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| Oidium (fungus) | |
|---|---|
| Name | Oidium |
| Regnum | Fungi |
| Divisio | Ascomycota |
| Classis | Leotiomycetes |
| Ordo | Erysiphales |
| Familia | Erysiphaceae |
| Genus | Oidium (sensu auct.) |
| Subdivision ranks | Species |
Oidium (fungus) is a historical and practical morphotype name applied to anamorphic stages of powdery mildew fungi within the order Erysiphales. Once used in classical mycological literature and phytopathological practice, the term Oidium denoted asexual conidial stages observed on host tissues and referenced in diagnostics, quarantine, and crop protection literature. Modern taxonomy increasingly assigns these anamorphs to teleomorphic genera based on molecular phylogenetics and type-species concepts.
The label Oidium originated in Linnaean-era mycology and featured in major taxonomic treatments such as those by Elias Magnus Fries, August Carl Joseph Corda, and later authors compiling floras for United Kingdom, Germany, and United States. Taxonomic revision driven by gene regions (ITS, LSU, SSU) and multilocus analyses from institutes like Royal Botanic Gardens, Kew, Max Planck Society, and Smithsonian Institution reassign many Oidium anamorphs to teleomorph genera including Erysiphe, Podosphaera, Sphaerotheca, Leveillula, and Golovinomyces. Nomenclatural changes have been affected by international codes negotiated at International Botanical Congress sessions and implemented by committees such as the International Mycological Association. Historical monographs and exsiccatae curated at herbaria like Royal Botanic Gardens, Kew Herbarium, The New York Botanical Garden Herbarium, and Muséum National d'Histoire Naturelle preserve Oidium-type specimens.
Oidium anamorphs characteristically produce chains of hyaline, single-celled conidia on superficial mycelium; these structures were described in classical keys used by practitioners at institutions including Royal Horticultural Society, United States Department of Agriculture, and Institut National de la Recherche Agronomique. Conidiophores, conidia, and chasmothecia (cleistothecia in older literature) are morphological characters integrated into life-cycle models discussed in texts from University of California, Davis, Cornell University, and Wageningen University. Sexual stages assigned to genera such as Erysiphe produce asci and ascospores within chasmothecia, enabling overwintering and long-distance dispersal documented in studies by CABI and research groups at ETH Zurich. Molecular clocks calibrated against fossils and sequence data from centers like Sanger Institute inform timing of diversification among Erysiphales clades.
Historically, Oidium anamorphs have been reported from a broad spectrum of hosts in agriculture and horticulture: cereals, vines, fruits, ornamentals and vegetable crops. Hosts and pathosystems appear in extension literature from University of Florida, Iowa State University, and Australian Department of Agriculture and in pest datasheets by Food and Agriculture Organization. Pathogenic interactions on species such as grapevine, cereal crops, cucurbits, and rosaceous ornamentals involve host-specific lineages described in monographs by International Organisation for Biological and Integrated Control of Noxious Animals and Plants (IOBC) and trial results reported at conferences like International Congress of Plant Pathology. Symptoms include superficial white mycelial mats, chlorosis, and reduced photosynthetic capacity referenced in applied guides from Rothamsted Research and CSIRO.
Anamorphic Oidium stages are distributed worldwide, with records in floras and plant health reports from regions including Europe, North America, South America, Africa, Asia, and Oceania. Environmental conditions favoring epidemics—moderate temperatures, high humidity but low leaf wetness—are detailed in climatic studies by Met Office, National Oceanic and Atmospheric Administration, and regional plant clinics affiliated with Universidad de São Paulo and Peking University. Dispersal dynamics involve airborne conidia, human-mediated movement via nursery trade regulated under protocols by World Trade Organization phytosanitary measures and International Plant Protection Convention standards. Interactions with biocontrol agents, hyperparasites, and endophytes are subjects of research at INRAE and universities such as University of California, Berkeley.
Traditional diagnosis of Oidium relied on light microscopy of conidia and conidiophores using keys from herbaria and manuals produced by Royal Botanic Gardens, Kew, USDA ARS, and FAO. Modern identification integrates ITS sequencing, multilocus sequence typing, and phylogenetic placement performed in laboratories at Wellcome Sanger Institute and university molecular facilities; results are compared against databases maintained by GenBank, MycoBank, and Index Fungorum. Diagnostic workflows used by plant health services at Defra and Canadian Food Inspection Agency combine symptom assessment, microscopy, culture, and molecular assays, often employing PCR primers standardized in collaborative studies published through European and Mediterranean Plant Protection Organization.
Control strategies for Oidium-type powdery mildews encompass cultural practices, resistant cultivars, chemical fungicides, and biological control. Cultural measures advocated by extension services at University of Minnesota, Pennsylvania State University, and CSIRO include canopy management, sanitation, and crop rotation. Breeding programs at institutions such as INRAE, University of California, Davis, and John Innes Centre deploy resistant germplasm and marker-assisted selection. Fungicide programs use active ingredients evaluated in trials by IRAC collaborators and registered via regulatory bodies like European Chemicals Agency and Environmental Protection Agency. Biocontrol agents and integrated pest management protocols are promoted by FAO and trialed in projects funded by organizations such as Bill & Melinda Gates Foundation.
Oidium-associated powdery mildews cause yield losses, quality downgrades, and increased management costs in vineyards, orchards, vegetable production, and ornamentals. Economic assessments by agencies including USDA Economic Research Service, Food and Agriculture Organization, and national ministries of agriculture document impacts on commodity markets, supply chains, and export certification processes overseen through World Trade Organization agreements. Crop-specific losses and cost–benefit analyses appear in reports from International Food Policy Research Institute, Rothamsted Research, and commodity boards like California Table Grape Commission and Wine Australia.
Category:Powdery mildew fungi