Phylogeny and taxonomy of Golovinomyces orontii revisited

Taxonomy, Phylogeny, and Host Expansion of Powdery Mildew Fungi Parasitic to Veronica Species

Powdery mildew is a prevalent fungal disease that affects various Veronica spp. (Plantaginaceae), caused by species in the genera Podosphaera and Golovinomyces (Erysiphales). There have been recent taxonomic changes in these groups and ongoing disease occurrence on a range of Veronica species previously unrecognized as hosts; however, the pathogen found in Korea remains unidentified. This study aimed to identify the causative agent of powdery mildew on Veronica spp. in Korea through molecular phylogenetic analysis of internal transcribed spacer (ITS) and large subunit (LSU) sequences of rDNA and morphological examination. Our study identified Golovinomyces bolayi as the sole pathogen affecting all nine Veronica species in Korea and confirmed that G. cichoracearum s. str., which was previously identified as the pathogen, was not the causal agent. These results expand the known host range of G. bolayi, including the addition of five Veronica species in Korea: V. hederifolia, V. kiusiana var. glabrifolia, V. longifolia, V. polita, and V. serpyllifolia. Notably, V. kiusiana has been added as a new global host of powdery mildew. These findings substantially enhance our understanding of the taxonomy of powdery mildew pathogens on Veronica species and provide valuable insights into their evolutionary host expansion.

Plant Cell Wall Integrity Perturbations and Priming for Defense

A plant cell wall is a highly complex structure consisting of networks of polysaccharides, proteins, and polyphenols that dynamically change during growth and development in various tissues. The cell wall not only acts as a physical barrier but also dynamically responds to disturbances caused by biotic and abiotic stresses. Plants have well-established surveillance mechanisms to detect any cell wall perturbations. Specific immune signaling pathways are triggered to contrast biotic or abiotic forces, including cascades dedicated to reinforcing the cell wall structure. This review summarizes the recent developments in molecular mechanisms underlying maintenance of cell wall integrity in plant-pathogen and parasitic interactions. Subjects such as the effect of altered expression of endogenous plant cell-wall-related genes or apoplastic expression of microbial cell-wall-modifying enzymes on cell wall integrity are covered. Targeted genetic modifications as a tool to study the potential of cell wall elicitors, priming of signaling pathways, and the outcome of disease resistance phenotypes are also discussed. The prime importance of understanding the intricate details and complete picture of plant immunity emerges, ultimately to engineer new strategies to improve crop productivity and sustainability.

Phylogeny and taxonomy of the genera of Erysiphaceae, part 1: Golovinomyces

Powdery mildews are a monophyletic group of obligate plant pathogenic fungi in the family Erysiphaceae. Powdery mildews are economically important in that they cause damage to many agriculturally significant crops and plants in ecologically important habitats. In this contribution, we introduce a new series of publications focusing on the phylogeny and taxonomy of this group, with an emphasis on specimens collected from North America. The first part of the series focuses on the genus Golovinomyces and includes a section detailing the powdery mildew species concept. We conducted analyses of Golovinomyces spp. with available rDNA sequence data from GenBank and supplemented the data set with rDNA (ITS, 28S, IGS) as well as protein-coding (GAPDH) data from 94 North American collections. Many of the species evaluated are included in phylogenetic and morphological analyses for the first time, including the American species G. americanus, G. brunneopunctatus, G. californicus, G. greeneanus, G. hydrophyllacearum, and G. sparsus. A special emphasis was placed on acquiring ex-type or ex-epitype sequences or presenting reference sequences for phylogenetic-taxonomic purposes. Three new species, G. eurybiarum, G. galiorum, and G. malvacearum, are described, and the new combinations G. fuegianus, G. mutisiae, and G. reginae are introduced. Ex-holotype sequences of Erysiphe sparsa (≡ G. sparsus) reveal that it should be reduced to synonymy with G. ambrosiae, and ex-epitype sequences of G. valerianae reveal that it should be reduced to synonymy with G. orontii. Multiple epitypes are designated with ex-epitype sequences.

A critical revision of the powdery mildew fungi (Erysiphaceae, Ascomycota) of Ukraine: Arthrocladiella and Blumeria

The previously compiled list of species of powdery mildew fungi of Ukraine was published more than 30 years ago. That list included 108 species belonging to 12 genera. However, over the past three decades, numerous changes have been made in the system of the former order Erysiphales, in particular, in its generic composition; moreover, dozens of new species have been described. At the same time, many species of powdery mildew fungi were introduced to Europe, including Ukraine, in particular, from East Asia and North America. Thus, the species composition of powdery mildew fungi of Ukraine has undergone significant changes and requires a critical revision. Therefore, a series of relevant articles is planned to be published. This article, the first in the series, deals with the small genera Arthrocladiella and Blumeria. A list of species of these genera recorded in Ukraine (Arthrocladiella mougeotii, Blumeria avenae, B. bulbigera, B. dactylidis, B. graminicola, B. graminis, and B. hordei), their distribution by regions of Ukraine and a key for identification are provided. Arthrocladiella mougeotii was found to occur occasionally only in nine regions, mainly in the southern part of Ukraine, primarily in the forest-steppe and steppe zones and on the South Coast of Crimea. Blumeria avenae was recorded only in two regions, on the South Coast of Crimea and in Central Polissya and should be also considered rare in Ukraine. The remaining species were observed quite often and registered in 14–24 regions, while B. graminicola and B. graminis are regarded as the most common ones.

Beyond Nuclear Ribosomal DNA Sequences: Evolution, Taxonomy, and Closest Known Saprobic Relatives of Powdery Mildew Fungi (Erysiphaceae) Inferred From Their First Comprehensive Genome-Scale Phylogenetic Analyses

Powdery mildew fungi (Erysiphaceae), common obligate biotrophic pathogens of many plants, including important agricultural and horticultural crops, represent a monophyletic lineage within the Ascomycota. Within the Erysiphaceae, molecular phylogenetic relationships and DNA-based species and genera delimitations were up to now mostly based on nuclear ribosomal DNA (nrDNA) phylogenies. This is the first comprehensive genome-scale phylogenetic analysis of this group using 751 single-copy orthologous sequences extracted from 24 selected powdery mildew genomes and 14 additional genomes from Helotiales, the fungal order that includes the Erysiphaceae. Representative genomes of all powdery mildew species with publicly available whole-genome sequencing (WGS) data that were of sufficient quality were included in the analyses. The 24 powdery mildew genomes included in the analysis represented 17 species belonging to eight out of 19 genera recognized within the Erysiphaceae. The epiphytic genera, all but one represented by multiple genomes, belonged each to distinct, well-supported lineages. Three hemiendophytic genera, each represented by a single genome, together formed the hemiendophytic lineage. Out of the 14 other taxa from the Helotiales, Arachnopeziza araneosa, a saprobic species, was the only taxon that grouped together with the 24 genome-sequenced powdery mildew fungi in a monophyletic clade. The close phylogenetic relationship between the Erysiphaceae and Arachnopeziza was revealed earlier by a phylogenomic study of the Leotiomycetes. Further analyses of powdery mildew and Arachnopeziza genomes may discover signatures of the evolutionary processes that have led to obligate biotrophy from a saprobic way of life. A separate phylogeny was produced using the 18S, 5.8S, and 28S nrDNA sequences of the same set of powdery mildew specimens and compared to the genome-scale phylogeny. The nrDNA phylogeny was largely congruent to the phylogeny produced using 751 orthologs. This part of the study has revealed multiple contamination and other quality issues in some powdery mildew genomes. We recommend that the presence of 28S, internal transcribed spacer (ITS), and 18S nrDNA sequences in powdery mildew WGS datasets that are identical to those determined by Sanger sequencing should be used to assess the quality of assemblies, in addition to the commonly used Benchmarking Universal Single-Copy Orthologs (BUSCO) values.

Current Insight into Traditional and Modern Methods in Fungal Diversity Estimates

Fungi are an important and diverse component in various ecosystems. The methods to identify different fungi are an important step in any mycological study. Classical methods of fungal identification, which rely mainly on morphological characteristics and modern use of DNA based molecular techniques, have proven to be very helpful to explore their taxonomic identity. In the present compilation, we provide detailed information on estimates of fungi provided by different mycologistsover time. Along with this, a comprehensive analysis of the importance of classical and molecular methods is also presented. In orderto understand the utility of genus and species specific markers in fungal identification, a polyphasic approach to investigate various fungi is also presented in this paper. An account of the study of various fungi based on culture-based and cultureindependent methods is also provided here to understand the development and significance of both approaches. The available information on classical and modern methods compiled in this study revealed that the DNA based molecular studies are still scant, and more studies are required to achieve the accurate estimation of fungi present on earth.

Induction of resistance of Podosphaera xanthii (hull-less pumpkin powdery mildew) to triazole fungicides and its resistance mechanism

The aim of this study was to uncover the molecular mechanism through which fungicide resistance develops in Podosphaera xanthii, a fungi that causes powdery mildew in hull-less pumpkin. Treatments of inoculated P. xanthii were carried out on leaves of hull-less pumpkin and subsequently treated with kinds of triazole fungicide for seven generations. Resistant strains of P. xanthii thus obtained were evaluated for their resistance levels. The resistance levels of the fungi to four fungicides of were high except that of the propiconazole-resistant strain, which showed moderate resistance. The F7 generations of five resistant strains thus obtained were cultured continuously for five generations without fungicide induction, and their resistance level were found to be relatively stable. The DNA of the sensitive strain and the five kinds of resistant strains were extracted by the sodium dodecyl sulfate (SDS) method and its internal transcribed spacer (ITS) region was amplified by using ITS1/ITS4 primer and specific primer F/R and they were sequenced respectively. The DNA sequence comparison of resistant and sensitive strains showed that the base pairs of tebuconazole-resistant strains and flusilazole-resistant strains were mutated, with mutation rates of 4.8% and 1.6%, respectively. The base pairs of the other three resistant strains did not change.

Mechanisms of plant cell wall surveillance in response to pathogens, cell wall-derived ligands and the effect of expansins to infection resistance or susceptibility

Cell wall integrity is tightly regulated and maintained given that non-physiological modification of cell walls could render plants vulnerable to biotic and/or abiotic stresses. Expansins are plant cell wall-modifying proteins active during many developmental and physiological processes, but they can also be produced by bacteria and fungi during interaction with plant hosts. Cell wall alteration brought about by ectopic expression, overexpression, or exogenous addition of expansins from either eukaryote or prokaryote origin can in some instances provide resistance to pathogens, while in other cases plants become more susceptible to infection. In these circumstances altered cell wall mechanical properties might be directly responsible for pathogen resistance or susceptibility outcomes. Simultaneously, through membrane receptors for enzymatically released cell wall fragments or by sensing modified cell wall barrier properties, plants trigger intracellular signaling cascades inducing defense responses and reinforcement of the cell wall, contributing to various infection phenotypes, in which expansins might also be involved. Here, we review the plant immune response activated by cell wall surveillance mechanisms, cell wall fragments identified as responsible for immune responses, and expansin's roles in resistance and susceptibility of plants to pathogen attack.

Powdery mildew fungi (Erysiphales, Ascomycota) of Western Polissya of Ukraine

Information on powdery mildew fungi (Erysiphales, Ascomycota) recorded in Western Polissya of Ukraine throughout the history of research in the region is provided. The list included in the article comprises 85 species of 7 genera of Erysiphales, namely 43 species of Erysiphe, 19 of Golovinomyces, 15 of Podosphaera, three of Phyllactinia, two of Neoerysiphe and Sawadaea, and one species of Blumeria. For the first time, 21 species are reported for the region: Erysiphe astragali, E. azaleae, E. howeana, E. hypophylla, E. lycopsidis, E. macleayae, E. prunastri, E. russellii, E. syringae-japonicae, Golovinomyces ambrosiae, G. asterum, G. bolayi, G. fisheri, G. riedlianus, G. verbasci, Neoerysiphe galii, Phyllactinia fraxini, Podosphaera aucupariae, P. phtheirospermi, P. prunicola, and Sawadaea tulasnei. The most common species were Blumeria graminis, Erysiphe alphithoides, E. aquilegiae, E. divaricata, E. ornata, E. polygoni, Podosphaera aphanis, and P. myrtillina. Erysiphe heraclei, Neoerysiphe galeopsidis, and Podosphaera erigerontis-canadensis were recorded quite frequently. Erysiphe arcuata, E. astragali, E. azaleae, E. baeumleri, E. circaeae, E. cruchetiana, E. cruciferarum, E. grosulariae, E. hypophylla, E. lythri, E. macleayae, E. palczewskii, E. penicillata, E. pisi, E. prunastri, E. russellii, E. vanbruntiana, Golovinomyces ambrosiae, G. asterum, G. circumfusus, G. cynoglossi, G. fisheri, G. inulae, G. riedlianus, G. verbasci, Neoerysiphe galii, Phyllactinia fraxini, Ph. guttata s.str., Podosphaera amelanchieris, P. aucupariae, P. balsaminae, P. macularis, P. mors-uvae, P. prunicola, and Sawadaea tulasnei are known from one or two localities, so they are considered as rare species in Western Polissya of Ukraine.

A fungal powdery mildew pathogen induces extensive local and marginal systemic changes in the Arabidopsis thaliana microbiota

Powdery mildew is a foliar disease caused by epiphytically growing obligate biotrophic ascomycete fungi. How powdery mildew colonization affects host resident microbial communities locally and systemically remains poorly explored. We performed powdery mildew (Golovinomyces orontii) infection experiments with Arabidopsis thaliana grown in either natural soil or a gnotobiotic system and studied the influence of pathogen invasion into standing natural multi-kingdom or synthetic bacterial communities (SynComs). We found that after infection of soil-grown plants, G. orontii outcompeted numerous resident leaf-associated fungi while fungal community structure in roots remained unaltered. We further detected a significant shift in foliar but not root-associated bacterial communities in this setup. Pre-colonization of germ-free A. thaliana leaves with a bacterial leaf-derived SynCom, followed by G. orontii invasion, induced an overall similar shift in the foliar bacterial microbiota and minor changes in the root-associated bacterial assemblage. However, a standing root-derived SynCom in root samples remained robust against foliar infection with G. orontii. Although pathogen growth was unaffected by the leaf SynCom, fungal infection caused a twofold increase in leaf bacterial load. Our findings indicate that G. orontii infection affects mainly microbial communities in local plant tissue, possibly driven by pathogen-induced changes in source-sink relationships and host immune status.

First Report of Golovinomyces sonchicola Causing Powdery Mildew on Sonchus oleraceus in Mexico

Sonchus oleraceus, common sow thistle, is native to Europe, Northern Africa, and Western Asia. This plant has become a common weed throughout the world. In Mexico, this weed has become widely naturalized by replacing indigenous plants and invading many agricultural areas. During the spring of 2018 and 2019, common sow thistle plants showing typical symptoms and signs of powdery mildew, were collected from agricultural fields in Ahome, Sinaloa, Mexico. As much as 30% of plants were diseased and 60 to 95% of the foliage was affected. Mycelium was conspicuous and white-gray, and on stems and both surfaces of leaves. Appressoria were nipple-shaped to crenulate. Conidiophores (n= 30) were hyaline, cylindrical, erect, and up to 150 μm long. Foot-cells (n= 30) were distinctly curved, 47 to 75 × 10 to 13 μm, slightly constricted, followed by 1-3 shorter cells and formed conidia in chains. Conidia (n= 100) were ellipsoid to doliiform to subcylindrical, 28 to 37 × 14 to 19 μm, lacked fibrosin bodies, and germinated from the apex. Chasmothecia were not observed. The morphological characters were consistent with those of the anamorphic state of Golovinomyces sonchicola (Braun and Cook 2012, Jakše et al. 2019). A voucher specimen (accession no. FAVF215) was deposited in the Herbarium of the Faculty of Agriculture of El Fuerte Valley at the Autonomous University of Sinaloa (Juan Jose Rios, Sinaloa, Mexico). To confirm the morphological identification, genomic DNA was extracted from mycelium and conidia, and the internal transcribed spacer (ITS) region and part of the 28S gene were amplified by PCR and sequenced. The ITS region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). For amplification of the 28S rRNA partial gene, a nested PCR was performed using the primer sets PM3 (Takamatsu and Kano 2001)/TW14 (Mori et al. 2000) and NL1/TW14 (Mori et al. 2000) for the first and second reactions, respectively. Phylogenetic analyses using the maximum parsimony and maximum likelihood methods (Braun et al. 2019), including ITS and 28S sequences of isolates of Golovinomyces spp. were performed and confirmed the results obtained from the morphological analysis. Isolate FAVF215 grouped in a clade with the other isolates of G. sonchicola. The ITS and 28S sequences were deposited in GenBank under accession numbers MW425872 and MW442972, respectively. Pathogenicity was demonstrated by gently dusting conidia from infected leaves onto leaves of 20 healthy plants and covered with plastic bags for 24 h. Ten non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25 to 35ºC. All inoculated plants developed similar symptoms to those observed in the field from natural infections after 12 days, whereas powdery mildew symptoms and signs were not observed on control plants. The morphology asexual structures of fungus on inoculated plants were identical to those on naturally infected plants, fulfilling Koch's postulates. Inoculation tests were repeated twice with identical results. Based on the morphological data and phylogenetic analysis, the fungus was identified as G. sonchicola. This fungus has been reported causing powdery mildew on S. oleraceus in Germany, The Netherlands, Slovenia, and The United Kingdom (Farr and Rossman 2021). To the best of our knowledge, this is the first report of G. sonchicola causing powdery mildew on S. oleraceus in Mexico. This powdery mildew pathogen may represent an option for the biological control of common sow thistle.

One stop shop IV: taxonomic update with molecular phylogeny for important phytopathogenic genera: 76–100 (2020)

This is a continuation of a series focused on providing a stable platform for the taxonomy of phytopathogenic fungi and fungus-like organisms. This paper focuses on one family: Erysiphaceae and 24 phytopathogenic genera: Armillaria, Barriopsis, Cercospora, Cladosporium, Clinoconidium, Colletotrichum, Cylindrocladiella, Dothidotthia,, Fomitopsis, Ganoderma, Golovinomyces, Heterobasidium, Meliola, Mucor, Neoerysiphe, Nothophoma, Phellinus, Phytophthora, Pseudoseptoria, Pythium, Rhizopus, Stemphylium, Thyrostroma and Wojnowiciella. Each genus is provided with a taxonomic background, distribution, hosts, disease symptoms, and updated backbone trees. Species confirmed with pathogenicity studies are denoted when data are available. Six of the genera are updated from previous entries as many new species have been described.

Australia: A Continent Without Native Powdery Mildews? The First Comprehensive Catalog Indicates Recent Introductions and Multiple Host Range Expansion Events, and Leads to the Re-discovery of Salmonomyces as a New Lineage of the Erysiphales

In contrast to Eurasia and North America, powdery mildews (Ascomycota, Erysiphales) are understudied in Australia. There are over 900 species known globally, with fewer than currently 60 recorded from Australia. Some of the Australian records are doubtful as the identifications were presumptive, being based on host plant-pathogen lists from overseas. The goal of this study was to provide the first comprehensive catalog of all powdery mildew species present in Australia. The project resulted in (i) an up-to-date list of all the taxa that have been identified in Australia based on published DNA barcode sequences prior to this study; (ii) the precise identification of 117 specimens freshly collected from across the country; and (iii) the precise identification of 30 herbarium specimens collected between 1975 and 2013. This study confirmed 42 species representing 10 genera, including two genera and 13 species recorded for the first time in Australia. In Eurasia and North America, the number of powdery mildew species is much higher. Phylogenetic analyses of powdery mildews collected from Acalypha spp. resulted in the transfer of Erysiphe acalyphae to Salmonomyces, a resurrected genus. Salmonomyces acalyphae comb. nov. represents a newly discovered lineage of the Erysiphales. Another taxonomic change is the transfer of Oidium ixodiae to Golovinomyces. Powdery mildew infections have been confirmed on 13 native Australian plant species in the genera Acacia, Acalypha, Cephalotus, Convolvulus, Eucalyptus, Hardenbergia, Ixodia, Jagera, Senecio, and Trema. Most of the causal agents were polyphagous species that infect many other host plants both overseas and in Australia. All powdery mildews infecting native plants in Australia were phylogenetically closely related to species known overseas. The data indicate that Australia is a continent without native powdery mildews, and most, if not all, species have been introduced since the European colonization of the continent.

Multi-locus phylogeny and taxonomy of an unresolved, heterogeneous species complex within the genus Golovinomyces (Ascomycota, Erysiphales), including G. ambrosiae, G. circumfusus and G. spadiceus

Background

Previous phylogenetic analyses of species within the genus Golovinomyces (Ascomycota, Erysiphales), based on ITS and 28S rDNA sequence data, revealed a co-evolutionary relationship between powdery mildew species and hosts of certain tribes of the plant family Asteraceae. Golovinomyces growing on host plants belonging to the Heliantheae formed a single lineage, comprised of a morphologically differentiated complex of species, which included G. ambrosiae, G. circumfusus, and G. spadiceus. However, the lineage also encompassed sequences retrieved from Golovinomyces specimens on other Asteraceae tribes as well as other plant families, suggesting the involvement of a plurivorous species. A multilocus phylogenetic examination of this complex, using ITS, 28S, IGS (intergenic spacer), TUB2 (beta-tubulin), and CHS1 (chitin synthase I) sequence data was carried out to clarify the discrepancies between ITS and 28S rDNA sequence data and morphological differences. Furthermore, the circumscription of species and their host ranges were emended.

Results

The phylogenetic and morphological analyses conducted in this study revealed three distinct species named, viz., (1) G. ambrosiae emend. (including G. spadiceus), a plurivorous species that occurs on a multitude of hosts including, Ambrosia spp., multiple species of the Heliantheae and plant species of other tribes of Asteraceae including the Asian species of Eupatorium; (2) G. latisporus comb. nov. (≡ Oidium latisporum), the closely related, but morphologically distinct species confined to hosts of the Heliantheae genera Helianthus, Zinnia, and most likely Rudbeckia; and (3) G. circumfusus confined to Eupatorium cannabinum in Europe.

Conclusions

The present results provide strong evidence that the combination of multi-locus phylogeny and morphological analysis is an effective way to identify species in the genus Golovinomyces.

Morphophylogenetic analyses revealed that Podosphaera tridactyla constitutes a species complex

Podosphaera tridactyla (s. lat.) is a powdery mildew species occurring on a wide range of Prunus spp. almost worldwide. We have investigated the phylogeny of the Po. tridactyla complex, with special emphasis on potential aspects of cryptic speciation. The results suggested that Po. tridactyla represents a species complex consisting of at least 12 different species. Based on detailed morphological examinations and molecular sequence analyses, we propose dividing Po. tridactyla s. lat. into 10 species, encompassing 7 new species (Po. ampla, Po. pruni-avium, Po. pruni-cerasoidis, Po. prunigena, Po. pruni-lusitanicae, Po. prunina, and Po. pruni-japonicae) and 3 known species (Po. longiseta, Po. salatai, and Po. tridactyla s. str.). Oidium passerinii on Pr. laurocerasus is confirmed as a synonym of Po. tridactyla s. str. Epitypes are designated for Po. tridactyla and Oidium passerinii.

The Lifecycle of the Plant Immune System

Throughout their life span, plants confront an endless barrage of pathogens and pests. To successfully defend against biotic threats, plants have evolved a complex immune system responsible for surveillance, perception, and the activation of defense. Plant immunity requires multiple signaling processes, the outcome of which vary according to the lifestyle of the invading pathogen(s). In short, these processes require the activation of host perception, the regulation of numerous signaling cascades, and transcriptome reprograming, all of which are highly dynamic in terms of temporal and spatial scales. At the same time, the development of a single immune event is subjective to the development of plant immune system, which is co-regulated by numerous processes, including plant ontogenesis and the host microbiome. In total, insight into each of these processes provides a fuller understanding of the mechanisms that govern plant-pathogen interactions. In this review, we will discuss the "lifecycle" of plant immunity: the development of individual events of defense, including both local and distal processes, as well as the development and regulation of the overall immune system by ontogenesis regulatory genes and environmental microbiota. In total, we will integrate the output of recent discoveries and theories, together with several hypothetical models, to present a dynamic portrait of plant immunity.