The past decade has seen fundamental changes in our understanding of powdery mildews (Erysiphales). Research on molecular phylogeny demonstrated that Erysiphales are Leotiomycetes (inoperculate discomycetes) rather than Pyrenomycetes or Plectomycetes. Life cycles are surprisingly variable, including both sexual and asexual states, or only sexual states, or only asexual states. At least one species produces dematiaceous conidia. Analyses of rDNA sequences indicate that major lineages are more closely correlated with anamorphic features such as conidial ontogeny and morphology than with teleomorph features. Development of molecular clock models is enabling researchers to reconstruct patterns of coevolution and host-jumping, as well as ancient migration patterns. Geographic distributions of some species appear to be increasing rapidly but little is known about species diversity in many large areas, including North America. Powdery mildews may already be responding to climate change, suggesting they may be useful models for studying effects of climate change on plant diseases.

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A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or chasmothecia that were collected from grape leaves with a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique sequences of the internal transcribed spacer regions of E. necator. Using these primers in PCR amplifications, a 367-bp amplicon specific to E. necator was generated, but no amplicons were generated from other erysiphaceous species collected from 48 disparate hosts representing 26 vascular plant families. The PCR limit of detection was one to five conidia of E. necator placed directly into reaction mixtures or 100 to 250 conidia placed on glass rods coated with silicon grease. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. Amplification of E. necator DNA did not occur when the PCR assay was conducted on vineyard air samples collected while grapes were dormant or during periods when vine growth occurred but E. necator remained dormant. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the 3 years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this study represent the initial step toward the goal of incorporating an inoculum availability component into current and future grapevine powdery mildew risk assessment models.

The taxonomy of the powdery mildew fungus infecting lentil in the Pacific Northwest (PNW) of the United States was investigated on the basis of morphology and rDNA internal transcribed spacer (ITS) sequences. Anamorphic characters were in close agreement with descriptions of Erysiphe trifolii. However, teleomorphs formed chasmothecial appendages with highly branched apices, whereas E. trifolii has been described as producing flexuous or sometimes loosely branched appendages. Branched appendages have been described in Erysiphe diffusa, a fungus reported from species of Lens, Glycine, and Sophora, raising the possibility that the PNW fungus could be E. diffusa. Examination of morphological characters of an authentic specimen of E. trifolii from Austria determined that it included chasmothecial appendages resembling those seen in PNW specimens. Furthermore, ITS sequences from five powdery mildew samples collected from lentils in PNW greenhouses and fields from 2006 to 2008 were identical to one another, and exhibited higher similarity to sequences of E. trifolii (99%) than to those of any other Erysiphe spp. available in GenBank. Parsimony analysis grouped the lentil powdery mildew into a clade with Erysiphe baeumleri, E. trifolii, and E. trifolii–like Oidium sp., but indicated a more distant relationship to E. diffusa. In greenhouse inoculation studies, the lentil powdery mildew fungus did not infect soybean genotypes known to be susceptible to E. diffusa. The pathogenicity of E. trifolii on lentil was confirmed using modified Koch's postulates. This is the first report of E. trifolii infecting lentil. E. diffusa and E. trifolii have different host ranges, so the discovery of E. trifolii on lentil has implications both for determining species of powdery mildews on cool-season grain legumes, and in disease management.

Diversity of powdery mildew pathogens infecting pea (Pisum sativum) in the US Pacific Northwest was investigated using both molecular and morphological techniques. Phylogenetic analyses based on rDNA ITS sequences, in combination with assessment of morphological characters, defined two groups of powdery mildews infecting pea. Group I (five field samples and three glasshouse samples) had ITS sequences 99% similar to those of Erysiphe pisi in GenBank and exhibited simple, mycelioid type of chasmothecial appendages typical of E. pisi. Erysiphe pisi is normally considered as the powdery mildew pathogen of pea. Group II (four glasshouse samples and two field samples) had ITS sequences 99% similar to those of E. trifolii and produced chasmothecia with dichotomously branched appendages similar to those of E. trifolii. There are fourteen nucleotide differences in the ITS region between the two groups. The correlation of rDNA ITS sequences with teleomorphic features for each of the two groups confirms their identity. Repeated samplings and artificial inoculations indicate that both E. pisi and E. trifolii infect pea in the US Pacific Northwest. Erysiphe trifolii is not previously known as a pathogen of pea. The existence of two distinct powdery mildew species infecting pea in both glasshouse and field environments may interfere with the powdery mildew-resistance breeding programmes, and possibly explains putative instances of breakdown of resistance in previously resistant pea breeding lines.

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Cultures and anamorphs of six species of Diatrype and Diatrypella are described. Diatrypella favacea produces conidia from sympodially proliferating conidiogenous cells, whereas Diatrype stigma produces conidia from percurrently proliferating (annellated) conidiogenous cells. Both of these types of conidiogenous cell proliferation were found in Diatrypella verrucaeformis, Diatrypella pulvinata, Diatrype virescens, and Diatrype albopruinosa. Both the sympodial and percurrent modes of conidiogenous cell proliferation appear to be associated with holoblastic conidiogenesis.

Yeasts were isolated from grapes collected from a research vineyard at the WSU-IAREC, located at Prosser, WA. Species determination was based on cultural features, microscopic morphology, physiological tests and analysis of ITS and D1/D2 rDNA sequence data. Fifty-three species were found distributed among five fungal subphyla, a greater number than expected based on similar published studies. Within Saccharomycotina, 13 species in the genera Candida, Hanseniaspora, Metschnikowia, Meyerozyma, Pichia, Wickerhamomyces and Yamadazyma were determined. Isolates within the Metschnikowia pulcherrima clade appeared to possess considerable diversity. Pucciniomycotina was represented by 12 species, in Curvibasidium, Rhodosporidium, Rhodotorula, Sporidiobolus and Sporobolomyces. Five phylogenetically distinct species in the subphylum could not be assigned to any described species. Isolates in Ustilaginomycotina were placed in Pseudozyma except for a single strain determined to be Rhodotorula bacarum. Within Agaricomycotina, 17 species in the genera Cryptococcus, Cystofilobasidium, Hannaella, Holtermanniella and Mrakiella were determined. Seven species of yeastlike Pezizomycotina were found, representing classes Leotiomycetes, Dothideomycetes and Sordariomycetes. Isolates of Aureobasidium pullulans represented three phylogenetically distinct subspecific lineages. Seventeen species identified in this study were previously unreported from wine grapes and 18 species were unreported from North America. Several strains appear to represent undescribed species, including the recently described Curvibasidium rogersii.