCA) under white fluorescent light at 22 °C with an 8-hour light/16-hour dark period (Simmons 2007). After a 7-day incubation period, the sporulation patterns and conidial characteristics were determined under an ECLIPSE Ni-U microscopic system (Nikon, Japan). The conidia were observed using a lactophenol-picric acid solution. Fifty randomly selected conidia were recorded.

DNA extraction, PCR amplification, and Sequencing

Genomic DNA extraction involved scraping fresh mycelia from colonies cultivated on PDA for 5 days at 25 °C, following the method outlined by Watanabe et al. (2010). Polymerase chain reaction (PCR) amplification and sequencing targeted specific genes of the internal transcribed spacer region of rDNA (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase second largest subunit (RPB2), translation elongation factor 1-α (TEF1), Alternaria major allergen (Alt a 1), endopolygalacturonase gene (EndoPG), and an anonymous genomic region (OPA10-2). In the PCR processes, a 25 μL reaction mixture was prepared, consisting of 21 μL of 1.1× Taq PCR Star Mix (TSINGKE), 2 μL of template DNA, and 1 μL of each primer. The amplification reaction was performed using a Bio-Rad T100 thermocycler according to the conditions listed in (Table 1). The generated products underwent electrophoresis in a 1% agarose gel and were visualized by UV transillumination. Subsequently, the amplified products were purified and sequenced in both directions, facilitated by TSINGKE Company (Beijing, China). Initially, sequences from both ends were examined and manually edited using BioEdit v. 7.0.9 (Hall 1999). Following this, the sequences were aligned and further edited with the PHYDIT v3.2 software (Chun 1995) before being submitted to GenBank (https://www.ncbi.nlm.nih.gov/) (Table 2).

Table 1.

Primers and PCR protocols.

Gene regions Primers PCR conditions References
ITS ITS5/ITS4 94 °C for 3 min, 34 cycles of 94 °C for 30 s, 55 °C for 30 s and 72 °C for 2 min, 72 °C for 10 min White et al. 1990
GAPDH gpd1/gpd2 95 °C for 2 min, 32 cycles of 95 °C for 30 s, 56 °C for 30 s and 72 °C for 42 s, 72 °C for 5 min Berbee et al. 1999
RPB2 RPB2-5F/ RPB2-7cR 94 °C for 5 min, 34 cycles of 94 °C for 45 s, 57 °C for 45 s and 72 °C for 1 min, 72 °C for 10 min Sung et al. 2007
TEF1 EF1-728F/ EF1-986R 94 °C for 3 min, 35 cycles of 94 °C for 30 s, 55 °C for 45 s and 72 °C for 1 min, 72 °C for 10 min Carbone and Kohn et al. 1999
Alt a 1 Alt-for/ Alt-rev 94 °C for 2 min, 33 cycles of 94 °C for 30 s, 60 °C for 30 s and 72 °C for 30 s, 72 °C for 10 min Hong et al. 2005
EndoPG PG3/ PG2b 94 °C for 3 min, 33 cycles of 94 °C for 30 s, 50 °C for 30 s and 72 °C for 59 s, 72 °C for 5 min Andrew et al. 2009
OPA10-2 OPA10-2L/ OPA10-2R 94 °C for 2 min, 33 cycles of 94 °C for 30 s, 56 °C for 30 s and 72 °C for 30 s, 72 °C for 10 min Andrew et al. 2009
Table 2.

The GenBank accession numbers of Alternaria strains used in the present study.

Species Strain Host/Substrate Country GenBank accession numbers
ITS GAPDH TEF1 RPB2 Alt a 1 Endo-PG OPA10-2
A. alternantherae CBS 124392 Solanum melongena China KC584179 KC584096 KC584633 KC584374 KP123846
A. alternata CBS 916.96T Arachis hypogaea India AF347031 AY278808 KC584634 KC584375 AY563301 JQ811978 KP124632
CBS 102604 Minneola tangelo Israel KP124334 AY562410 KP125110 KP124802 AY563305 KP124035 KP124643
CBS 102596 Citrus jambhiri USA KP124328 KP124183 KP125104 KP124796 KP123877 KP124030 KP124637
CBS 918.96 Dianthus chinensis UK AF347032 AY278809 KC584693 KC584435 AY563302 KP124026 KP124633
CBS 106.34 Linum usitatissimum Unknown Y17071 JQ646308 KP125078 KP124771 KP123853 KP124000 KP124608
CBS 121547 Pyrus bretschneideri China KP124372 KP124224 KP125150 KP124842 KP123920 KP124076 KP124685
CBS 101.13 Peat soil Switzerland KP124392 KP124244 KP125170 KP124862 KP123940 KP124096 KP124705
CBS 126.60 Wood UK KP124397 KP124249 KP125175 KP124867 JQ646390 KP124101 KP124710
CBS 109730 Solanum lycopersicum USA KP124399 KP124251 KP125177 KP124869 KP123946 KP124103 KP124713
CBS 119545T Senecio skirrhodon New Zealand KP124409 KP124260 KP125187 KP124879 KP123956 KP124113 KP124723
A. baoshanensis MFLUCC 21-0124T Curcubita moschata China MZ622003 OK236706 OK236613 OK236659 OK236760
MFLUCC 21-0296 C. moschata China MZ622004 OK236707 OK236612 OK236660 OK236759
A. betae-kenyensis CBS 118810 T Beta vulgaris var. cicla Kenya KP124419 KP124270 KP125197 KP124888 KP123966 KP124123 KP124733
A. breviconidiophora MFLUCC 21-0786T Digitalis sp. Italy MZ621997 OK236698 OK236604 OK236651 OK236751
A. burnsii CBS 118817 Tinospora cordifolia India KP124424 KP124274 KP125202 KP124893 KP123971 KP124128 KP124738
CBS 118816 Rhizophora mucronata India KP124423 KP124273 KP125201 KP124892 KP123970 KP124127 KP124737
CBS 130264 Human sputum India KP124425 KP124275 KP125203 KP124894 KP123972 KP124129 KP124739
CBS 879.95 Sorghum sp. UK KP124422 KP124272 KP125200 KP124891 KP123969 KP124126 KP124736
CBS 107.38T Cuminum cyminum India KP124420 JQ646305 KP125198 KP124889 KP123967 KP124124 KP124734
CBS 108.27 Gomphrena globosa Unknown KC584236 KC584162 KC584727 KC584468 KP123850 KP123997 KP124605
YZU 191042 Allium cepa Myanmar MN656137 MN718663 MN656147 MN656155 MN656142
YZU 191003 A. cepa Myanmar MN656136 MN718662 MN656146 MN656154 MN656141
YZU 231748 Helianthus annuus Myanmar OR888998 OR963608 OR979650 PP116480 OR979653 OR979659 PP034180
YZU 231747 H. annuus Myanmar OR888996 OR963607 OR979649 PP116479 OR979652 OR979658 PP034179
A. falcata MFLUCC 21-0123 Atriplex sp. Italy MZ621992 OK236599 OK236693 OK236649 OK236746
A. eichhorniae CBS 489.92T Eichhornia crassipes India KC146356 KP124276 KP125204 KP124895 KP123973 KP124130 KP124740
A. ellipsoidialis MFLUCC 21-0132 Eupatorium cannabinum Italy MZ621989 OK236596 OK236690 OK236643 OK236743
A. eupatoriicola MFLUCC 21-0122 E. cannabinum Italy MZ621982 OK236683 OK236589 OK236636 OK236736
A. gaisen CBS 632.93R Pyrus pyrifolia Japan KC584197 KC584116 KC584658 KC584399 KP123974 AY295033 KP124742
CBS 118488R P. pyrifolia Japan KP124427 KP124278 KP125206 KP124897 KP123975 KP124132 KP124743
A. gossypina CBS 102597 Minneola tangelo USA KP124432 KP124281 KP125211 KP124902 KP123978 KP124137 KP124748
CBS 104.32T Gossypium sp. Zimbabwe KP124430 JQ646312 KP125209 KP124900 JQ646395 KP124135 KP124746
A. iridiaustralis CBS 118486T Iris sp. Australia KP124435 KP124284 KP125214 KP124905 KP123981 KP124140 KP124751
CBS 118487 Iris sp. Australia KP124436 KP124285 KP125215 KP124906 KP123982 KP124141 KP124752
YZU 161003 Iris ensata China MG601454 MG601454 MG601456 MG601457
A. jacinthicola CBS 133751T Eichhornia crassipes Mali KP124438 KP124287 KP125217 KP124908 KP123984 KP124143 KP124754
CBS 878.95 Arachis hypogaea Mauritius KP124437 KP124286 KP125216 KP124907 KP123983 KP124142 KP124753
A. koreana SPL2-1T Atractylodes ovata Korea LC621613 LC621647 LC621715 LC621681 LC631831 LC631844 LC631857
SPL2-4 A. ovata Korea LC621615 LC621649 LC621717 LC621683 LC631832 LC631845 LC631858
A. longipes CBS 121333R Nicotiana tabacum USA KP124444 KP124293 KP125223 KP124914 KP123990 KP124150 KP124761
CBS 540.94 N. tabacum USA AY278835 AY278811 KC584667 KC584409 AY563304 KP124147 KP124758
A. minimispora MFLUCC 21-0127T Citrullus lanatus Thailand MZ621980 OK236587 OK236681 OK236634 OK236734
A. muriformispora MFLUCC 21-0784T Plantago sp. Italy MZ621976 OK236677 OK236583 OK236630 OK236730
A. myanmarensis sp. nov. YZU 231735 Helianthus annuus Myanmar OR888993 OR963611 OR979651 PP508255 OR979656 OR979662 PP034183
YZU 231736T H. annuus Myanmar OR897031 OR963612 OR963615 PP508256 OR979657 OR979663 PP034184
A. orobanches MFLUCC 21-0137T Orobanche sp. Italy MZ622007 OK236710 OK236763
MFLUCC 21-0303 Orobanche sp. Italy MZ622008 OK236711 OK236764
A. ovoidea MFLUCC 21-0782T Dactylis glomerata Italy MZ622005 OK236708 OK236614 OK236661
MFLUCC 21- 0298 D. glomerata Italy MZ622006 OK236709 OK236615 OK236662
A. obpyriconidia MFLUCC 21-0121T Vicia faba Italy MZ621978 OK236585 OK236680 OK236633 OK236732
A. phragmiticola MFLUCC 21-0125T Phragmites sp. Italy MZ621994 OK236696 OK236602 OK236649 OK236749
A. rostroconidia MFLUCC 21-0136T Arabis sp. Italy MZ621969 OK236670 OK236576 OK236623 OK236723
A. silicicola MFLUCC 22-0072T Salix alba Russia MZ621999 OK236700 OK236606 OK236653 OK236753
A. tomato CBS 114.35 Solanum lycopersicum Unknown KP124446 KP124295 KP125225 KP124916 KP123992 KP124152 KP124763
CBS 103.30 S. lycopersicum Unknown KP124445 KP124294 KP125224 KP124915 KP123991 KP124151 KP124762
A. torilis MFLUCC 14-0433T Torilis arvensis Italy MZ621988 OK236594 OK236688 OK236641 OK236741
A. yamethinensis sp. nov. YZU 231738 Helianthus annuus Myanmar OR888995 OR963609 OR963613 PP179252 OR979654 OR979660 PP034181
YZU 231739T H. annuus Myanmar OR889008 OR963610 OR963614 PP179253 OR979655 OR979661 PP034182

Phylogenetic analysis

The resulting sequences were processed in the GenBank database at the National Center for Biotechnology Information (NCBI) using BLAST searches. The relevant sequences were downloaded and derived from newly reported sequences of recent publications (Woudenberg et al. 2015; Luo et al. 2018; Htun et al. 2022; Li et al. 2022, 2023; Romain et al. 2022) used in the present analysis (Table 2). The adjustments, alignments, and comparative analyses of the gene sequences were executed using ClustalX (Larkin et al. 2007) within the MEGA 11 software platform (Tamura et al. 2021) and gaps were treated as missing data. Maximum-likelihood (ML) and Bayesian inference (BI) methods were utilized to elucidate the phylogenetic relationships among Alternaria species. The ML analyses were constructed using the GTRGAMMAI model of nucleotide evolution, and 1000 bootstrap (BS) replicates were performed to assess branch support with RAxML v. 7.0.3 (Stamatakis et al. 2008). Bayesian analysis was conducted with MrBayes v.3.2.6 (Ronquist et al. 2012) with the best-fit model of nucleotide substitution, GTR+I+G, determined by MrModeltest v.2.3 (Posada and Crandall 1998) with the Akaike Information Criterion (AIC). The “MrModelblock” file in MrModeltest was run using both the PAUP path (Swofford 2002) and the MrMt path (Nylander 2004). The two simultaneous Markov Chain Monte Carlo (MCMC) algorithms were launched from random trees, covering 106 generations, with data collected every 100 generations (Rannala and Yang 1996). The analysis was stopped when the standard deviation of split frequencies dropped below 0.01. A burn-in parameter of 25% was established, signifying that 75% of the trees were retained during the burn-in phase, with the remaining trees utilized for calculating the posterior probabilities in the majority-rule consensus tree. Subsequently, the phylogenetic tree was visualized and modified using FigTree v. 1.4.3 (Rambaut 2016). In the phylogram, branch support is indicated by (posterior probability PP/bootstrap value BS) equal to or above 0.6/60%.

Results

Phylogenetic analyses

The combined dataset, comprising sequences from seven gene loci (ITS, GAPDH, RPB2, TEF1, Alt a 1, EndoPG, and OPA10-2), included 59 Alternaria strains, containing the present 6 strains. It had 2,722 characters with gaps, allocated as follows: 466 characters for ITS, 302 for GAPDH, 307 for RPB2, 216 for TEF1, 421 for Alt a1, 391 for EndoPG, and 619 for OPA10-2. The phylogenetic tree was constructed and rooted using Alternaria alternantherae CBS 124392 as the outgroup. The Maximum Likelihood (ML) phylogeny was used as the foundational tree. Four strains fell into two independent clades and two, YZU 231747 and YZU 231748, were clustered with the strains of known species A. burnsii (Fig. 1). One of the individual clades comprising YZU 231738 and YZU 231739, with PP/BS values of 1.0/100% was found to be sister to A. betae-kenyensis, A. eichhorniae, A. iridiaustralis, and A. salicicola. It also fell into a subclade with A. eichhorniae and A. betae-kenyensis (PP/BS=1.0/85%). Another clade, consisting of YZU 231735 and YZU 231736, exhibited PP/BS values of 0.98/96%, falling into a group with A. orobanches, A. koreana, and A. ovoidea, which is highly supported by PP/BS values of 1.0/94%. Additionally, the strains YZU 231747 and YZU 231748 were clustered with the previously reported A. burnsii strains. They also formed a subclade with a strain from Myanmar, YZU 191003, supported by PP/BS values of 0.98/65% (Fig. 1). The results indicated that the current strains represented two new species and a known species of Alternaria, all belonging to the section Alternaria.

Figure 1. 

Phylogenetic tree generated from maximum likelihood analyses using aligned ITS, GAPDH, RPB2, TEF1, Alt a 1, EndoPG, and OPA10-2 gene sequences of the present Alternaria strains and their related species. Bootstrap support (BS) values ≥ 60% and Bayesian posterior probability (PP) scores ≥ 0.60 were shown at the nodes (ML/PP). Alternaria alternantherae CBS 124392 was used as an outgroup. Type strains are marked ‘T’. Representative strains are marked ‘R’. The strains from the present study are highlighted in bold.

Taxonomy

Alternaria myanmarensis M.N. Zin & J.X. Deng, sp. nov.

MycoBank No: 853961
Fig. 2

Etymology

The specific epithet refers to the location, Myanmar.

Holotype

Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E), collected from infected leaves of Helianthus annuus in August 2023 by Khin Nayyi Htut (YZU–H–2023154, holotype). Ex-type culture (YZU 231736) was also obtained.

Description

Colonies on PDA are circular, light vinaceous buff with a white halo at the edge, velvety, cottony, honey to white in reverse, 68–70 mm in diameter (Fig. 2a). On PCA, conidiophores arise directly from lateral or apical aerial hyphae or medium, lightly flexuous, sometimes geniculate at the apex, 27.5–85(–90) × 2–4.5 μm, conidia emerge from the apex or geniculate loci, short to long ellipsoid or narrow-ovoid,10–30(–42) × 7–11 μm, 2–5 transverse septa, 2–6 units per chain, beak 3–12 μm (Fig. 2c, e, g). On V8A, conidiophores arise from near the apex of the terminal hyphae, 24–65(–70) × 3–5 μm, conidia 8–29(–33) × 3–14 μm, 2–5 transverse septa, 3–6 units per chain, beak 1–9 μm (Fig. 2b, d, f).

Figure 2. 

Morphology of Alternaria myanmarensis sp. nov. from Helianthus annuus: Colony on PDA for 7 days at 25 °C (a); Sporulation patterns on V8A (b) and on PCA (c); Conidiophores on V8A (d) and on PCA (e); Conidia on V8A (f) and on PCA (g) at 22 °C. Scale bars: 50 μm (b, c); 25 μm (d–g).

Additional isolate examined

Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E) from the infected leaves of Helianthus annuus, August 2023, Khin Nayyi Htut, living cultures (YZU 231735).

Notes

This species is phylogenetically grouped with A. koreana, A. orobanches, and A. ovoidea, based on sequences from ITS, GAPDH, RPB2, TEF1, Alt a 1, EndoPG, and OPA10-2 genes. It is distinct from A. koreana and A. ovoidea in its smaller conidial body size, particularly in width, and its sporulation patterns which produce catenulate conidia up to 6 units on PCA and V8A media, rather than those of the two closely related species (up to 2 units) on SNA and PDA (Table 3).

Table 3.

Morphological comparison of the present Alternaria and their relevant species.

Species Conidia Conidia per chain Medium References
Shape Body (μm) Beak (μm) Septa
A. burnsii Ovoid or ellipsoid 30–50 × 9–13 5–8 Short chain Host Simmons (2007)
Narrow-ovoid or narrow-ellipsoid 30–40 × 8–14 Beakless 3–7 PCA , V8A Simmons (2007)
Narrow ovoid or ellipsoid 20–50 × 8–15 3–30 4–7 5–9 PCA Htun et al. (2020)
Ovoid or ellipsoid, tapering beak 1642 (–50) × 515 230 (–40) 26 26 PCA This study
955 (–65) × 712 223 (–35) 26 29 V8A This study
A. tomato Ellipsoid to long-ovoid 39–65 × 13–22 60–105 × 2 6–9 Solitary Host Simmons (2007)
A. myanmarensis sp. nov. Short to long ellipsoid or narrow-ovoid 1030 (–42) × 711 312 25 26 PCA This study
829 (–33) × 314 19 25 36 V8A This study
A. koreana Short to long ovoid 12.9–61.2 × 8.6–20.7 2–7 1–2 SNA Romain et al. (2022)
A. ovoidea Ovoid 48–65 × 15.5–30 1–3 Solitary PDA Li et al. (2022)
A. orobanches Obclavate to ovoid 20–50 × 10–20 3–6 1–2 PCA Li et al. (2023)
A. yamethinensis sp. nov. Narrow ovoid or Subellipsoid, blunt-pointed 1750 (–65) × 814 515 × 26 27 26 PCA This study
3257 (–63) × 815 1.58 × 14 27 29 V8A This study
A. betae-kenyensis Ovoid or subellipsoid 20–28 × 8–10 5–7 15–25 PCA Simmons (2007)
A. eichhorniae Narrow ovoid or subellipsoid, with a blunt-pointed or rounded apical cell 50–70 × 12–18 50–150 × 4–5 7–9 1–2 V8A Simmons (2007)
A. iridiaustralis Ovoid and short broad ellipsoid 30–40 × 16–24 3–4 3–5 PCA Simmons (2007)
Ellipsoid or long ellipsoid 20–50 × 15–24 15–100(–133) × 3.5–4.5 1–4 1–2 PCA Luo et al. (2018)
A. salicicola Straight or curved, subglobose to obclavate or obpyriform 10–50 × 12–38 1–6 At least 2 PCA Li et al. (2023)

Alternaria yamethinensis M.N. Zin & J.X. Deng, sp. nov.

MycoBank No: 851391
Fig. 3

Etymology

The epithet designation is attributed to the Yamethin township, which was the location where the holotype was originally collected.

Holotype

Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E) on infected leaves of Helianthus annuus, August 2023, Khin Nayyi Htut, (YZU–H–2023154, holotype), ex-type culture (YZU 231739).

Description

Colonies on PDA are light yellow in the center, white at the edge, with flocculent hyphae, and sulfur yellow to pure yellow in reverse, 38–50 mm in diameter (Fig. 3a). On PCA, conidiophores arise from the substrate, are simple, straight or flexuous, septate, light to brown, 19–85 (–95) × 3–6.5 μm. Conidia arise from the apex or near the apex of the conidiophores, rarely from lateral hyphae, and are narrow ovoid or subellipsoid, blunt-pointed, 17–50 (–65) × 8–14 µm, with 2–7 transverse septa and 2–6 units per chain with a beak 5–15 µm (Fig. 3c, e, g). On V8A, conidiophores are 17–65 (–85.5) × 2–5.5 μm, and conidia are 32–57 (–63) × 8–15 µm with 2–7 transverse septa, 2–9 units per chain and a beak 1.5–8 µm (Fig. 3b, d, f).

Figure 3. 

Morphology of Alternaria yamethinensis sp. nov. from Helianthus annuus: Colony on PDA for 7 days at 25 °C (a); Sporulation patterns on V8A (b) and on PCA (c); Conidiophores on V8A (d) and on PCA (e); Conidia on V8A (f) and on PCA (g) at 22 °C. Scale bars: 50 μm (b, c); 25 μm (d–g).

Additional isolate examined

Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E) on infected leaves of Helianthus annuus, August 2023, Khin Nayyi Htut, living culture (YZU 231738).

Notes

Phylogenetic analysis based on combined gene regions of ITS, GAPDH, RPB2, TEF1, Alt a 1, EndoPG, and OPA10-2, along with morphological characteristics, clearly separates this species from others. It can be differentiated from A. betae-kenyensis (20–28 × 8–10 µm) by conidial size, A. eichhorniae (50–150 × 4–5 µm) and A. iridiaustralis (15–100(–133) × 3.5–4.5 µm) by conidial beak, and A. salicicola (12–38 µm) by conidial body width. Moreover, it is significantly distinct from those four species by conidial units per chain (Table 3).

Alternaria burnsii Uppal, Patel & Kamat, Indian J.Agric.Sci.8:61 (1938)

MycoBank No: 259164
Fig. 4

Description

Colonies on PDA are dark, surface buff to honey, cottony to vinaceous buff, with a united margin, measuring 62–64 mm in diameter (Fig. 4a). On PCA, conidiophores are single, arising laterally from hyphae, and are either straight or curved, 15–110(–115) × (3–5.5) μm. Conidia emerge from the apex and are ovoid or ellipsoid with a tapering beak, 16–42(–50) × 5–15 μm, with 2–6 transverse septa, 2–6 in a chain, and beaks are 2–30(–40) μm (Fig. 4c, e, g). On V8A, conidiophores 12–95(–103) × (2–4) μm, conidia 9–55(–65) × 7–12 μm, and 2–6 transverse septa, 2–9 in a chain, beaks 2–23(–35) μm (Fig. 4b, d, f).

Figure 4. 

Morphology of Alternaria burnsii from Helianthus annuus: Colony on PDA for 7 days at 25 °C (a); Sporulation patterns on V8A (b) and on PCA (c); Conidiophores on V8A (d) and on PCA (e); Conidia on V8A (f) and on PCA (g) at 22 °C. Scale bars: 50 μm (b, c); 25 μm (d–g).

Additional isolate examined

In Myanmar, Mandalay Region, Yamethin Township, Segyi Village (30°21'28.188"N, 112°08'32.136"E), samples showing disease symptoms on Helianthus annuus were collected in August 2023 by Khin Nayyi Htut. The living culture is designated as YZU 231747.

Notes

A. burnsii has been found in many countries on different hosts and substrates. The host range of A. burnsii is reported to include Apiaceae: Cuminum cyminum (Uppal et al. 1938), Bunium persicum (Mondal et al. 2002), Apium graveolens (Zhang 2003; Zhuang 2005), Cumin (Shekhawat et al. 2013); Cucurbitaceae: Cucurbita maxima (Paul et al. 2015), Triticum aestivum and Phoenix dactylifera (Al-Nadabi et al. 2018), Coconut (Sunpapao et al. 2022), Phoenix dactylifera (Al-Nadabi et al. 2020); Liliaceae: Allium cepa (Htun et al. 2022), and Orchidaceae: Bletilla striata (Yin et al. 2023). In the present study, A. burnsii was firstly reported from Helianthus annuus in Myanmar. Phylogenetically, the present strains fall into a sub-branch with A. burnsii YZU 191003 from Allium cepa reported in Myanmar with consistent morphology and nucleotide sequences of ITS, GAPDH, RPB2, TEF1, and Alt a 1, gene regions (Htun et al. 2022) (Fig. 1).

Discussion

In this study, two new small-spored species, Alternaria myanmarensis sp. nov. and A. yamethinensis sp. nov., and a known species of A. burnsii were identified and illustrated based on morphology and phylogenetic analyses. Molecular research has demonstrated significant separation between large- and small-spored Alternaria species (Peever et al. 2004; Hong et al. 2005). The taxonomy of small-spored Alternaria species has faced controversies because they exhibit similar morphological characteristics (Wang et al. 2021). Molecular-based assays could facilitate the correct identification alongside morphological traits (Woudenberg et al. 2015; Lawrence et al. 2016). However, molecular analysis has encountered difficulties because the section Alternaria could not be clearly determined using standard markers due to minimal or no variation (Andrew et al. 2009; Prencipe et al. 2023). Previous studies indicated that the identifying criteria of small-spored Alternaria become significant only when utilizing a combination of different genes (Woudenberg et al. 2015; Zhang et al. 2023). Agreeing with Romain et al. (2022), the present species are also clearly distinguished based on a multigene sequence analysis, indicating which species belong to the section Alternaria. To date, this section includes more than 91 species, according to recent publications (Gannibal and Lawrence (2016); Nishikawa and Nakashima (2020); Gou et al. 2022, 2023; Li et al. 2023; Liao et al. 2023; He et al. 2024).

Phylogenetically, A. myanmarensis sp. nov. and A. yamethinensis sp. nov. fall into individual lineages representing new taxa. A. myanmarensis sp. nov. is characterized by small conidial body (10–30(–42) × 7–11 μm) catenating in a longer chain (2 to 6 units), compared with its relevant species (solitary or 2 conidia in a chain), A. koreana from Atractylodes ovata in Korea (Romain et al. 2022), A. orobanches from Orobanche sp. in Italy (Li et al. 2023) and A. ovoidea from Dactylis glomerata in Italy (Li et al. 2022). Morphologically, A. yamethinensis sp. nov. (conidial width 8–14 μm and 2–6 conidial units per chain) is quite different from its closely related species of A. iridiaustralis (conidial width 15–24 μm) from Iris spp. (Luo et al. 2018), A. salicicola (conidial width 12–38 μm) from Salix alba in Russia (Li et al. 2023), A. betae-kenyensis (15 to 25 conidial units per chain) from Beta vulgaris in Kenya (Simmons 2007) and A. eichhorniae (solitary or two conidia in a chain) from Eichhornia crassipes in India (Simmons 2007). Additionally, either RPB2 or OPA10-2 region serves as great marker for the delimitation of the above species.

The genus Alternaria ranks 10th among fungal genera for infecting over 4,000 plant species (Thomma 2003). The first record of Alternaria helianthi (named Helminthosporium helianthi) on sunflower in Uganda was done by Hansford (1943). Later, 12 more species were found in various sunflower-growing countries globally, including A. helianthinficiens (Simmons 1986), A. leucanthemi (Carson 1987), A. longissima (Prathuangwong et al. 1991), A. carthami (Chowdhury 1994), A. zinniae (Bhutta et al. 1997), A. alternata (Lagopodi and Thanassoulopoulos 1998), A. protenta (Cho and Yu 2000), A. heliophytonis (Simmons 2007), A. roseogrisea (Roberts 2008), A. helianthicola (Rajender et al. 2016), A. tenuissima (Wang et al. 2019), and A. solani and A. tomatophila (Zhang et al. 2021). However, it has been established that Alternaria helianthi, which is the synonym of Alternariaster helianthi, was based on morphology and phylogeny (Simmons 2007; Wei et al. 2022). In this study, three Alternaria species associated with sunflower in Myanmar have been identified, and pathogenicity tests reveal that these present Alternaria species are causal pathogens for sunflower, of which A. yamethinensis sp. nov. is identified as the most pathogenic one (Suppl. material 1). This discovery underscores the importance of Alternaria leaf spot and blight on sunflower and helps in disease management in Myanmar.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

The study was funded by the National Natural Science Foundation of China (32270022).

Author contributions

The conception and design of the study were a joint effort by all authors involved. Sample collection was done by Khin Nayyi Htut. Jian-Xin Deng provided crucial scientific oversight throughout both the laboratory and fieldwork. Zin Mar Nwe initiated the fungal isolation and led the research, with support in data analysis from Sein Lai Lai Aung, Ya-Nan Gou, and Cheng-Xin Huang. Zin Mar Nwe drafted the manuscript, which was refined through critical feedback from all authors. Jian-Xin Deng played a pivotal role in supervising the finalization of the manuscript, with all authors giving their approval to the completed work.

Author ORCIDs

Zin Mar Nwe https://orcid.org/0009-0000-6376-8306

Khin Nayyi Htut https://orcid.org/0009-0009-9498-8040

Sein Lai Lai Aung https://orcid.org/0009-0006-2738-5598

Ya-Nan Gou https://orcid.org/0009-0005-1740-4065

Cheng-Xin Huang https://orcid.org/0000-0001-7770-5242

Jian-Xin Deng https://orcid.org/0000-0001-7304-5603

Data availability

All of the data that support the findings of this study are available in the main text or Supplementary Information.

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Supplementary material

Supplementary material 1 

Diseased symptoms of Helianthus annuus caused by Alternaria spp.

Zin Mar Nwe, Khin Nayyi Htut, Sein Lai Lai Aung, Ya-Nan Gou, Cheng-Xin Huang, Jian-Xin Deng

Data type: doc

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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