Characterization of Diaporthe species associated with peach constriction canker, with two novel species from China

Diaporthe species on palms - integrative taxonomic approach for species boundaries delimitation in the genus Diaporthe, with the description of D. pygmaeae sp. nov

The application of traditional morphological and ecological species concepts to closely related, asexual fungal taxa is challenging due to the lack of distinctive morphological characters and frequent cosmopolitan and plurivorous behaviour. As a result, multilocus sequence analysis (MLSA) has become a powerful and widely used tool to recognise and delimit independent evolutionary lineages (IEL) in fungi. However, MLSA can mask discordances in individual gene trees and lead to misinterpretation of speciation events. This phenomenon has been extensively documented in Diaporthe, and species identifications in this genus remains an ongoing challenge. However, the accurate delimitation of Diaporthe species is critical as the genus encompasses several cosmopolitan pathogens that cause serious diseases on many economically important plant hosts. In this regard, following a survey of palm leaf spotting fungi in Lisbon, Portugal, Diaporthe species occurring on Arecaceae hosts were used as a case study to implement an integrative taxonomic approach for a reliable species identification in the genus. Molecular analyses based on the genealogical concordance phylogenetic species recognition (GCPSR) and DNA-based species delimitation methods revealed that speciation events in the genus have been highly overestimated. Most IEL identified by the GCPSR were also recognised by Poisson tree processes (PTP) coalescent-based methods, which indicated that phylogenetic lineages in Diaporthe are likely influenced by incomplete lineage sorting (ILS) and reticulation events. Furthermore, the recognition of genetic recombination signals and the evaluation of genetic variability based on sequence polymorphisms reinforced these hypotheses. New clues towards the intraspecific variation in the common loci used for phylogenetic inference of Diaporthe species are discussed. These results demonstrate that intraspecific variability has often been used as an indicator to introduce new species in Diaporthe, which has led to a proliferation of species names in the genus. Based on these data, 53 species are reduced to synonymy with 18 existing Diaporthe species, and a new species, D. pygmaeae, is introduced. Thirteen new plant host-fungus associations are reported, all of which represent new host family records for Arecaceae. This study has recognised and resolved a total of 14 valid Diaporthe species associated with Arecaceae hosts worldwide, some of which are associated with disease symptoms. This illustrates the need for more systematic research to examine the complex of Diaporthe taxa associated with palms and determine their potential pathogenicity. By implementing a more rational framework for future studies on species delimitation in Diaporthe, this study provides a solid foundation to stabilise the taxonomy of species in the genus. Guidelines for species recognition, definition and identification in Diaporthe are included. Taxonomic novelties: New species: Diaporthe pygmaeae D.S. Pereira & A.J.L. Phillips. New synonyms: Diaporthe afzeliae Monkai & Lumyong, Diaporthe alangii C.M. Tian & Q. Yang, Diaporthe araliae-chinensis S.Y. Wang et al., Diaporthe australiana R.G. Shivas et al., Diaporthe australpacifica Y.P. Tan & R.G. Shivas, Diaporthe bombacis Monkai & Lumyong, Diaporthe caryae C.M. Tian & Q. Yang, Diaporthe chimonanthi (C.Q. Chang et al.) Y.H. Gao & L. Cai, Diaporthe conferta H. Dong et al., Diaporthe diospyrina Y.K. Bai & X.L. Fan, Diaporthe durionigena L.D. Thao et al., Diaporthe etinsideae Y.P. Tan & R.G. Shivas, Diaporthe eucalyptorum Crous & R.G. Shivas, Diaporthe fujianensis Jayaward. et al., Diaporthe fusiformis Jayaward. et al., Diaporthe globoostiolata Monkai & Lumyong, Diaporthe hainanensis Qin Yang, Diaporthe hongkongensis R.R. Gomes et al., Diaporthe hubeiensis Dissan. et al., Diaporthe infecunda R.R. Gomes et al., Diaporthe italiana Chethana et al., Diaporthe juglandigena S.Y. Wang et al., Diaporthe lagerstroemiae (C.Q. Chang et al.) Y.H. Gao & L. Cai, Diaporthe lithocarpi (Y.H. Gao et al.) Y.H. Gao & L. Cai, Diaporthe lutescens S.T. Huang et al., Diaporthe machili S.T. Huang et al., Diaporthe megabiguttulata M. Luo et al., Diaporthe middletonii R.G. Shivas et al., Diaporthe morindae M. Luo et al., Diaporthe nannuoshanensis S.T. Huang et al., Diaporthe nigra Brahman. & K.D. Hyde, Diaporthe orixae Q.T. Lu & Zhen Zhang, Diaporthe passifloricola Crous & M.J. Wingf., Diaporthe pimpinellae Abeywickrama et al., Diaporthe pseudoinconspicua T.G.L Oliveira et al., Diaporthe pungensis S.T. Huang et al., Diaporthe rhodomyrti C.M. Tian & Qin Yang, Diaporthe rosae M.C. Samar. & K.D. Hyde, Diaporthe rumicicola Manawas et al., Diaporthe salicicola R.G. Shivas et al., Diaporthe samaneae Monkai & Lumyong, Diaporthe subcylindrospora S.K. Huang et al., Diaporthe tectonae Doilom et al., Diaporthe tectonigena Doilom et al., Diaporthe theobromatis H. Dong et al., Diaporthe thunbergiicola Udayanga & K.D. Hyde, Diaporthe tuyouyouiae Y.P. Tan et al., Diaporthe unshiuensis F. Huang et al., Diaporthe vochysiae S.A. Noriler et al., Diaporthe xishuangbannaensis Hongsanan & K.D. Hyde, Diaporthe xylocarpi M.S. Calabon & E.B.G. Jones, Diaporthe zaobaisu Y.S. Guo & G.P. Wang, Diaporthe zhaoqingensis M. Luo et al. Citation: Pereira DS, Phillips AJL (2024). Diaporthe species on palms - integrative taxonomic approach for species boundaries delimitation in the genus Diaporthe, with the description of D. pygmaeae sp. nov. Studies in Mycology 109: 487-594. doi: 10.3114/sim.2024.109.08.

Diversity and Virulence of Diaporthe Species Associated with Peach Trunk Diseases in China

Peach (Prunus persica L.) is one of the most important and oldest stone fruits grown in China. Though Diaporthe species have more commonly been reported as plant pathogens, endophytes and saprophytes with a wide range of plant hosts, little is known about the Diaporthe species associated with peach trunk diseases in China. In the present study, forty-four Diaporthe isolates were obtained from trees with peach branch canker, shoot blight and gummosis symptoms in four provinces in China. Based on a combination of morphology and multi-locus sequence analysis of the rDNA internal transcribed spacer region (ITS), calmodulin (cal), translation elongation factor 1-α (tef1) and β-tubulin (tub2), these Diaporthe isolates were assigned to four species. Detailed descriptions and illustrations of all of the species, D. arecae, D. caulivora, D. discoidispora and D. eres, are provided. This study further reports the first host association of D. caulivora and D. discoidispora on peaches worldwide. The pathogenicity experiment results revealed that D. arecae was the most aggressive species, whereas D. discoidispora was the least aggressive on detached peach shoots. This study provides new insights into the fungi associated with peach trunk diseases in China, and the results of this study may help to facilitate routine diagnosis and planning of suitable plant disease management strategies.

Four new endophytic species of Diaporthe (Diaporthaceae, Diaporthales) isolated from Cameroon

The genus Diaporthe (Diaporthaceae, Diaporthales) is a large group of fungi frequently reported as phytopathogens, with ubiquitous distribution across the globe. Diaporthe have traditionally been characterized by the morphology of their ana- and teleomorphic state, revealing a high degree of heterogeneity as soon as DNA sequencing was utilized across the different members of the group. Their relevance for biotechnology and agriculture attracts the attention of taxonomists and natural product chemists alike in context of plant protection and exploitation for their potential to produce bioactive secondary metabolites. While more than 1000 species are described to date, Africa, as a natural habitat, has so far been under-sampled. Several endophytic fungi belonging to Diaporthe were isolated from different plant hosts in Cameroon over the course of this study. Phylogenetic analyses based on DNA sequence data of the internal transcribed spacer region and intervening 5.8S nrRNA gene, and partial fragments of the calmodulin, beta-tubulin, histone and the translation elongation factor 1-α genes, demonstrated that these isolates represent four new species, i.e. D.brideliae, D.cameroonensis, D.pseudoanacardii and D.rauvolfiae. Moreover, the description of D.isoberliniae is here emended, now incorporating the morphology of beta and gamma conidia produced by two of our endophytic isolates, which had never been documented in previous records. Moreover, the paraphyletic nature of the genus is discussed and suggestions are made for future revision of the genus.

Diaporthe species associated with the maritime grass Festuca rubra subsp. pruinosa

Festuca rubra subsp. pruinosa is a perennial grass growing in sea cliffs where plants are highly exposed to salinity and marine winds, and often grow in rock fissures where soil is absent. Diaporthe species are one of the most abundant components of the root microbiome of this grass and several Diaporthe isolates have been found to produce beneficial effects in their host and other plant species of agronomic importance. In this study, 22 strains of Diaporthe isolated as endophytes from roots of Festuca rubra subsp. pruinosa were characterized by molecular, morphological, and biochemical analyses. Sequences of the nuclear ribosomal internal transcribed spacers (ITS), translation elongation factor 1-α (TEF1), beta-tubulin (TUB), histone-3 (HIS), and calmodulin (CAL) genes were analyzed to identify the isolates. A multi-locus phylogenetic analysis of the combined five gene regions led to the identification of two new species named Diaporthe atlantica and Diaporthe iberica. Diaporthe atlantica is the most abundant Diaporthe species in its host plant, and Diaporthe iberica was also isolated from Celtica gigantea, another grass species growing in semiarid inland habitats. An in vitro biochemical characterization showed that all cultures of D. atlantica produced indole-3-acetic acid and ammonium, and the strains of D. iberica produced indole 3-acetic acid, ammonium, siderophores, and cellulase. Diaporthe atlantica is closely related to D. sclerotioides, a pathogen of cucurbits, and caused a growth reduction when inoculated in cucumber, melon, and watermelon.

Diversity of Endophytic Fungi in Annual Shoots of Prunus mandshurica (Rosaceae) in the South of Amur Region, Russia

Prunus mandshurica is a rare species of the Russian Far East; it is cultivated for fruits and as an ornamental tree. The objective was to determine the fungi associated with young shoots of the Manchurian apricot, which is an important biotic factor for plant viability and productivity. Fungi were isolated by incubation of shoot fragments (unsterilized or surface-sterilized) on a growth medium and identified according to their cultural and morphological characteristics. Diaporthe eres and Nothophoma quercina isolates were identified by multilocus phylogenetic analysis (apn2, cal, tef1-α, tub2 for D. eres, and ITS, rpb2, tub2 for N. quercina). In total, 12 species (Alternaria alternata, A. tenuissima, Aureobasidium pullulans, Cladosporium cladosporioides, C. herbarum, D. eres, Epicoccum nigrum, Fusarium graminearum, F. oxysporum, N. quercina, Sarocladium strictum, and Tripospermum myrti) and one genus (Gliocladium sp.) were found. Alternaria alternata, N. quercina, and D. eres were the most frequent species of the shoots. Alternaria tenuissima and F. oxysporum were also frequent in some collections, while all other species were rare or occasional in occurrence. Molecular analysis of D. eres and N. quercina revealed redundancy of some species within the D. eres species complex and the genus Nothophoma. This is the first report on the fungal inhabitants of asymptomatic shoots of P. mandshurica. Nothophoma quercina was identified in Russia for the first time.

First Report of Top Blight of Cunninghamia lanceolata Caused by Diaporthe unshiuensis and Diaporthe hongkongensis in China

Cunninghamia lanceolata (Lamb.) Hook. is an important conifer species widely planted in southern China. A top blight, with an incidence of 20% (40/200 seedlings), occurred on 1-year-old seedlings of C. lanceolata in a nursery, Luzhai, Guangxi, China in August 2021. The disease mainly occurred on shoot tips. The infected needles and shoots appeared brown to brownish red. White conidial tendrils oozed from pycnidia under wet-weather conditions. Lesion margins from fresh samples were cut into small pieces (n=100), which were sterilized according to Mao et al., and placed on potato dextrose agar (PDA) at 25°C. Three isolates (GXJ2, GXJ4, and GXJ6) were obtained and deposited in The China Forestry Culture Collection Center (CFCC 55717, CFCC 55716, and CFCC 55722). The colony of GXJ2 on PDA was white, with sparse aerial mycelia, and became grey with time. The α conidia were fusiform, hyaline, and aseptate, 6.7±0.6 μm × 2.6±0.2 μm (n=30). The β conidia were filiform, hyaline, and curved, 30.4±2.1 μm × 1.4±0.1 μm (n=30). Colonies of GXJ4 and GXJ6 were white, with moderate aerial mycelia, which collapsed at the center, and the collapsed parts were iron-gray. The α conidia were 7.8±0.8 μm × 2.5±0.2 μm (n=30). The β conidia were absent. Morphological characters of 3 isolates matched those of Diaporthe spp.. The partial sequences of ITS, EF1-α, CAL, β-tub, and HIS genes were amplified with primers ITS1/ITS4, EF1-728F/EF1-986R and CAL228F/CAL737R, βt2a/βt2b and CYLH3F/H3-1b according to Gomes et al. 2013, respectively. The sequences for the five genes of each of 3 isolates were deposited in GenBank (Accession Nos. see Supplementary Table 1). BLAST results showed that the ITS, EF1-α, β-tub, HIS, and CAL sequences of GXJ2 were highly similar (>99%) with sequences of Diaporthe unshiuensis, while sequences of GXJ4 and GXJ6 were highly similar (>99%) to those of D. hongkongensis (Supplementary Table 1). Phylogenetic analyses using concatenated sequences placed GXJ2 in the clade of D. unshiuensis, while GXJ4 and GXJ6 in the clade of D. hongkongensis. Based on the phylogeny and morphology, GXJ2 was identified as D. unshiuensis, GXJ4 and GXJ6 as D. hongkongensis. Pathogenicity tests were performed on nine 1-year-old seedlings of C. lanceolata, and 10 needles at shoot tip per seedling were slightly wounded and inoculated with 5-mm mycelial plugs from one of 3 isolates. Three control seedlings were treated with PDA plugs. Each plant was covered with a plastic bag after inoculation and kept in an air-conditioned nursery at 25°C/16°C (day/night). The symptoms appeared 5-8 days after inoculation and were similar to those observed in the nursery. D. unshiuensis and D. hongkongensis were re-isolated from the inoculated seedlings and were confirmed based on morphology and ITS sequences. The controls were symptomless, and no fungus was isolated from them. D. unshiuensis was first reported as an endophyte on the fruit of Citrus unshiu, and caused peach constriction canker, shoot blight of kiwifruit. D. hongkongensis was first described from fruit of Dichroa febrifuga and caused shoot canker of pear, shoot blight and leaf spot of kiwifruit, and fruit rot of peach. This is the first report of D. unshiuensis and D. hongkongensis causing the top blight of C. lanceolata. This study provides a basis for controlling this newly emerging disease in the nursery.

Four new species of Diaporthe (Diaporthaceae, Diaporthales) from forest plants in China

Species of Diaporthe inhabit a wide range of plant hosts as plant pathogens, endophytes and saprobes. During trips to collect forest pathogens in Beijing, Jiangxi, Shaanxi and Zhejiang Provinces in China, 16 isolates of Diaporthe were obtained from branch cankers and leaf spots. These isolates were studied by applying a polyphasic approach including morphological, cultural data, and phylogenetic analyses of the nuclear ribosomal internal transcribed spacer (ITS), calmodulin (cal), histone H3 (his3), partial translation elongation factor-1α (tef-1α) and β-tubulin (tub2) loci. Results revealed four new taxa, D.celticola, D.meliae, D.quercicola, D.rhodomyrti spp. nov. and two known species, D.eres and D.multiguttulata.

Diaporthe species infecting sunflower (Helianthus annuus) in Russia, with the description of two new species

Phomopsis stem canker is economically important sunflower disease that caused by multiple Diaporthe species. Recent investigations resulted in the resolution that there are at least 13 Diaporthe species that can infect sunflower. A comprehensive analysis of the biodiversity and geographic distribution of Diaporthe species in Russia, particularly those that infect sunflower, has not been undertaken. For this study, 16 Diaporthe isolates were obtained from samples of stem canker and visually healthy seeds of Helianthus annuus from northwestern, central European, southern European Russia, North Caucasus, and the Urals in 2016-2019. The aim of this study was to identify these Diaporthe isolates based on morphology and sequence analyses of the nuclear ribosomal internal transcribed spacer (ITS) region, partial calmodulin (cal), DNA-lyase (apn2), histone H3 (his3), translation elongation factor-1α gene (tef1), and ß-tubulin (tub2) genes. The phylogenetic reconstruction revealed well-supported monophyletic clades corresponding to six Diaporthe species: D. eres, D. gulyae, D. helianthi, and D. phaseolorum. Two new species were described: Diaporthe monetii sp. nov. and Diaporthe vangoghii sp. nov. The isolates of D. gulyae and D. phaseolorum collected represent the first records of these species in Russia.

Two new species of Diaporthe (Diaporthaceae, Diaporthales) associated with tree cankers in the Netherlands

Diaporthe (Diaporthaceae, Diaporthales) is a common fungal genus inhabiting plant tissues as endophytes, pathogens and saprobes. Some species are reported from tree branches associated with canker diseases. In the present study, Diaporthe samples were collected from Alnusglutinosa, Fraxinusexcelsior and Quercusrobur in Utrecht, the Netherlands. They were identified to species based on a polyphasic approach including morphology, pure culture characters, and phylogenetic analyses of a combined matrix of partial ITS, cal, his3, tef1 and tub2 gene regions. As a result, four species (viz. Diaporthepseudoalnea sp. nov. from Alnusglutinosa, Diaporthesilvicola sp. nov. from Fraxinusexcelsior, D.foeniculacea and D.rudis from Quercusrobur) were revealed from tree branches in the Netherlands. Diaporthepseudoalnea differs from D.eres (syn. D.alnea) by its longer conidiophores. Diaporthesilvicola is distinguished from D.fraxinicola and D.fraxini-angustifoliae by larger alpha conidia.