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Scanning electron micrographs of Melampsora uredinial paraphyses and aeciospores. The most common shape for uredinial paraphyses is seen in A. In B are unevenly verrucose aeciospores of Melampsora phylotype 'N' from Tsuga heterophylla.
Source publication
In North America Melampsora rusts that parasitize willows (Salix species) have never been adequately studied and mostly have been referred to a collective species, Melampsora epitea (Kunze & Schm.) Thüm, of European origin. Even taxa that are nominally distinct from M. epitea, such as M. abieti-caprearum and M. paradoxa, currently are considered to...
Context in source publication
Context 1
... they were distinct (FIG. 4B). Shallow pits were observed at the base of spines of uredinio- spores in some cases (FIG. 4C). Ear-shaped paraphy- ses (FIG. 4D), which were often more peripheral than interspersed in uredinia, were evident in some collections, particularly from S. piperi. However more typically paraphyses were pear-or lollipop-shaped (FIG. 5A) and interspersed throughout uredinia. Some uredinia from leaves of S. sitchensis and S. boothii were characterized by a relatively high ratio of paraphyses to urediniospores. To our knowledge aeciospores of M. epitea f. sp. tsugae have not been examined previously under SEM; we illustrated (FIG. 5B) the unevenly verrucose aeciospores ...
Citations
... infecting willow (Ziller, 1974). Recent studies based on morphology and ribosomal DNA sequences have revealed that M. epitea is a species complex (Smith et al., 2004;Bennett et al., 2011;Kenaley et al., 2014;Zhao et al., 2017). In total, 12-14 phylotypes were recognized in North America (Smith et al., 2004), and more recently, Zhao et al. (2017) have described 13 species based on specimens collected from East Asia. ...
... In total, 12-14 phylotypes were recognized in North America (Smith et al., 2004), and more recently, Zhao et al. (2017) have described 13 species based on specimens collected from East Asia. These groups are differentiated based on aecial hosts, subtle morphological differences in the urediniospores, uredinia and telia, and ribosomal DNA sequences (Smith et al., 2004;Bennett et al., 2011;Kenaley et al., 2014;Zhao et al., 2017). Morphology and host associations are important characters in making an identification, but within this group, this information must be supplemented with DNA sequence data to arrive at the best possible identification. ...
... The specimens housed in these herbaria were all identified based on morphology and host associations. Identifying the causal agent of rust disease on willows based on morphology is difficult due to the similarity of key characteristics (Ziller, 1974), and recent DNA-based studies have suggested that M. epitea is far more complex than revealed by morphological examination (Smith et al., 2004;Bennett et al., 2011;Kenaley et al., 2014;Zhao et al., 2017). Having these specimens available for research will be an important resource for any future studies related to understanding the composition of the M. epitea complex in Canada. ...
In June, 2021, laurel willow ( Salix pentandra ) near Slave Lake, Alberta, was found to be infected by a Melampsora sp. that produced bright yellow urediniospores in uredia that were present on catkins, leaves, and stems. All Melampsora species previously reported in Canada are recorded as infecting leaves; therefore, further investigation was undertaken to ascertain the identity of this pathogen. To assess the relationship between this specimen and other Melampsora spp. previously collected from Canada, samples of willow leaves infected by Melampsora spp. were sourced from mycological herbariums located at the Laurentian Forestry Centre (QFB) and the Northern Forestry Centre (CFB, WINF(M)). DNA sequence data from the internal transcribed spacer (ITS) ribosomal RNA region of the fresh specimen, herbarium specimens, and DNA sequence data deposited within GenBank, were used to conduct a phylogenetic analysis. Sequencing and BLAST analysis of the material from the sample resulted in a 99.3% sequence identity match to Melampsora epitea “Mel J” collected from Larix laricina in New York State. The ITS sequence from the herbarium sample WINF(M)7356 (described as M. abieti-capraearum from Manitoba) had 100.0% identity with the Alberta sample. Additionally, specimens WINF(M)11892 ( Melampsora sp. from Manitoba) and CFB8931 ( Melampsora sp. from the Yukon) had 99.0% sequence identity with the Alberta sample. From these results we applied the identity of M. epitea to the rust discovered in Slave Lake, AB. With the current emphasis on willows for bioenergy production in Canada, growers must remain vigilant for this pathogen and the damages it could cause to willow plantations.
... While much has been learned about willow leaf rust over the past decades [11,32,33], no study has specifically investigated the transcriptomes of M. americana and S. purpurea shortly after inoculation. This project uses 3′ RNA-seq to investigate the post-inoculation expression profiles in resistant and susceptible progeny in a S. purpurea F 2 mapping population [25], as well as in the pathogen, M. americana. ...
Background
Melampsora spp. rusts are the greatest pathogen threat to shrub willow (Salix spp.) bioenergy crops. Genetic resistance is key to limit the effects of these foliar diseases on host response and biomass yield, however, the genetic basis of host resistance has not been characterized. The addition of new genomic resources for Salix provides greater power to investigate the interaction between S. purpurea and M. americana, species commonly found in the Northeast US. Here, we utilize 3′ RNA-seq to investigate host-pathogen interactions following controlled inoculations of M. americana on resistant and susceptible F2S. purpurea genotypes identified in a recent QTL mapping study. Differential gene expression, network analysis, and eQTL mapping were used to contrast the response to inoculation and to identify associated candidate genes.
Results
Controlled inoculation in a replicated greenhouse study identified 19 and 105 differentially expressed genes between resistant and susceptible genotypes at 42 and 66 HPI, respectively. Defense response gene networks were activated in both resistant and susceptible genotypes and enriched for many of the same defense response genes, yet the hub genes of these common response modules showed greater mean expression among the resistant plants. Further, eight and six eQTL hotspots were identified at 42 and 66 HPI, respectively. The combined results of three analyses highlight 124 candidate genes in the host for further analysis while analysis of pathogen RNA showed differential expression of 22 genes, two of which are candidate pathogen effectors.
Conclusions
We identified two differentially expressed M. americana transcripts and 124 S. purpurea genes that are good candidates for future studies to confirm their role in conferring resistance.
... Several studies have uncovered a great number of rust species complexes and cryptic species. For example, 14 different phylogenetic species were determined in the Melampsora epitea complex [8]. Similar patterns of cryptic speciation have also been in the rust species Endoraecium digitatum and Dasyspora gregaria [9][10][11]. ...
Chrysomyxa rusts are fungal pathogens widely distributed in the Northern hemisphere, causing spruce needle and cone rust diseases, and they are responsible for significant economic losses in China. Taxonomic delimitation and precise species identification are difficult within this genus because some characters often overlap in several species. Adequate species delimitation, enhanced by the use of DNA-based methodologies, will help to establish well-supported species boundaries and enable the identification of cryptic species. Here, we explore the cryptic species diversity in the rust genus Chrysomyxa from China. Species delimitation analyses are conducted using a distance-based method (ABGD) and three tree-based methods (GMYC, bPTP, and mPTP) based on combined LSU and ITS sequences of over 60 specimens. Although there is some incongruence among species delimitation methods, two new species and three putative cryptic species are identified. The key to 20 Chrysomyxa species distributed in China is presented. These results suggest that a significant level of undiscovered cryptic diversity is likely to be found in Chrysomyxa from China. Future studies should consider multiple analytical methods when dealing with multi-locus datasets.
... Although it has been used for species delimitation of some groups (Weber et al. 2002;Szabo 2006;Chatasiri et al. 2006;Alaei et al. 2009), the ITS region is not an effective barcode for rust fungi; intra-specific and intra-individual variation are observed in a wide range of taxa potentially misleading identification, but it is also difficult to amplify without rustspecific primers and the presence of indels inhibits direct sequencing (McTaggart and Aime 2018). The LSU has been used as an alternative barcode for rust fungi instead, alone or with other markers (e.g., Bennett et al. 2011;McTaggart et al. 2015a;Maier et al. 2016;Ebinghaus et al. 2018). Depending on the genus, different barcodes may provide better species resolution (see discussion in Bubner et al. 2019). ...
... Thorough molecular revisions are needed at the species level, based on phylogenetic analysis of the ITS2-LSU region (McTaggart and Aime 2018) and in combination with secondary barcodes, as some studies of rust fungi have uncovered a great number of species complexes and cryptic species. For example, analyses of the Melampsora epitea complex from northwestern North America determined the existence of 14 different phylogenetic species (also termed "phylotypes") within this single morphospecies (Bennett et al. 2011) and studies within the Endoraecium digitatum (Berndt 2011) and Dasyspora gregaria (Beenken et al. 2012) species complexes have revealed similar patterns of cryptic speciation. It is recommended to evaluate the suitability of already existing names when describing new species. ...
Species delimitation is one of the most fundamental processes in biology. Biodiversity undertakings, for instance, require explicit species concepts and criteria for species delimitation in order to be relevant and translatable. However, a perfect species concept does not exist for Fungi. Here, we review the species concepts commonly used in Basidiomycota, the second largest phylum of Fungi that contains some of the best known species of mushrooms, rusts, smuts, and jelly fungi. In general, best practice is to delimitate species, publish new taxa, and conduct taxonomic revisions based on as many independent lines of evidence as possible, that is, by applying a so-called unifying (or integrative) conceptual framework. However, the types of data used vary considerably from group to group. For this reason we discuss the different classes of Basidiomycota, and for each provide: (i) a general introduction with difficulties faced in species recognition, (ii) species concepts and methods for species delimitation, and (iii) community recommendations and conclusions.
... While much has been learned about willow leaf rust over the past decades (11,32,33), no study has speci cally investigated the transcriptomes of M. americana and S. purpurea shortly after inoculation. This project uses 3' RNA-seq to investigate the post-inoculation expression pro les in resistant and susceptible progeny in a S. purpurea F 2 mapping population (25), as well as in the pathogen, M. ...
Background: Melampsora spp. rusts are the greatest pathogen threat to shrub willow (Salix spp.) bioenergy crops. Genetic resistance is key to limit the effects of these foliar diseases on host response and biomass yield, however, the genetic basis of host resistance has not been characterized. The addition of new genomic resources for Salix provides greater power to investigate the interaction between S. purpurea and M. americana, species commonly found in the Northeast US. Here, we utilize 3' RNA-seq to investigate host-pathogen interactions following controlled inoculations of M. americana on resistant and susceptible F2 S. purpurea genotypes identified in a recent QTL mapping study. Differential gene expression, network analysis, and eQTL mapping was used to contrast the response to inoculation and to identify associated candidate genes.
Results: Controlled inoculation in a replicated greenhouse study identified 19 and 105 differentially expressed genes between resistant and susceptible genotypes at 42 and 66 HPI, respectively. Defense response gene networks were activated in both resistant and susceptible genotypes and enriched for many of the same defense response genes, yet the hub genes of these common response modules showed greater mean expression among the resistant plants. Further, eight and six eQTL hotspots were identified at 42 and 66 HPI, respectively. The combined results of the three analyses highlight 124 candidate genes in the host for further analysis while analysis of pathogen RNA showed differential expression of 22 genes, two of which are candidate pathogen effectors.
Conclusions: We identified two differentially expressed M. americana transcripts and 124 S. purpurea genes that are good candidates for future studies to confirm their role in conferring resistance.
... Within the Kingdom Fungi, there is an incredible diversity that cannot be perceived through morphology. Cryptic species are being uncovered in Agaricomycetes (e.g., Stefani et al. 2014;Sánchez-García et al. 2016), Lecanoromycetes (e.g., Singh et al. 2015), Leotiomyces (e.g., Grünig et al. 2008), Pucciniomycetes (Bennett et al. 2011), Ustilaginomycetes (e.g., Li et al. 2017), and other major clades. And while the Laboulbeniales has been the subject of a large-scale study to estimate the global species richness of the group (Weir and Hammond 1997), cryptic diversity was not part of the equation. ...
In this paper we present an updated checklist of thallus-forming Laboulbeniomycetes (Ascomycota, Pezi-zomycotina), that is, the orders Herpomycetales and Laboulbeniales, from Belgium and the Netherlands. Two species are newly described based on morphology, molecular data (ITS, LSU ribosomal DNA) and ecology (host association). These are Hesperomyces halyziae on Halyzia sedecimguttata (Coleoptera, Coc-cinellidae) from both countries and Laboulbenia quarantenae on Bembidion biguttatum (Coleoptera, Car-abidae) from Belgium. In addition, nine new country records are presented. For Belgium: Laboulbenia aubryi on Amara aranea (Coleoptera, Carabidae) and Rhachomyces spinosus on Syntomus foveatus (Co-leoptera, Carabidae). For the Netherlands: Chitonomyces melanurus on Laccophilus minutus (Coleoptera, Dytiscidae), Euphoriomyces agathidii on Agathidium laevigatum (Coleoptera, Leiodidae), Laboulbenia fas-ciculata on Omophron limbatum (Coleoptera, Carabidae), Laboulbenia metableti on Syntomus foveatus and S. truncatellus (Coleoptera, Carabidae), Laboulbenia pseudomasei on Pterostichus melanarius (Coleoptera, Carabidae), Rhachomyces canariensis on Trechus obtusus (Coleoptera, Carabidae), and Stigmatomyces hydrel-liae on Hydrellia albilabris (Diptera, Ephydridae). Finally, an identification key to 140 species of thallus-forming Laboulbeniomycetes in Belgium and the Netherlands is provided. Based on the combined data, we are able to identify mutual gaps that need to be filled as well as weigh the impact of chosen strategies (fieldwork, museum collections) and techniques in these neighboring countries. The aim of this work is to serve as a reference for studying Laboulbeniomycetes fungi in Europe.
... and Uncinula aduncta, rust caused by Melampsora spp., tarry willow spot (willow melanoma) caused by Rhytisma salicinum (Pers.) Fries, stem scab caused by Venturia chlorospora and Physalospora miyabeana, scab of Salix caused by Venturia chlorospora and Venturia saliciperda, and anthracnose of Salix caused by Drepanopeziza sphaerioides and Glomerella miyabeana [10][11][12][13][14][15][16][17][18][19][20][21]. ...
... Fungi of the genus Melampsora cause rust, one of the most important diseases of the willow plant. Melampsora epitea and M. capreum belong to the most common rust species in various geographical regions [10,21]. The above mentioned fungi, through development in leaf tissues and not-related stems, damage the epidermis and the parenchyma, which disturbs the transpiration and assimilation processes of plants and contributes to significant plant weakening and dying [10,14,21,22]. ...
... Melampsora epitea and M. capreum belong to the most common rust species in various geographical regions [10,21]. The above mentioned fungi, through development in leaf tissues and not-related stems, damage the epidermis and the parenchyma, which disturbs the transpiration and assimilation processes of plants and contributes to significant plant weakening and dying [10,14,21,22]. Rusting off of the plant is particularly dangerous for willow species cultivated for energy purposes because defoliation and dying of shoots causes significant economic losses [10,14,21,22]. ...
The species of downy willow ( Salix lapponum ) and swamp willow ( Salix myrtilloides ) are extremely rare relicts among all members of the genus Salix . In Poland, they occur only in the eastern part of the Karkonosze Mountains, Masurian Lake District, and Polesie Lubelskie area. A huge threat to both species is the drainage of peat bogs and their excessive exploitation as well as diseases caused by bacteria and fungi. The present study aimed identify fungal species colonizing the aboveground organs of plants with disease symptoms and to indicate which species may pose a threat towards S. lapponum and S. myrtilloides growing under natural conditions. This research was conducted in Polesie National Park as a part of a research project by the Ministry of Science and Higher Education. Plant health assessments were carried out in natural habitats, while aboveground organs with disease symptoms were collected for laboratory mycological analysis. Colletotrichum salicis (teleomorph Glomerella salicis ), Coniothyrium concentricum , Cylindrosporium salicinum , Phomopsis spp., Truncatella angustata , and Cytospora chrysosperma (teleomorph Valsa sordida ) were the fungal species most frequently isolated from leaves and shoots of both willow species. The above-mentioned fungi are dangerous plant pathogens from the family Salicaceae. There were no obligatory parasites or monophagous pathogens on the aboveground organs of downy or swamp willow. Obligatory parasites may indicate a markedly low population of host plants in Polish conditions.
... The adoption of molecular-based phylogenetic approaches, in lieu of or integrated with morphologic comparisons, over the last two decades has led to the increasing discovery of cryptic rust fungi, indicating that phenotypic similarities can be due to morphological convergence rather than genetic inheritance from a shared ancestor (synapomorphies). Thus, morphological-based classification can be misinformative for inference(s) of evolutionary relationships and delimiting species (Roy et al. 1998;Szabo 2006;van der Merwe et al. 2007;Maier et al. 2003;Hambleton 2010, 2013;Bennett et al. 2011;Yun et al. 2011;Kenaley et al. 2014;Vialle et al. 2013;Hambleton 2010, 2013). This is exemplified by the genus Uromyces, whereby numerous taxa within the genus have long been considered one-celled, teliospore variants of the Puccinia spp. ...
Research was undertaken to clarify the taxonomic identity of leaf rust (Pucciniales) fungi on bioenergy switchgrass in the Eastern and Central U.S. We integrated internal transcribed spacer 2 (ITS2) and partial 28S ribosomal RNA gene sequence data from collections taken from cultivated switchgrass and herbarium specimens, including purported aecial and telial states of Puccinia graminicola and Puccinia pammelii. Maximum likelihood and Bayesian analyses revealed four monophyletic clades: Puccinia emaculata sensu stricto (s.s.), P. pammelii, P. graminicola, and Puccinia novopanici. Results also indicated that P. emaculata s.s. was not affecting cultivated, bioenergy switchgrass. Aecidium pammelii and P. pammelii were distinct phylogenetically from P. emaculata s.s. and grouped within a well-supported clade, demonstrating aecial-telial host alternation for P. pammelii between Euphorbia corollata and switchgrass. Aecidium stillingiae on queen’s delight (Stillingia sylvatica)—a purported aecial state host for P. graminicola—shared identical sequences with the recently described species Puccinia pascua. The latter fungus, however, was recovered within a subclade of P. graminicola. Hence, queen’s delight likely is not an aecial host to P. graminicola s.s. Additional molecular studies are warranted to determine species boundaries within the P. graminicola complex. The majority of contemporary collections from cultivated switchgrass were recognized as P. novopanici. Collectively, bioenergy switchgrass is host to at least three phylogenetically distinct species, presenting a significant challenge to the future selection and breeding of switchgrass with improved rust resistance.
... These relation- ships could vary from latent commensalistic relationship to mutualism or patho- genic infections. In the last 100 years, a number of notable severe forest tree disease outbreaks have been recorded, such as chestnut blight (Milgroom and Cortesi 2004), Dutch elm tree disease (DED) ( Hardwood et al. 2011), root and butt rot diseases ( Asiegbu et al. 2005), poplar rust caused by the biotrophic fungal pathogen Melampsora larici-populina ( Steenackers et al. 1996;Dowkiw and Bastien 2004;Duplessis et al. 2009;Feau et al. 2009;Bennett et al. 2011), and very recently, sudden oak death caused by the oomycete pathogen Phytophthora ramorum ( Gr?nwald et al. 2012). At the other extreme are the mutualistic endophytic microbes, which play important and economically significant roles in plant nutri- tion, nutrient cycling, growth, and health (Sieber 2007;Parent et al. 2009; Mart?n and Nehls 2009; Porras-Alfaro and Bayman 2011). ...
In the natural forest environment, the spread of pathogens may have dramatic effects on ecosystem functioning. To successfully control devastating forest pathogens, application of endophytes as biocontrol agents is an emerging area of research. There are several ways by which endophytic microorganisms can protect their tree hosts against pathogens. Endophytes promote plant growth by producing beneficial secondary metabolites (e.g. phytohormones) or providing nutrients (e.g. phosphorus). Endophytes can compete with pathogens and herbivores by successfully utilizing available substrates (colonization of shared niche can restrict pathogen invasion), or endophytes can produce antagonistic metabolites. Endophytes can enhance plant resistance by triggering and priming host defensive reactions. Endophytes could provide several opportunities for application in integrated pest management (IPM) to gain sustainable forestry practices. To utilize endophytes as biocontrol agents, the mechanisms behind the possible mode of action should be determined. Novel advances in cultivation-independent techniques including next generation sequencing technology (NGS), association analyses and network inference modelling will greatly facilitate identification of endophytes and unravel potential beneficial functions of endophytic communities. A further understanding of these mechanisms could help to minimize the use of environmental harming chemicals in plant and forest tree protection. We propose simple guidelines that could facilitate the use of fungal endophytes as biocontrol agents and simultaneously study their ecological functions.
... The 28S region of rDNA has been used to resolve relationships within and between genera of rust fungi (Aime, 2006;Bennett et al., 2011;Maier et al. 2003Maier et al. , 2007McTaggart et al., 2015), and recovered higher taxonomic relationships within the Pucciniomycotina, alone or in concert with other markers . The results of the present study show that in cases where the 28S region cannot differentiate between species of rust, the ITS2 region may vary between closely related species. ...
Species of Coleosporium (Pucciniales) are rust fungi that typically alternate between pines and angiosperms. In North America, species of Coleosporium often infect Solidago (goldenrods), although their taxonomy on these hosts is unresolved. Joseph. C. Arthur and George B. Cummins regarded these as a single species, Coleosporium solidaginis (fide Arthur) or C. asterum (fide Cummins), but later inoculation studies demonstrated the presence of more than one species, distinguishable by their aecial hosts. A more recent taxonomic study of Coleosporium found that specimens on Solidago identified as C. asterum in North America were not conspecific with the type, which is from Japan, prompting the present study. Herein, we conducted a systematic study on ca. 60 collections of Coleosporium infecting species of Asteraceae from North America using regions of ribosomal DNA and morphology of teliospores and basidia. Our data indicate at least three species of Coleosporium occur on Solidago in North America, C. solidaginis, C. montanum comb. nov., which is proposed for the taxon that has commonly been identified as C. asterum in North America, and C. delicatulum, all of which can be differentiated by morphology of their basidia. In addition, the challenges of marker selection for molecular barcoding of rust fungi is discussed.
