Leveillula buddlejae sp. nov., a new species with an asexual morph resembling phylogenetically basal Phyllactinia species

An asexual morph of a powdery mildew was found on Buddleja asiatica (Scrophulariaceae) in Nepal. The morphological traits of this powdery mildew strongly resemble those of Phyllactinia species (including Ovulariopsis) belonging to a phylogenetically basal group closely related to Leveillula species, but phylogenetic examinations and analyses clearly showed that this fungus pertains to Leveillula. Within the latter genus, it seems to be allied to L. duriaei, but clearly differs from this species in having conidiophores arising from superficial hyphae and narrower conidia with different length/width ratios. Therefore, the powdery mildew on B. asiatica is described as Leveillula buddlejae sp. nov.     

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.     

Loss of Function in Mlo Orthologs Reduces Susceptibility of Pepper and Tomato to Powdery Mildew Disease Caused by Leveillula taurica

Powdery mildew disease caused by Leveillula taurica is a serious fungal threat to greenhouse tomato and pepper production. In contrast to most powdery mildew species which are epiphytic, L. taurica is an endophytic fungus colonizing the mesophyll tissues of the leaf. In barley, Arabidopsis, tomato and pea, the correct functioning of specific homologues of the plant Mlo gene family has been found to be required for pathogenesis of epiphytic powdery mildew fungi. The aim of this study was to investigate the involvement of the Mlo genes in susceptibility to the endophytic fungus L. taurica. In tomato (Solanum lycopersicum), a loss-of-function mutation in the SlMlo1 gene results in resistance to powdery mildew disease caused by Oidium neolycopersici. When the tomato Slmlo1 mutant was inoculated with L. taurica in this study, it proved to be less susceptible compared to the control, S. lycopersicum cv. Moneymaker. Further, overexpression of SlMlo1 in the tomato Slmlo1 mutant enhanced susceptibility to L. taurica. In pepper, the CaMlo2 gene was isolated by applying a homology-based cloning approach. Compared to the previously identified CaMlo1 gene, the CaMlo2 gene is more similar to SlMlo1 as shown by phylogenetic analysis, and the expression of CaMlo2 is up-regulated at an earlier time point upon L. taurica infection. However, results of virus-induced gene silencing suggest that both CaMlo1 and CaMlo2 may be involved in the susceptibility of pepper to L. taurica. The fact that overexpression of CaMlo2 restored the susceptibility of the tomato Slmlo1 mutant to O. neolycopersici and increased its susceptibility to L. taurica confirmed the role of CaMlo2 acting as a susceptibility factor to different powdery mildews, though the role of CaMlo1 as a co-factor for susceptibility cannot be excluded.     

Powdery mildews (Ascomycota,Erysiphales) on Fontanesia phillyreoides and Jasminum fruticans in Turkey

Asexual and sexual morphs of powdery mildews on Fontanesia phillyreoides and Jasminum fruticans, two hitherto unknown host species, have recently been collected in Turkey. Analyses of morphological traits and molecular sequence data led to identifications of the causal agents of the powdery mildew diseases involved. Fontanesia phillyreoides was infected by Phyllactinia fraxini, and the powdery mildew on Jasminum fruticans can be classified as Erysiphe cf. aquilegiae. The latter host showed traces of a co-infection with a second powdery mildew (only asexual morph) belonging to the genus Phyllactinia (= Ovulariopsis) and morphologically well agreeing with P. fraxini.     

Water Stress-Induced Changes in the Morphology of the Powdery Mildew, Leveillula taurica (Lèv.) Arn.

Water stress in Capsiucm annuum L., induced by means of polyethylene glycol influenced the length and branching frequency of conidiophores and conidial dimensions of the powdery mildew, Leveillula taurica (Lèv.) Arn. Conidiophore branching frequency and length as well as conidial length and width decreased with decreasing relative water content. The availability of water to host plants seems to have a direct effect on the growth vigour and development of the powdery mildew possibly is suggested that water stress may be imposed on host plants by the dry harmattan season resulting in reduced growth vigour of the powdery mildew. Morphology of powdery mildew developing under low water potential may be altered.     

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.     

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.     

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.     

First record and characterization of a powdery mildew on a member of the Juncaginaceae: <Emphasis Type="Italic">Leveillula taurica</Emphasis> on <Emphasis Type="Italic">Triglochin maritima</Emphasis>

The powdery mildew fungus Leveillula taurica (Erysiphales) is reported for the first time from the monocot Triglochin maritima (Juncaginaceae), a widespread salt marsh plant that causes economic losses because of its high toxicity to young livestock. This is the first report of an erysiphaceous fungus on a member of the Juncaginaceae. Morphological data, obtained by light and scanning electron microscopy, and ITS sequence data provided evidence that this fungus is referable to L. taurica. The ITS sequence for this fungus was identical with those reported for L. taurica hosted by Capsicum annuum in Australia and Elaeagnus angustifolia in Iran. This is the third host species and second monocot, in addition to Allium cepa and Solanum tuberosum, reported for L. taurica from Washington State, where the fungus was unreported before 2004.     

Erysiphe corylopsidis sp. nov., a new powdery mildew fungus found on Corylopsis spicata and C. pauciflora

A powdery mildew fungus occurring on leaves of Corylopsis pauciflora and C. spicata in Japan is described as a new species, Erysiphe corylopsidis. This species is characterized by fewer than 15 appendages on a chasmothecium, primary branches of the appendages occasionally elongated, and a relatively small number (2–5) of ascospores per ascus. Molecular phylogenetic analyses based on rDNA ITS and 28S rDNA sequences indicate that this fungus forms an independent lineage in the genus Erysiphe.     

Origin and evolution of the powdery mildews (Ascomycota,Erysiphales)

Molecular phylogeny suggests a close relationship of Asteraceae to the early evolution of Golovinomyces. The family Asteraceae, with a geographic origin in South America, expanded into the Northern Hemisphere, where it may have been infected by an ancestor of Golovinomyces, thus starting a close host–parasite relationship. Using this event as a calibration point, we designed molecular clocks for powdery mildews using the 28S rDNA D1/D2 and internal transcribed spacer (ITS) regions. According to these clocks, the powdery mildews originated in the Late Cretaceous and the first radiation of the major lineages occurred at the Cretaceous/Paleogene boundary. Ancestral powdery mildews may have first radiated on broad-leaved deciduous trees in the high latitudes of the Northern Hemisphere, and continued further speciation whilst migrating to southward during the world cooling in the Paleogene and Neogene periods. The cradle of four herb infecting genera, viz. Blumeria, Golovinomyces, Leveillula, and Neoërysiphe may be within the area extending from Central/West Asia to the Mediterranean.     

Molecular cytogenetics of the genus Artemisia (Asteraceae, Anthemideae): fluorochrome banding and fluorescence in situ hybridization. I. Subgenus Seriphidium and related taxa

The distributional pattern of AT- and GC-rich regions and the physical mapping of ribosomal DNA (location of 18S-5.8S-26S and 5S rDNA) in the chromosomes of seven Artemisia species have been established by means of fluorochrome banding and fluorescence in situ hybridization (FISH). This is the first study in the large genus Artemisia using FISH. Five species (A. barrelieri, A. caerulescens subsp. gallica, A. fragrans, A. herba-alba subsp. valentina, A. herba-alba subsp. herba-alba) belong to the subgenus Seriphidium, one of the most homogeneous in the genus; one (A. tridentata susbp. spiciformis) belongs to the small subgenus Tridentatae, classically included in Seriphidium; and one (A. annua) belongs to the subgenus Artemisia, but shows some affinities with Seriphidium. Genome organization is relatively constant in all the species studied. AT- and GC-rich DNA is predominantly terminal, but some intercalary and centromeric bands also exist. The rDNA loci are also most often terminal and usually located in GC-rich regions. 5S rDNA sites are present in a lower number than 18S-5.8S-26S sites, and are always colocated with some of them. In the light of these cytogenetic features, subgenus Seriphidium is clearly placed within the genus Artemisia, so that it does not make sense to segregate it as a genus; on the other hand, subgenus Tridentatae must not be classified within Seriphidium, but kept as an independent subgenus.     

Species delimitation in downy mildews: the case of Hyaloperonospora in the light of nuclear ribosomal ITS and LSU sequences

Species definitions for plant pathogens have considerable practical impact for measures such as plant protection or biological control, and are also important for comparative studies involving model organisms. However, in many groups, the delimitation of species is a notoriously difficult taxonomic problem. This is particularly evident in the obligate biotrophic downy mildew genera (Peronosporaceae, Peronosporales, Oomycetes), which display a considerable diversity with respect to genetic distances and host plants, but are, for the most part, morphologically rather uniform. The recently established genus Hyaloperonospora is of particular biological interest because it shows an impressive radiation on virtually a single host family, Brassicaceae, and it contains the downy mildew parasite, Arabidopsis thaliana, of importance as a model organism. Based on the most comprehensive molecular sampling of specimens from a downy mildew genus to date, including various collections from different host species and geographic locations, we investigate the phylogenetic relationships of Hyaloperonospora by molecular analysis of the nuclear ribosomal ITS and LSU sequences. Phylogenetic trees were inferred with ML and MP from the combined dataset; partitioned Bremer support (PBrS) was used to assess potential conflict between data partitions. As in other downy mildew groups, the molecular data clearly corroborate earlier results that supported the use of narrow species delimitations and host ranges as taxonomic markers. With few exceptions, suggested species boundaries are supported without conflict between different data partitions. The results indicate that a combination of molecular and host features is a reliable means to discriminate downy mildew species for which morphological differences are unknown.     

Inoculum production and long-term conservation methods for cucurbits and tomato powdery mildews

The behaviour of cucurbit powdery mildews (Podosphaera xanthii and Golovinomyces cichoracearum) and tomato powdery mildew (Oidium neolycopersici) infesting detached cotyledons of Lagenaria leucantha cv. ‘Minibottle’ was studied in order to develop an easy culture method for pure inoculum production. High spore production was found with a combination of mannitol (0.1 m), sucrose (0.02 m) and agar (8 g l⁻¹) in the cotyledon survival medium. Sporulation on cotyledons and viability of conidia were affected by the age of culture for the three species of powdery mildew tested. The age of cotyledons had also an impact of the spore production. This method was used to produce large amounts of inoculum for P. xanthii, G. cichoracearum and O. neolycopersici and enable the development of other species of powdery mildew like Leveillula taurica. Freezing conidia in liquid nitrogen enabled the long-term conservation of P. xanthii without any loss of virulence. The same method was unsuccessful with G. cichoracearum, and L. taurica and partly successful with O. neolycopersici.     

Molecular mapping of a recessive powdery mildew resistance gene in spelt wheat cultivar Hubel

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most important wheat diseases worldwide. The basis for wheat powdery mildew resistance breeding consists of screening diversified host genetic resources with a range of races of the powdery mildew pathogen. Spelt wheat (Triticum aestivum ssp. spelta 2n = 6x = 42, AABBDD) is a close relative of common wheat (T. aestivum ssp. aestivum) and contains several known disease resistance genes, including Pm1d, Yr5, and Lr65. Here, we report the identification and mapping of a powdery mildew resistance gene in spelt wheat cultivar Hubel, which was introduced to China from Europe and is resistant to Chinese Bgt isolate E09 at the seedling stage. Genetic analysis of a recombinant inbred line population derived from a cross of Hubel and a susceptible early maturing mutant line indicated that Hubel possessed a recessive powdery mildew resistance gene (temporarily designated MlHubel). Markers linked to MlHubel were identified using bulked segregant analysis, simple sequence repeat, and expressed sequence tag-derived sequence tagged site methods. The linked markers were physically located on wheat chromosome 2D. Comparative genomic analysis indicated that the genetic interval covering MlHubel in wheat is highly colinear with the corresponding regions on Brachypodium distachyon chromosome 5 and Oryza sativa chromosome 4. Accordingly, the genetic map of MlHubel was established in comparison with B. distachyon 5L and O. sativa 4L, with the closest marker Xgwm265 being 0.4 cM from MlHubel. The identification of the recessive powdery mildew gene in spelt wheat suggests the potential of this accession along with its closely linked markers in breeding for resistance to powdery mildew.     

Potential of Lecanicillium spp. for management of insects, nematodes and plant diseases

Fungi in the genus Lecanicillium (formerly classified as the single species Verticillium lecanii) are important pathogens of insects and some have been developed as commercial biopesticides. Some isolates are also active against phytoparasitic nematodes or fungi. Lecanicillium spp. use both mechanical forces and hydrolytic enzymes to directly penetrate the insect integument and the cell wall of the fungal plant pathogen. In addition to mycoparasitism of the plant pathogen, the mode of action is linked to colonization of host plant tissues, triggering an induced systemic resistance. Recently it was demonstrated that development of Lecanicillium hybrids through protoplast fusion may result in strains that inherit parental attributes, thereby allowing development of hybrid strains with broader host range and other increased benefits, such as increased viability. Such hybrids have demonstrated increased virulence against aphids, whiteflies and the soybean cyst nematode. Three naturally occurring species of Lecanicillium, L. attenuatum, L. longisporum, and an isolate that could not be linked to any presently described species based on rDNA sequences have been shown to have potential to control aphids as well as suppress the growth and spore production of Sphaerotheca fuliginea, the causal agent of cucumber powdery mildew. These results suggest that strains of Lecanicillium spp. may have potential for development as a single microbial control agent effective against several plant diseases, pest insects and plant parasitic nematodes due to its antagonistic, parasitic and disease resistance inducing characteristics. However, to our knowledge, no Lecanicillium spp. have been developed for control of phytopathogens or phytoparasitic nematodes.     

Intraspecies differentiation in the powdery mildew Erysiphe cichoracearum determined with rDNA RFLPs

The powdery mildew species Erysiphe cichoracearum has a described host range of over 300 plant species from among several families. Host-range testing indicates host-specialized subdivision within this taxonomic species. However, the extent of subdivision remains largely undetermined among host-limited forms. We have characterized diversity among field collections of E. cichoracearum from a variety of hosts, and from other powdery mildew species, with RFLPs from a PCR amplified ribosomal DNA (rDNA) segment The E. cichoracearum samples expressed six distinct RFLP haplotypes. Each haplotype was specific to either a single host or to a set of related host species. These haplotypes formed a continuum of divergence ranging from about 18–35% average pairwise distance from one another, while those from other mildew species clustered at consistently higher average pairwise distances from E. cichoracearum and from each other. Our findings support earlier suggestions, based on host-range and morphological characterizations, that E. cichoracearum is a complex of morphologically similar, but host-limited forms. Also, comparisons of rDNA haplotype distance between E. cichoracearum and Blumeria (Erysiphe) graminis were consistently greater than between E. cichoracearum and Sphaerotheca fulginea. This result supports earlier questions concerning the monophyletic nature of Erysiphe.     

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.