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.     

Identity of a powdery mildew fungus occurring on Paeonia and its relationship with Erysiphe hypophylla on oak

A powdery mildew fungus found on Paeonia lutea at the Botanical Garden of Geneva (Switzerland) was identified as Erysiphe hypophylla based on morphological observations. The occurrence of E. hypophylla on Paeonia seemed curious, because host plants of this species have been restricted to a few Quercus species of the family Fagaceae. In this study, we determined the rDNA sequences of the powdery mildew specimens on Paeonia and E. hypophylla on Quercus to confirm the identity of the Paeonia fungus. The three sequences from the specimens on P. lutea were identical to one another in both ITS and 28S rDNA regions and also to the sequences of E. hypophylla on Q. robur, which supports the identification that the fungus on P. lutea is E. hypophylla. However, these sequences were also identical to the sequences of E. alphitoides on Quercus spp. and Oidium mangiferae on mango. This result suggests a possibility that E. hypophylla is conspecific to E. alphitoides. Further study is required to clarify whether E. hypophylla is a synonym of E. alphitoides or a distinct species.     

<Emphasis Type="Italic">Erysiphe fimbriata</Emphasis> sp. nov.: a powdery mildew fungus found on <Emphasis Type="Italic">Carpinus laxiflora</Emphasis>

Ascomata of a powdery mildew-like fungus have been found on Carpinus laxiflora in Tochigi Prefecture of Japan since 2003. The morphological and molecular characteristics of this fungus are reported, and a new species, Erysiphe fimbriata, is proposed. It has large chasmothecia (200–250 μm in diameter) with long (up to 4–5 mm in length), fimbriate appendages arising from the upper half of the chasmothecia and turning upward, and numerous asci (22–38 per chasmothecium). Erysiphe fimbriata is a unique fungus both genetically and morphologically.     

<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.     

New records of microcyclic conidiogenesis in some powdery mildew fungi

Microcyclic conidiogenesis (MC) was recently described in several species of powdery mildew fungi. This process, defined as the production of conidia on a fungal spore without any, or only a minimal, involvement of hyphal growth, was observed on powdery mildew conidia that have already germinated on host plant surfaces and have been attached to the epidermal cells. Most probably, MC contributes to a quick propagation of young powdery mildew colonies because new conidia are sometimes produced in a shorter time on microcyclic conidiophores than on the hyphae of the young mycelium. This article reports MC in Erysiphe necator ex grapevine, Podosphaera leucotricha ex apple, Golovinomyces orontii ex tobacco, and Neoerysiphe galeopsidis ex Lamium purpureum based on light and low-temperature scanning electron microscopic studies.     

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.     

Biochemical genetics of powdery mildew resistance in pea

Summary A biochemical study on phenolic (total phenols and orthodihydroxy phenols) content and on the activities of phenol oxidizing enzymes (peroxidase and polyphenol oxidase) in pea cultivars resistant and susceptible to powdery mildew infection revealed that the resistant cultivars contained higher levels of phenolics and phenol-oxidizing enzymes than the susceptible ones. A further study of their F₁s, F₂s and backcross progenies suggested a high heritability for all biochemical traits. The correlation coefficients between the biochemical parameters and the disease index were also high. Both additive (d) and dominant () components were found to contribute to the inheritance of these constituents.Associate Professor (Genetics), Department of Basic Sciences     

Patterns of post-infectional protein synthesis in barley carrying different genes for resistance to the powdery mildew fungus

Summary Pairs of susceptible and resistant, near-isogenic cultivars ofHordeum vulgare which differ for the Mla, Mlk and Mlp genes for resistance toErysiphe graminis f. sp.hordei were inoculated with race 3 of this pathogen and patterns of protein synthesis associated with primary infection mapped using pulse-labelling with L-[³⁵S]methionine and 2-dimensional electrophoresis. Extraction of proteins with buffer containing detergent revealed the enhanced synthesis of 5 and 8 polypeptides at 25 and 30 h respectively after inoculation of barley carrying the Mla gene (cvMla). The enhanced synthesis of these same polypeptides together with 11 additional polypeptides was observed at 48 h and 72 h after inoculation of barley carrying either the Mlp (cvMlp) or Mlk (cvMlk) genes. The labelling of several major constitutive polypeptides was suppressed in cvMla at 24 h after inoculation; the labelling of six of these polypeptides was also suppressed in both cvMlp and cvMlk but not until 48 and 72 h after inoculation. These results indicate that changes occur in the synthesis of some common polypeptides following infection of cultivars carrying different resistance genes but the timing and extent of these changes varies with the resistance gene in the host.     

Seedling resistance of wheat to the powdery mildew fungus,Erysiphe graminis f. sp. tritici. I. Resistance of first leaves

During primary infection by conidia ofErysiphe graminis f. sp.tritici, three mechanisms of resistance operate in first leaves of 8-day-old seedlings of both resistant and susceptible wheats. The first mechanism, operating at the penetration site, is responsible for the failure of penetrations attempted by primary germ tubes (PGT). The second mechanism is concerned with the abortion of haustoria in normal-appearing host cells. The third mechanism relates to the abortion of haustoria and the hypersensitivity of the penetrated host cells.With the inoculum-level of 19–24 conidia/mm², the three mechanisms together prevented 89.3 % of the attempted penetrations by PGT from producing normal haustoria in resistant wheat Purdue 5752C1-7-5-1 and 37.4 % in the susceptible wheat Vermillion. The first mechanism accounted for the prevention of 73.3 % of the attempted PGT penetrations on Purdue 5752C1-7-5-1 and 36 % on Vermillion. The second mechanism was responsible for stopping 19 % of all the successful penetrations in Purdue 5752C1-7-5-1 and 0.8 % in Vermillion. The third mechanism accounted for the failure of 41 % of all the successful penetrations in Purdue 5752C1-7-5-1 and 1.4% in Vermillion. Thirty-six hours after inoculation, 10.7% of all the attempted PGT penetrations appeared to be developing normally in first leaves of 8-day-old seedlings of resistant wheat Purdue 5752C1-7-5-1 as compared to 62.6 % in the susceptible wheat Vermillion.This appears to be the first report showing the relative effectiveness of various mechanisms of resistance concerning any powdery mildew fungus.     

Genetic analysis of the obligate parasitic barley powdery mildew fungus based on RFLP and virulence loci

Summary Genome organization of the biotrophic barley powdery mildew fungus was studied using restriction fragment length polymorphism (RFLP). Genomic DNA clones containing either low-or multiple-copy sequences appeared to be the best RFLP markers, as they frequently revealed polymorphisms that could be readily detected. A total of 31 loci were identified using 11 genomic DNA clones as probes. Linkage analysis of the 31 RFLP loci and five virulence loci resulted in the construction of seven groups of linked loci. Two of these contained both RFLP markers and virulence genes. RFLP markers were found to be very efficient in characterizing mildew isolates, as only three markers were necessary to differentiate 28 isolates. The DNA of the barley powdery mildew fungus appeared to contain a considerable number of repetitive sequences dispersed throughout the genome.     

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.     

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 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.     

Inheritance of partial resistance to powdery mildew in spring wheat

Summary Four spring wheat (Triticum aestivum L.) cultivars exhibiting partial resistance to powdery mildew induced by Erysiphe graminis f.sp. tritici were crossed to a common susceptible cultivar to study the inheritance of resistance. The genetic parameters contributing to resistance were estimated by generation means analyses. Additive gene action was the most important genetic component of variation among generation means in all four crosses. Additive by additive effects were significant in one cross and both additive by additive and additive by dominance effects were significant in another. Dominance effects were not significant. The F2/F3 correlations in three crosses ranged from 0.27 to 0.43. Three additional crosses among resistant cultivars were employed to study the effectiveness of selection in improving resistance. By selecting the most resistant plants from the F2 and evaluating the progenies in the F4, increases in resistance ranging from 21% to 31% were obtained. In all crosses, there was transgressive segregation in both directions indicating that the genes conferring resistance to these cultivars differ and exhibit additive effects.     

PCR primers useful for nucleotide sequencing of rDNA of the powdery mildew fungi

Four PCR primers that are useful to determine the nucleotide sequences of the rDNA of the powdery mildew fungi were newly designed. These primers provide both enough stability to work on a wide range of powdery mildews and enough specificity to eliminate contaminating DNA by PCR. DNA sequences of the rDNA ITS region were successfully obtained from specimens that were contaminated by other fungi. In addition, sequence results of the 18S and 28S rDNA were dramatically improved by using these primers in most of the specimens examined.     

Inheritance of powdery mildew (Erysiphe polygoni DC) resistance in mungbean (Vigna radiata L. Wilczek)

Detached mungbean (Vigna radiata L.Wilczek) leaves were inoculated with a conidial suspension of a local isolate (TI-1) of the powdery mildew pathogen (Erysiphe polygoni DC) under controlled environment conditions. Based on the latent period and severity of the infection, a rating scale of 0–5 was used to classify the host pathogen interactions. Reactions 0, 1 and 2 were considered resistant and referred to as R0, R1 and R2 while 3, 4 and 5 were classified as susceptible (S). RUM lines (resistant to powdery mildew) and their derivatives are crossed with several susceptible (reaction types 3–5) genotypes and the inheritance of the resistance was studied in the F₁, F₂ and F₃ generations. The results showed that powdery mildew resistance in mungbean is governed by two dominant genes designated as Pm-1 and Pm-2. When both Pm-1 and Pm-2 were present, an R0 reaction was observed after inoculation with TI-1. The resistant reaction was R1 when only Pm-1 was present and R2 in the presence of Pm-2. In the absence of both Pm-1 and Pm-2, susceptible reactions 3, 4 and 5 were observed.     

Differential expression of putative cell death regulator genes in near-isogenic,resistant and susceptible barley lines during interaction with the powdery mildew fungus

We analysed pathogenesis-related expression of genes, that are assumed to be involved in ubiquitous plant defence mechanisms like the oxidative burst, the hypersensitive cell death reaction (HR) and formation of localized cell wall appositions (papillae). We carried out comparative northern blot and RT-PCR studies with near-isogenic barley (Hordeum vulgareL. cv. Pallas) lines (NILs) resistant or susceptible to the powdery mildew fungus race A6 (Blumeria graminis f.sp. hordei, BghA6). The NILs carrying one of the R-genes Mla12, Mlg or the mlo mutant allele mlo5 arrest fungal development by cell wall appositions (mlo5) or a HR (Mla12) or both (Mlg). Expression of an aspartate protease gene, an ascorbate peroxidase gene and a newly identified cysteine protease gene was up-regulated after inoculation with BghA6, whereas the constitutive expression-level of a BAS gene, that encodes an alkyl hydroperoxide reductase, was reduced. Expression of a newly identified barley homologue of a mammalian cell death regulator, Bax inhibitor 1, was enhanced after powdery mildew inoculation. An oxalate oxidase-like protein was stronger expressed in NILS expressing penetration resistance. A so far unknown gene that putatively encodes the large subunit of a superoxide generating NADPH oxidases was constitutively expressed in barley leaves and its expression pattern did not change after inoculation. A newly identified barley Rac1 homologue was expressed constitutively, such as the functionally linked NADPH oxidase gene. Gene expression patterns are discussed with regard to defence mechanisms and signal transduction.     

Redheadia quercus gen. et sp. nov., the teleomorph of Mycopappus quercus, the frosty mildew fungus in Quercus acutissima

The teleomorph of Mycopappus quercus causing frosty mildew in Quercus acutissima is described as a new genus and species, Redheadia quercus, in the Sclerotiniaceae. Apothecia sprout from sclerotia on the fallen infected leaves kept for 10 months at 5°C and subsequent incubation at 15°C under diffused room light. Typical zonate lesions and multicellular propagules of M. quercus are produced on Q. acutissima, by mycelial inoculation using an isolate from a single ascospore, confirming the teleomorph–anamorphic connection. No significant differences are observed between cultured colonies of isolates from the ascospore and those from the propagule. Sclerotia and microconidia of the fungus are produced on culture media.