Phylogeny and taxonomy of Ophiognomonia (Gnomoniaceae, Diaporthales), including twenty-five new species in this highly diverse genus

Profiling Walnut Fungal Pathobiome Associated with Walnut Dieback Using Community-Targeted DNA Metabarcoding

Walnut dieback can be caused by several fungal pathogenic species, which are associated with symptoms ranging from branch dieback to fruit necrosis and blight, challenging the one pathogen-one disease concept. Therefore, an accurate and extensive description of the walnut fungal pathobiome is crucial. To this end, DNA metabarcoding represents a powerful approach provided that bioinformatic pipelines are evaluated to avoid misinterpretation. In this context, this study aimed to determine (i) the performance of five primer pairs targeting the ITS region in amplifying genera of interest and estimating their relative abundance based on mock communities and (ii) the degree of taxonomic resolution using phylogenetic trees. Furthermore, our pipelines were also applied to DNA sequences from symptomatic walnut husks and twigs. Overall, our results showed that the ITS2 region was a better barcode than ITS1 and ITS, resulting in significantly higher sensitivity and/or similarity of composition values. The ITS3/ITS4_KYO1 primer set allowed to cover a wider range of fungal diversity, compared to the other primer sets also targeting the ITS2 region, namely, GTAA and GTAAm. Adding an extraction step to the ITS2 sequence influenced both positively and negatively the taxonomic resolution at the genus and species level, depending on the primer pair considered. Taken together, these results suggested that Kyo set without ITS2 extraction was the best pipeline to assess the broadest fungal diversity, with a more accurate taxonomic assignment, in walnut organs with dieback symptoms.

Taxonomy and Multigene Phylogeny of Diaporthales in Guizhou Province, China

In a study of fungi isolated from plant material in Guizhou Province, China, we identified 23 strains of Diaporthales belonging to nine species. These are identified from multigene phylogenetic analyses of ITS, LSU, rpb2, tef1, and tub2 gene sequence data coupled with morphological studies. The fungi include a new genus (Pseudomastigosporella) in Foliocryphiaceae isolated from Acer palmatum and Hypericum patulum, a new species of Chrysofolia isolated from Coriaria nepalensis, and five new species of Diaporthe isolated from Juglans regia, Eucommia ulmoides, and Hypericum patulum. Gnomoniopsis rosae and Coniella quercicola are newly recorded species for China.

Morphology and phylogeny of ascomycetes associated with walnut trees (Juglans regia) in Sichuan province, China

In Sichuan province, walnuts, consisting of Juglans regia, Juglans sigillata, and the hybrid J. regia × J. sigillata, are commercially important edible nuts, and J. regia is the most widespread plant. To date, the diversity and distribution of fungi inhabiting on Juglans have not received enough attention, although there have been studies focusing on pathogens from fruit and stem. In order to update the checklist of fungi associated with Sichuan walnuts, a survey on fungi associated with the three Juglans species from 15 representative regions in Sichuan was conducted. In this article, ten fungi distributed in two classes of Ascomycota (Dothideomycetes and Sordariomycetes) were described based on morpho-molecular analyses, and two novel species, Neofusicoccum sichuanense and Sphaerulina juglandina, a known species of Ophiognomonia leptostyla, and seven new hosts or geographical records of Cladosporium tenuissimum, Diatrypella vulgaris, Helminthosporium juglandinum, Helminthosporium velutinum, Loculosulcatispora hongheensis, Periconia byssoides, and Rhytidhysteron subrufulum were included. Morphological descriptions and illustrations of these fungi are provided.

Morphological and Phylogenetic Analyses Reveal Four New Species of Gnomoniopsis (Gnomoniaceae, Diaporthales) from China

The fungal genus Gnomoniopsis (Gnomoniaceae, Diaporthales) has been reported all around the world and isolated from multiple plant hosts. Based on multilocus phylogenies from a combined dataset of internal transcribed spacer (ITS) region, the ribosomal RNA gene cluster, and partial regions of translation elongation factor 1 alpha (tef1) and partial beta-tubulin (tub2), in conjunction with morphological characteristics, we describe and illustrate herein four new species, including Gnomoniopsisdiaoluoshanensis sp. Nov., G. lithocarpi sp. Nov., G. mengyinensis sp. Nov. and G.yunnanensis sp. Nov. Alongside this, their similarity and dissimilarity to morphologically-allied and phylogenetically-related species are annotated and discussed. For facilitating future identification, we update the key to all species currently recognized in this genus.

Morphology and Phylogeny of Gnomoniopsis (Gnomoniaceae, Diaporthales) from Fagaceae Leaves in China

Gnomoniopsis (Gnomoniaceae, Diaporthales) is a well-classified genus inhabiting leaves, branches and fruits of the hosts in three plant families, namely Fagaceae, Onagraceae and Rosaceae. In the present study, eighteen Gnomoniopsis isolates were obtained from diseased leaves of Fagaceae hosts collected from Fujian, Guangdong, Hainan, Henan, Jiangxi and Shaanxi provinces in China. Morphology from the cultures and phylogeny based on the 5.8S nuclear ribosomal DNA gene with the two flanking internally transcribed spacer (ITS) regions, the translation elongation factor 1-alpha (tef1) and the beta-tubulin (tub2) genes were employed to identify these isolates. As a result, seven species were revealed, viz. Gnomoniopsis castanopsidis, G. fagacearum, G. guangdongensis, G. hainanensis, G. rossmaniae and G. silvicola spp. nov, as well as a known species G. daii. In addition, G. daii was firstly reported on the host Quercus aliena.

First report of brown leaf spot on Juglans sigillata caused by Ophiognomonia leptostyla in Sichuan, China

Juglans sigillata Dode (Iron walnut) is mostly distributed in southwestern China, and valued for wood and nuts (Feng et al. 2018). In April 2020, we surveyed a walnut garden located in Baisha Town, Wanyuan City, (Sichuan, China), where brown spot symptoms were observed on leaves of ten trees among of 100 plants, and this disease can result in a reduced growth potential when trees are severely infected. Necrotic and subcircular lesions with conidiamata were observed on diseased leaves. Symptomatic leaves were collected and taken back to the laboratory forfurther analysis. Using the single spore isolation technique developed by Chomnunti et al. (2014), five isolates were grown from the infected leaves on Potato Dextrose Agar medium (PDA). The five isolates had similar colony morphology, which was initially white, suborbicular, gradually turning yellowish with black spots, developing fluffy aerial mycelium. Morphological characteristics were examined using light microscopy on the PDA. Conidiogenous cells were subcylindrical to cylindrical, or ampulliform, hyaline, rarely branched. Macroconidia were lunate, reniform, hyaline, 1-3-septate, mostly 1-septate, distinctly constricted at the septum, the basal cell was bluntly rounded, the apical cell had an acute end, and the basal cell was equal to or larger than the apical cell, measuring 22 to 40.5 × 2.5 to 8.3 μm (mean = 32 × 6.2 μm, n = 50). Microconidia were botuliform, or subfusiform, hyaline, both ends were rounded, straight or curved, aseptate, and measured 10 to 28.5 × 1.9 to 3.7 μm (mean= 17.2 × 2.7 μm, n = 20). A multilocus approach was conducted for precise identification of a representative isolate SICAUCC 20-0012. The internal transcribed spacer regions (ITS), guanine nucleotide-binding protein subunit beta gene (MS204), and translation elongation factor 1-alpha (tef1-α) of isolate SICAUCC 20-0012 were amplified and sequenced as described by Sogonov et al. (2008) and Walker et al. (2012a). GenBank Accession Nos. for ITS, MS204, and tef1-α are MW250303, MW246773, and MW246775, respectively. Phylogenetic analyses showed 100% support with Ophiognomonia leptostyla (Fr.) Sogonov, and the morphology was consistent with the asexual stage of O. leptostyla documented by Walker et al. (2012b). To test Koch's postulates, five healthy plants of J. sigillata (2- to 3-year-old) with 5-8 leaves per plant were inoculated with conidial suspensions (104 conidia/mL) after wounded with a small pin as described by Desai et al. (2019), and the same number of healthy plants were wounded and sprayed with sterile distilled water as controls. Plants were sprayed regularly with distilled water every day and placed in a growth chamber at 25℃ with a 12-h fluorescent light/dark regimen. After 15 days, typical brown spot symptoms developed on inoculated leaves, but not on the controls. The fungus O. leptostyla was reisolated from the lesion as described above but not from non-inoculated leaves. O. leptostyla has been reported on some walnut trees; for example: J. ailantifolia, J. californica, J. cinerea, J. hindsii, J. major, J. mandshurica, J. nigra, and J. regia (Farr & Rossman 2020). However, to our knowledge, this is the first report of O. leptostyla causing brown leaf spot on J. sigillata. J. sigillata is an economically important tree in southwest China, and fungicide treatments should be considered to prevent the spread of this fungus before it becomes more widespread. Chunlin Yang, Yu Deng, and Feihu Wang contributed equally to this work. This research was supported by the Key Research and Development Project of Sichuan Province (2021YFYZ0032).

Molecular reassessment of diaporthalean fungi associated with strawberry, including the leaf blight fungus, Paraphomopsis obscurans gen. et comb. nov. (Melanconiellaceae)

Phytopathogenic fungi in the order Diaporthales (Sordariomycetes) cause diseases on numerous economically important crops worldwide. In this study, we reassessed the diaporthalean species associated with prominent diseases of strawberry, namely leaf blight, leaf blotch, root rot and petiole blight, based on molecular data and morphological characters using fresh and herbarium collections. Combined analyses of four nuclear loci, 28S ribosomal DNA/large subunit rDNA (LSU), ribosomal internal transcribed spacers 1 and 2 with 5.8S ribosomal DNA (ITS), partial sequences of second largest subunit of RNA polymerase II (RPB2) and translation elongation factor 1-α (TEF1), were used to reconstruct a phylogeny for these pathogens. Results confirmed that the leaf blight pathogen formerly known as Phomopsis obscurans belongs in the family Melanconiellaceae and not with Diaporthe (syn. Phomopsis) or any other known genus in the order. A new genus Paraphomopsis is introduced herein with a new combination, Paraphomopsis obscurans, to accommodate the leaf blight fungus. Gnomoniopsis fragariae comb. nov. (Gnomoniaceae), is introduced to accommodate Gnomoniopsis fructicola, the cause of leaf blotch of strawberry. Both of the fungi causing leaf blight and leaf blotch were epitypified. Fresh collections and new molecular data were incorporated for Paragnomonia fragariae (Sydowiellaceae), which causes petiole blight and root rot of strawberry and is distinct from the above taxa. An updated multilocus phylogeny for the Diaporthales is provided with representatives of currently known families.

First Report of Brown Leaf Spot of Juglans hybrid Caused by Ophiognomonia leptostyla in China

"Chuanzao 2" is a walnut variety derived from the hybridization of Juglans regia L. and J. sigillata Dode distributed in southwest China, where it is an economically important tree species in rural regions (Xiao et al. 2012). In April 2020, the variety in a walnut garden showed symptoms of brown leaf spot in Beishan Town (107°21'43.93″E, 31°28'12.34″N), Dazhou City in Sichuan, China, with 5% to 10% of leaves per plant affected (5 plants). Symptomatic leaves showed brown to dark brown spots (2 to 5 mm) with a dark brown to black halo and grayish-tan center. The spots were subcircular to irregular in shape, and gradually expanded and formed necrotic spots. A single conidium isolation was performed (Senanayake et al. 2020) and transferred to Potato Dextrose Agar (PDA). Five isolates were obtained from five different infected leaves. Colonies of five isolates were subcircular, erose or dentate, flat or effuse, white initially, gradually becoming yellowish with white margins, developed and fluffy aerial mycelia, and conidiogenensis was produced underneath mycelia after 25-days-incubation. Conidiogenous cells were subcylindrical to cylindrical, or irregular in shape, and hyaline. Macroconidia were lunate, reniform, hyaline, basal cell bluntly rounded, apical cell with acute end, 1-septate, rarely aseptate, sometimes slightly constricted at septum, basal cell equal or larger than apical cell, and measured 16.5 to 30.5 × 5 to 8.5 μm (mean = 23.2 × 6.3 μm, n = 50). Microconidia were not observed. These morphological characteristics resembled those of Ophiognomonia leptostyla (Fr.) Sogonov (Walker et al. 2012a). For molecular identification, genomic DNA (isolates SICAUCC 21-0008 and SICAUCC 21-0010) was extracted, and the internal transcribed spacers (ITS) region, guanine nucleotide-binding protein subunit beta (MS204) gene, and translation elongation factor 1-alpha (tef1-α) were amplified and sequenced by using the primers ITS5/ITS4 (White et al. 1990), E1F1/E5R1a (Walker et al. 2012a), and EF1-728F/EF1-1567R (Walker et al. 2012b), respectively. Phylogenetic analyses (maximum likelihood) based on a combined dataset showed 100% bootstrap support values in a clade with O. leptostyla. The sequences of ITS, MS204, and tef1-α genes were deposited in GenBank with accession numbers MW493111/MZ026300, MW495270/MZ031975, and MW495271/MZ031974, respectively. To fulfill Koch's postulates, five healthy hybrid plants (2 to 3 years old) with 5 to 8 leaves per plant were spray inoculated with conidium suspensions (104 conidia/mL; isolate SICAUCC 21-0008) prepared from 40-days-old cultures onto the wounded sites via pin-prick inoculation. Similarly, five noninoculated plants sprayed with sterile water served as controls. Plants were placed in a growth chamber at 25℃ on a 12-h fluorescent light/dark regime and daily sprayed with sterile distilled water. After two weeks, observed symptoms were similar to those from natural infections. No disease symptoms were found on control plants. The fungus O. leptostyla was reisolated from the diseased leaves and characterized morphologically. O. leptostyla is a global pathogen and has been reported to cause the leaf spot in many walnut trees, viz. J. ailantifolia, J. californica, J. cinerea, and J. major, etc. To our knowledge, this is the first report of O. leptostyla causing brown leaf spot on Juglans hybrid (J. regia × J. sigillata) in China. The increasing risk of this pathogen in the walnut-growing areas of Sichuan Province of China needs a further exploration and outreach effort to develop effective control measures. Chunlin Yang, Feng Liu, and Qian Zeng contributed equally to this paper.

The genome of the butternut canker pathogen, Ophiognomonia clavigignenti-juglandacearum shows an elevated number of genes associated with secondary metabolism and protection from host resistance responses

Ophiognomonia clavigignenti-juglandacearum (Oc-j) is a plant pathogenic fungus that causes canker and branch dieback diseases in the hardwood tree butternut, Juglans cinerea. Oc-j is a member of the order of Diaporthales, which includes many other plant pathogenic species, several of which also infect hardwood tree species. In this study, we sequenced the genome of Oc-j and achieved a high-quality assembly and delineated its phylogeny within the Diaporthales order using a genome-wide multi-gene approach. We also further examined multiple gene families that might be involved in plant pathogenicity and degradation of complex biomass, which are relevant to a pathogenic life-style in a tree host. We found that the Oc-j genome contains a greater number of genes in these gene families compared to other species in the Diaporthales. These gene families include secreted CAZymes, kinases, cytochrome P450, efflux pumps, and secondary metabolism gene clusters. The large numbers of these genes provide Oc-j with an arsenal to cope with the specific ecological niche as a pathogen of the butternut tree.

Tree inhabiting gnomoniaceous species from China, with Cryphogonomonia gen. nov. proposed

Species of Gnomoniaceae are commonly associated with leaf spot diseases of a wide range of plant hosts worldwide. During our investigation of fungi associated with tree diseases in China, several gnomoniaceous isolates were recovered from symptomatic branches and leaves on different woody plants in the Fagaceae, Pinaceae, and Salicaceae families. These isolates were studied by applying a polyphasic approach including morphological, cultural data, and phylogenetic analyses of partial ITS, LSU, tef1, rpb2 and tub2 gene sequences. As a result, three species were identified with characters fitting into the family Gnomoniaceae. One of these species is described herein as Cryphognomonia pini gen. et sp. nov., characterized by developed pseudostromata and ascospores with obvious hyaline sheath; Gnomoniopsis xunwuensis sp. nov. is illustrated showing sympodially branched conidiophore, oval or fusiform conidia; and one known species, Plagiostoma populinum. The current study improves the understanding of gnomoniaceous species causing diebacks and leaf spot on ecological and economic forest trees.

Taxonomy of two synnematal fungal species from Rhus chinensis, with Flavignomonia gen. nov. described

Rhuschinensis represents a commercially and ecologically important tree species in China, but suffers from canker diseases in Jiangxi Province. Synnemata, pycnidia and ascomata were discovered on cankered tissues. Strains were obtained from single ascospore or conidium within the fruiting bodies and identified based on morphological comparison and the phylogenetic analyses of partial ITS, LSU, tef1 and rpb2 gene sequences. As a result, two species were confirmed to represent two kinds of synnemata. One of these species is described herein as Flavignomoniarhoigenagen. et sp. nov.; and Synnemasporellaaculeans is illustrated showing ascomata, pycnidia and synnemata. Flavignomonia is distinguished from Synnemasporella by the colour of the synnematal tips. Additionally, Flavignomonia can be distinguished from the other gnomoniaceous genera by the formation of synnemata.

Reassessment of Paragnomonia (Sydowiellaceae, Diaporthales) and typification of Paragnomonia fragariae, the cause of strawberry root rot and petiole blight

Paragnomonia fragariae is a plant pathogenic ascomycete causing root rot and petiole blight of perennial strawberry in northern Europe. This paper provides a revised description of Paragnomonia and P. fragariae with lecto- and epitypification based on the species original description, recent collections from four European countries, examination of specimens used in the previous taxonomic studies and phylogenetic analyses of DNA sequences of LSU, ITS/5.8S and tef1-α. This study presents the first report of P. fragariae on cultivated strawberry in Finland and Lithuania. Our study on growth rate showed that P. fragariae is a cold-adapted fungus growing almost equally at 5 °C as at 20 °C and attaining maximal growth at 15 °C. New primers were designed for amplification of ca. 0.8 kb fragment of tef1-α of Sydowiella fenestrans. Additionally, newly generated sequences of tef1-α were obtained for the first time from 21 isolates of seven species belonging to five genera of Sydowiellaceae, including the type species S. fenestrans, therefore considerably contributing to the current knowledge on phylogenetic relationships of this insufficiently studied group of fungi. The phylogenetic analysis has also revealed that the recently described species "S." centaureii is genetically distant from the generic type S. fenestrans and other Sydowiella.

Phylogenetic relationships of Phaeochorella parinarii and recognition of a new family, Phaeochorellaceae (Diaporthales)

Species of Phaeochorella are biotrophic leaf parasites with a tropical distribution, traditionally accepted in the family Phyllachoraceae, Phyllachorales in classifications based on morphological characters. Phylogenetic evidence presented here resolves the relationship of Phaeochorella within the Sordariomycetes, based on a multilocus analysis of partial nuc rDNA large subunit (28S) and internal transcribed spacers (ITS1-5.8S-ITS2 = ITS), the DNA-directed RNA polymerase II second largest subunit (RPB2), and the translation elongation factor 1-α (TEF1-α) gene. Phylogenetic analyses indicate that Phaeochorella belongs to the Diaporthales rather than the Phyllachorales. Phaeochorella parinarii, the type species of the genus, present on native hosts from the Brazilian Cerrado, forms a unique clade with a species of Phaeoappendicospora with high support. Thus, a new family, Phaeochorellaceae, Diaporthales, including both genera, is herein proposed. With the exception of P. parinarii and P. zonata, all other species in Phaeochorella (P. artocarpi, P. ciliata, P. machaerii) were excluded from the genus.

New species and records of Coryneum from China

Following the abandonment of dual nomenclature and the implementation of single-name nomenclature for pleomorphic fungi, Coryneum was considered to have priority over Pseudovalsa and was recommended for use. Currently, Coryneum is the only genus in the family Coryneaceae (Diaporthales). However, DNA sequence data are lacking for most Coryneum species, and no detailed phylogenetic analyses of the genus are yet available. In the present study, fresh Coryneum samples were collected from chestnut (Castanea) and oak (Quercus) trees in China and morphologically compared with accepted Coryneum species. Based on morphological characteristics, they were identified as one known species, Coryneum castaneicola, and three novel species described here as C. gigasporum, C. sinense, and C. suttonii. Conidial dimensions and host association were considered major characters for species distinction. The previously unknown sexual morph of C. castaneicola is reported and described. A phylogenetic analysis of nuc rDNA internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) and large subunit (28S) sequence data of a representative matrix of Diaporthales confirmed Coryneaceae to represent a monophyletic clade. A phylogenetic analysis of a combined sequence matrix containing the ITS-28S rDNA, the translation elongation factor 1-α (TEF1α), and the second largest subunit of the RNA polymerase II (RPB2) of the four Chinese and four additional European Coryneum species was performed, confirming the distinctness of these novel species.

Common Cutaneous Bacteria Isolated from Snakes Inhibit Growth of Ophidiomyces ophiodiicola

There is increasing concern regarding potential impacts of snake fungal disease (SFD), caused by Ophidiomyces ophiodiicola (Oo), on free-ranging snake populations in the eastern USA. The snake cutaneous microbiome likely serves as the first line of defense against Oo and other pathogens; however, little is known about microbial associations in snakes. The objective of this study was to better define the composition and immune function of the snake cutaneous microbiome. Eight timber rattlesnakes (Crotalus horridus) and four black racers (Coluber constrictor) were captured in Arkansas and Tennessee, with some snakes exhibiting signs of SFD. Oo was detected through real-time qPCR in five snakes. Additional histopathological techniques confirmed a diagnosis of SFD in one racer, the species' first confirmed case of SFD in Tennessee. Fifty-eight bacterial and five fungal strains were isolated from skin swabs and identified with Sanger sequencing. Non-metric multidimensional scaling and PERMANOVA analyses indicated that the culturable microbiome does not differ between snake species. Fifteen bacterial strains isolated from rattlesnakes and a single strain isolated from a racer inhibited growth of Oo in vitro. Results shed light on the culturable cutaneous microbiome of snakes and probiotic members that may play a role in fighting an emergent disease.

Pseudodidymellaceae fam. nov.: Phylogenetic affiliations of mycopappus-like genera in Dothideomycetes

The familial placement of four genera, Mycodidymella, Petrakia, Pseudodidymella, and Xenostigmina, was taxonomically revised based on morphological observations and phylogenetic analyses of nuclear rDNA SSU, LSU, tef1, and rpb2 sequences. ITS sequences were also provided as barcode markers. A total of 130 sequences were newly obtained from 28 isolates which are phylogenetically related to Melanommataceae (Pleosporales, Dothideomycetes) and its relatives. Phylogenetic analyses and morphological observation of sexual and asexual morphs led to the conclusion that Melanommataceae should be restricted to its type genus Melanomma, which is characterised by ascomata composed of a well-developed, carbonaceous peridium, and an aposphaeria-like coelomycetous asexual morph. Although Mycodidymella, Petrakia, Pseudodidymella, and Xenostigmina are phylogenetically related to Melanommataceae, these genera are characterised by epiphyllous, lenticular ascomata with well-developed basal stroma in their sexual morphs, and mycopappus-like propagules in their asexual morphs, which are clearly different from those of Melanomma. Pseudodidymellaceae is proposed to accommodate these four genera. Although Mycodidymella and Xenostigmina have been considered synonyms of Petrakia based on sexual morphology, we show that they are distinct genera. Based on morphological observations, these genera in Pseudodidymellaceae are easily distinguished by their synasexual morphs: sigmoid, multi-septate, thin-walled, hyaline conidia (Mycodidymella); globose to ovoid, dictyosporus, thick-walled, brown conidia with cellular appendages (Petrakia); and clavate with a short rostrum, dictyosporus, thick-walled, brown conidia (Xenostigmina). A synasexual morph of Pseudodidymella was not observed. Although Alpinaria was treated as member of Melanommataceae in a previous study, it has hyaline cells at the base of ascomata and pseudopycnidial, confluent conidiomata which is atypical features in Melanommataceae, and is treated as incertae sedis.

Families of Diaporthales based on morphological and phylogenetic evidence

Diaporthales is an important ascomycetous order comprising phytopathogenic, saprobic, and endophytic fungi, but interfamilial taxonomic relationships are still ambiguous. Despite its cosmopolitan distribution and high diversity with distinctive morphologies, this order has received relativelyiaceae, Macrohilaceae, Melanconidaceae, Pseudoplagiostomaceae, Schizoparmaceae, Stilbosporaceae and Sydowiellaceae. Taxonomic uncertainties among genera are also clarified and recurrent discrepancies in the taxonomic position of families within the Diaporthales are discussed. An updated outline and key to families and genera of the order is presented.