Molecular phylogenetic analyses reveal a close relationship between powdery mildew fungi on some tropical trees and Erysiphe alphitoides, an oak powdery mildew

To investigate the phylogenetic relationships among the powdery mildew fungi of some economically important tropical trees belonging to Oidium subgenus Pseudoidium, we conducted molecular phylogenetic analyses using 30 DNA sequences of the rDNA internal transcribed spacer (ITS) regions and 26 sequences of the domains D1 and D2 of the 28S rDNA obtained from the powdery mildews on Hevea brasiliensis (para rubber tree), Anacardium occidentale (cashew), Bixa orellana, Citrus spp., Mangifera indica (mango), and Acacia spp. The results indicate that the powdery mildew fungi isolated from these tropical trees are closely related to one another. These powdery mildews are also closely related to E. alphitoides (including Erysiphe sp. on Quercus phillyraeoides). Because of the obligate biotrophic nature of the powdery mildew fungi, the relationship between powdery mildews and their host plants is conservative. However, the present study suggests that a particular powdery mildew species has expanded its host ranges on a wide range of the tropical trees. This article also suggests that a powdery mildew fungus distributed in temperate regions of the Northern Hemisphere expanded its host ranges onto tropical plants and may be a good example of how geographical and host range expansion has occurred in the Erysiphales.     

Phylogeny and taxonomy of the oak powdery mildew Erysiphe alphitoides sensu lato

Phylogenetic analyses of Erysiphe alphitoides s. lat. using sequences of the rDNA ITS region and the D1/D2 domains of the 28S rDNA revealed a complex consisting of several genetically and morphologically distinguished taxa, including the already described Erysiphe alphitoides s. str. and E. hypophylla. The ascomata (chasmothecia) of E. hypophylla are morphologically very similar to those of E. alphitoides, but the two species are easily distinguishable by their symptoms, as well as the shape and size of the conidia. The fungus on Quercus phillyraeoides, distributed in warmer regions in southern Japan, is genetically clearly separated from E. alphitoides s. str., and morphologically characterized by having chasmothecia with appendages consistently shorter than the chasmothecial diameter. This fungus, named Erysiphe quercicola in this paper, is also able to infect some other oak species, and it is genetically identical with anamorphs on some tropical trees of other host genera. Collections of E. alphitoides s. lat. on Quercus acutissima and Q. variabilis, both belonging to Quercus sect. Cerris, are genetically distinct from E. alphitoides s. str., E. hypophylla and E. quercicola. They form two genetically and morphologically differentiated groups. The hypophyllous taxon on Q. acutissima and Q. variabilis, named Erysiphe hypogena in this paper, is characterized by forming distinctive persistent hypophyllous mycelial patches, causing necrotic discolouration of the host tissue. The epiphyllous taxon on these hosts, for which the name E. epigena is proposed, differs in having epiphyllous mycelium, smaller chasmothecia with fewer appendages, and does not cause leaf discolouration.     

Molecular phylogenetic and morphological analyses of Oidium heveae, a powdery mildew of rubber tree

Powdery mildew of rubber tree caused by Oidium heveae is an important disease of rubber plantations worldwide. Identification and classification of this fungus is still uncertain because there is no authoritative report of its morphology and no record of its teleomorphic stage. In this study, we compared five specimens of the rubber powdery mildew fungus collected in Malaysia, Thailand, and Brazil based on morphological and molecular characteristics. Morphological results showed that the fungus on rubber tree belongs to Oidium subgen. Pseudoidium. Nucleotide sequence analysis of the ribosomal DNA internal transcribed spacer (ITS) region and the large subunit rRNA gene (28S rDNA) were conducted to determine the relationships of the rubber powdery mildew fungus and to link this anamorphic fungus with its allied teleomorph. The results showed that the rDNA sequences of the two specimens from Malaysia were identical to a specimen from Thailand, whereas they differed by three bases from the two Brazilian isolates: one nucleotide position in the ITS2 and two positions in the 28S sequences. The ITS sequences of the two Brazilian isolates were identical to sequences of Erysiphe sp. on Quercus phillyraeoides collected in Japan, although the 28S sequences differed at one base from sequences of this fungus. Phylogenetic trees of both rDNA regions constructed by the distance and parsimony methods showed that the rubber powdery mildew fungus grouped with Erysiphe sp. on Q. phillyraeoides with 100% bootstrap support. Comparisons of the anamorph of two isolates of Erysiphe sp. from Q. phillyraeoides with the rubber mildew did not reveal any obvious differences between the two powdery mildew taxa, which suggests that O. heveae may be an anamorph of Erysiphe sp. on Q. phillyraeoides. Cross-inoculation tests are required to substantiate this conclusion.     

<Emphasis Type="Italic">Erysiphe monascogera</Emphasis> sp. nov., an unusual powdery mildew fungus found on fruits of <Emphasis Type="Italic">Styrax japonica</Emphasis>

Morphological observations using light and scanning electron microscopes and molecular phylogenetic analysis revealed that the fungus growing on the surface of fruits or sepals of Styrax japonica collected at Nagano, Japan, is a new powdery mildew with an unusual morphology, described here as Erysiphe monascogera. This fungus has mainly a single ascus in a chasmothecium, but molecular phylogenetic analysis and the shape of the hyphal appressoria suggest that it is an Erysiphe species. Erysiphe monascogera is a sister-species to E. nomurae on Symplocos chinensis var. leucocarpa f. pilosa, although there are obvious morphological differences between the two species. This inconsistency between molecular phylogeny and morphology may be explained by the unique habitat of E. monascogera. Erysiphe monascogera and E. nomurae are included in a clade composed of the E. alphitoides complex, which suggests that these two species diverged by host jumping of the E. alphitoides complex, having oaks as major host plants.     

Interspecific and intraspecific diversity in oak powdery mildews in Europe: coevolution history and adaptation to their hosts

Quercus has been reported as the genus with the largest number of attacking powdery mildews. In Europe, oak powdery mildew was rarely reported before 1907, when severe outbreaks were observed. These epidemics were attributed to the newly described species Erysiphe alphitoides, presumed to be of exotic origin. After the burst of interest following the emergence of the disease, research on this topic remained very limited. Interest in research was recently reactivated in response to the availability of molecular tools. This review summarizes current knowledge on the diversity of oak powdery mildews in Europe and their possible evolutionary relationships with European oaks. The most striking results are the evidence of cryptic diversity (detection in France of a lineage closely related to Erysiphe quercicola, previously thought to only have an Asian distribution), large host range (similarity of E. alphitoides and E. quercicola with powdery mildews of tropical plants) but also local adaptation to Quercus robur. These recent findings highlight the complexity of the history of oak powdery mildew in Europe and point to the question of host specialization and host jumps in the evolution of powdery mildew fungi.     

Sawadaea nankinensis comb. nov.: a powdery mildew fungus of Acer buergerianum

The anamorphic state of a powdery mildew on trident maple (Acer buergerianum, Aceraceae), belonging to Sawadaea, has been observed since 1980 in Tokyo and other areas of Japan. Since the autumn of 2003, this fungus has begun to produce chasmothecia in various areas of Japan, which were consistent with Erysiphe nankinensis (= Uncinula nankinensis), but apparently contradictory to the characteristics of the anamorph. Based on a molecular phylogenetic analysis using DNA separately extracted from the anamorph and teleomorph of the fungus on A. buergerianum, it could be demonstrated that sequences of this fungus are sister to Sawadaea. As the anamorph belongs to Oidium subgen. Octagoidium and because of the phylogenetic position within the Sawadaea clade, the new combination Sawadaea nankinensis is proposed for this species. The genus Sawadaea is emended to comprise species with consistently unbranched appendages.     

Phylogeny and taxonomy of powdery mildew fungi of Erysiphe sect. Uncinula on Carpinus species

A phylogenetic analysis of the Erysiphe with uncinuloid ascoma appendages (Erysiphe section Uncinula, Erysiphales, Ascomycota) on Carpinus spp. was done using sequences of the rDNA ITS regions and the D1/D2 domains of the 28S rDNA. These results, combined with morphological data, revealed a complex consisting of several distinct taxa. These included the already described Erysiphe carpinicola on C. japonica distinguishable from the Erysiphe sp. on C. betulus and C. tschonoskii as well as the one on C. laxiflora. Thus, it was shown that Oidium carpini, described from Europe on Carpinus betulus, the powdery mildew with uncinula-like ascomata, recently found in Europe on this host, as well as an Erysiphe on C. tschonoskii in Japan, described previously as E. carpinicola, all belong to a single new species, named E. arcuata in this paper. As the powdery mildew on C. laxiflora was also distinct from other known species, it is named E. carpini-laxiflorae in this paper. The already described E. pseudocarpinicola and Erysiphe sp. on Carpinus cordata are two additional taxa, which are morphologically and genetically distinguished from the other species of Erysiphe sect. Uncinula on Carpinus spp.     

Two Erysiphe species associated with recent outbreak of soybean powdery mildew: results of molecular phylogenetic analysis based on nuclear rDNA sequences

 Serious outbreaks of powdery mildew by a fungus belonging to the mitosporic genus Oidium subgenus Pseudoidium have been reported on soybean (Glycine max) in a wide area of eastern Asia since 1998. The taxonomic and phylogenetic placement of the causal fungus has not yet been determined because of lack of the perfect stage. We found ascomata having mycelioid appendages on a single leaf of soybean infested by powdery mildew. Molecular phylogenetic analysis was conducted based on a total of 14 sequences of the rDNA internal transcribed spacer (ITS) region from 13 soybean and wild soybean (Glycine soja) materials collected in Japan, Korea, Vietnam, and the United States, combined with 47 sequence data obtained from the DNA databases. It was revealed that two Erysiphe species were associated with the outbreak of soybean powdery mildew. There was 16% difference between the two species in genetic divergence of the ITS sequence. One species with perfect stage has an ITS sequence identical to that of Erysiphe glycines on Amphicarpaea and is identified as Erysiphe glycines based on the ITS sequence and morphology of ascomata. The second species, without the perfect stage, is likely to be Erysiphe diffusa (= Microsphaera diffusa), known as the fungus causing soybean powdery mildew in the United States, because the ITS sequences are identical to those from materials collected in the United States. However, we need materials having ascomata of E. diffusa to confirm the species name. Received: March 15, 2002 / Accepted: May 22, 2002     

Two new hosts of anamorphic Erysiphe quercicola: Cinnamomum camphora and Murraya paniculata

Based on collections of powdery mildews (Erysiphales) in Taiwan and combined molecular and morphological analyses, camphor tree (Cinnamomum camphora) and orange jasmine (Murraya paniculata) are recognized as new hosts of the anamorph of the powdery mildew Erysiphe quercicola. The anamorphic powdery mildew on C. camphora has been known as Pseudoidium cinnamomi, but its relationship to a teleomorph was unknown. For M. paniculata as substrate of powdery mildew, only an anamorphic Cystotheca species has been named. Morphological investigation of the fungus on this host shows that the specimens from Taiwan belong to another genus because of the lack of fibrosin bodies. Analysis of internal transcribed spacer sequences indicates that the anamorphic powdery mildews on camphor and orange jasmine belong to a clade representing E. quercicola, with the teleomorph found only on oak species (Quercus, Fagaceae), but with its anamorph reported from a broad host range, particularly in the tropics.     

Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) as a potential mycoparasite on Sphaerotheca fuliginea (Ascomycotina: Erysiphales)

Hyphomycete Paecilomyces fumosoroseus that is well known as saprophytic and entomopatogenic fungus was investigated for its mycoparasitism on the cucumber powdery mildew pathogen. Mycoparasitism was documented by using standard bioassay and SEM. Effects of mycoparasitism were evaluated in three types of experiments. Paecilomyces fumosoroseus was applied in the form of graded suspensions into a colony of powdery mildew on a leaf segment. Interaction between both fungi was observed as the percentage of colonized area vs. experimental time. In the second experiment, young cucumber plants were sprayed with a suspension of Paecilomyces fumosoroseus 24 h before inoculation of Sphaerotheca fuliginea. Pre-treatment with P. fumosoroseus reduced development and spreading of powdery mildew infection significantly 15 days post-inoculation in contrast to pre-treatments with sulfur fungicide and distilled water. The development of pure culture powdery mildew under determined experimental conditions was observed and compared with treated variants. In the third experiment, mildewed plants were treated with a suspension of P. fumosoroseus. The control treatments with sulfur fungicide and distilled water were tested. Effects of P. fumosoroseus on the dispersion of powdery mildew during a 21-day period were observed.P. fumosoroseus suppressed the development and spread of cucumber powdery mildew significantly during the time of the experiment. The mechanical and physical damages and disruptions of vegetative and fruiting structures of powdery mildew were recorded under light microscopy and S.E.M.Results were concluded in pursuance to differences between the natural behaviour and development of S. fuliginea on cucumber plants treated with P. fumosoroseus and non-treated plants.     

Powdery Mildew Caused by an Erysiphe sp. on Korean Ginseng

In August and September 2014, Korean ginseng (Panax ginseng) plants showing symptoms of powdery mildew infection were found in a polyethylene film‐covered greenhouse in Suwon, Korea. The mildew was initially observed to occur in circular to irregular white colonies, which subsequently developed into abundant mycelial growths on both leaf surfaces. No chasmothecia were observed. Based on its morphological characteristics, the fungus was determined to be a species of Erysiphe. Phylogenetic analysis of the sequence of the internal transcribed spacer region of the ribosomal DNA obtained from the isolate placed the powdery mildew fungus in the genus Erysiphe. Here, we describe this Erysiphe sp. found growing on Korean ginseng using both illustrations and molecular data. A comparison of the Korean isolate and three previous records of powdery mildews known to grow on Panax plants is also provided. This is the first report of powdery mildew on Korean ginseng in Korea.     

A new subgenus, Microidium, of Oidium (Erysiphaceae) on Phyllanthus spp.

Powdery mildew fungi found on leaves, shoots, and stems of Phyllanthus acidus, P. amarus, and P. reticulatus proved to be a fungus having morphology unique in the Erysiphaceae. Light micrographs of a new germination pattern are added to discuss differences to other four germination patterns of the powdery mildews. The rDNA sequences (28S and 18S regions) of the fungi found on Phyllanthus spp. form a distinct monophyletic clade strongly supported by bootstrap (100%) in 18S + 28S trees, which indicates that the fungus is an isolated fungal group among the Erysiphaceae in tribal level. Because we cannot find the teleomorphic state of this fungus, a new subgenus Microidium of anamorphic genus Oidium is proposed to accommodate this organism.     

Re-consideration of Peronospora farinosa infecting Spinacia oleracea as distinct species, Peronospora effusa

Downy mildew is probably the most widespread and potentially destructive global disease of spinach (Spinacia oleracea). The causal agent of downy mildew disease on various plants of Chenopodiaceae, including spinach, is regarded as a single species, Peronospora farinosa. In the present study, the ITS rDNA sequence and morphological data demonstrated that P. farinosa from S. oleracea is distinct from downy mildew of other chenopodiaceous hosts. Fifty-eight spinach specimens were collected or loaned from 17 countries of Asia, Europe, Oceania, North and South America, which all formed a distinct monophyletic group. No intercontinental genetic variation of the ITS rDNA within Peronospora accessions causing spinach downy mildew disease was found. Phylogenetic trees supported recognition of Peronospora from spinach as a separate species. Microscopic examination also revealed morphological differences between Peronospora specimens from Spinacia and P. farinosa s. lat. specimens from Atriplex, Bassia, Beta, and Chenopodium. Consequently, the name Peronospora effusa should be reinstated for the downy mildew fungus found on spinach. Here, a specimen of the original collections of Peronospora effusa is designated as lectotype.     

Erysiphe kenjiana (Erysiphales), a new invasive fungus in Europe

An Asian powdery mildew fungus Erysiphe (Uncinula) kenjiana (Erysiphales, Ascomycota) has been found in Ukraine. This is the first record of this fungus in Europe. In 2007, E. kenjiana was collected on four Ulmus species in Kiev. All locations adjoined railways or an airport. Development of E. kenjiana was epiphytotic. This species was not found on elms surveyed at towns situated north-east, east or south of Kiev. The fungus may have been brought directly to Ukraine by rail or air transport. In 2008, the fungus was also collected in Chernihiv situated north-east of Kiev. It is likely that E. kenjiana will spread over all Ukraine and into countries of central and western Europe in 2009 or later. Molecular phylogenetic analyses using D1/D2 domains of the 28S rDNA and ITS sequences revealed that the Ulmaceae-Cannabaceae-parasitic powdery mildews, including E. kenjiana, form a clade with strong supports, suggesting that these species diverged from a single ancestor and expanded their host ranges within the Ulmaceae and allied Cannabaceae. This hypothesis is supported by these species sharing the unique morphology of enlarged apices on their chasmothecial appendages. These fungi formed part of a larger grouping with species on Fagaceae, Nothofagaceae, Rosaceae, and Sapindaceae with strong statistical supports. These results suggest that Uncinula-like powdery mildew fungi on these plant families exhibit close evolutionary relationships with their hosts.     

Ascospore formation and morphology in two species of the genusErysiphe remaining immature on the living host plant

Erysiphe cumminsiana andE. galeopsidis, which have immature asci in the current season, have been recorded from Japan, but the ascospores of both fungi have not been described. In the present experiments, some observations before and after overwintering were made on the cleistothecia ofE. cumminsiana on three species ofCacalia and two species ofLigularia, andE. galeopsidis onGeranium thunbergii. After overwintering, the former fungus developed six to eight, rarely four spores in an ascus and the latter fungus always four spores in an ascus. Their teleomorphic characteristics including those of ascospores are also described.     

A new species of <Emphasis Type="Italic">Brasiliomyces</Emphasis> (Erysiphaceae) on <Emphasis Type="Italic">Dalbergia cultrata</Emphasis> var. <Emphasis Type="Italic">cultrata</Emphasis> from Thailand

A powdery mildew fungus on leaves of Dalbergia cultrata var. cultrata (Fabaceae) collected at the Queen Sirikit Botanical Garden in northern Thailand is proven to be a new species of the genus Brasiliomyces and is described as B. chiangmaiensis sp. nov. with light and SEM micrographs. Differences in known Brasiliomyces species are discussed, and a key to species of this genus is provided.     

Molecular and morphological characterization of Leveillula (Ascomycota: Erysiphales) on monocotyledonous plants

Leveillula on monocotyledonous plants have been recorded as L. taurica by several authors, whereas the fungus on Allium has been described as an independent species, namely L. allii, by some authors. We sequenced ca 600 bp of the rDNA ITS region for two Leveillula specimens from Allium and Polianthes (both from monocotyledons) and compared them with several already published sequences from Leveillula isolates from dicotyledons. Pair-wise percentages of sequence divergences were calculated for all Leveillula isolates. The ITS sequence of the Polianthes isolate was identical to L. taurica on Helianthus and Vicia. The sequence of the Allium isolate was 99.5 % identical to L. taurica on Euphorbia, Haplophylum, Peganum, etc. These results suggest close relationships between monocot and dicot pathogenic Leveillula species. The identity between two monocot isolates was 98.4 %. Phylogenetic analysis revealed that the two monocot isolates do not group into a clade together. This result suggests that Leveillula acquired parasitism to monocots at least twice independently.     

Molecular marker analyses of powdery mildew resistance in barley

Powdery mildew, caused byEryisphe graminis f. sp.hordei, is one of the most important diseases of barley (Hordeum vulgare). A number of loci conditioning resistance to this disease have been reported previously. The objective of this study was to use molecular markers to identify chromosomal regions containing genes for powdery mildew resistance and to estimate the resistance effect of each locus. A set of 28 F₁ hybrids and eight parental lines from a barley diallel study was inoculated with each of five isolates ofE. graminis. The parents were surveyed for restriction fragment length polymorphisms (RFLPs) at 84 marker loci that cover about 1100 cM of the barley genome. The RFLP genotypes of the F₁s were deduced from those of the parents. A total of 27 loci, distributed on six of the seven barley chromosomes, detected significant resistance effects to at least one of the five isolates. Almost all the chromosomal regions previously reported to carry genes for powdery mildew resistance were detected, plus the possible existence of 1 additional locus on chromosome 7. The analysis indicated that additive genetic effects are the most important component in conditioning powdery mildew resistance. However, there is also a considerable amount of dominance effects at most loci, and even overdominance is likely to be present at a number of loci. These results suggest that quantitative differences are likely to exist among alleles even at loci which are considered to carry major genes for resistance, and minor effects may be prevalent in cultivars that are not known to carry major genes for resistance.