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| Powdery mildew | |
|---|---|
| Name | Powdery mildew |
| Field | Plant pathology |
| Symptoms | White powdery fungal growth, chlorosis, leaf distortion, premature leaf drop |
| Causal agents | Ascomycete fungi (Erysiphales) |
| Hosts | Wide range of angiosperms including cereals, grapes, roses, cucurbits |
| Treatment | Cultural practices, resistant cultivars, fungicides, biological control |
Powdery mildew is a common group of fungal diseases that affect a wide array of plant species, producing conspicuous white to grayish powdery growth on leaves, stems, flowers, and fruit. It reduces photosynthetic area and can cause yield losses in agriculture, decline in horticultural quality, and aesthetic damage in ornamental gardening. Management integrates host resistance, cultural practices, and targeted chemical or biological controls widely used in agronomy and horticulture.
Affected tissues display a superficial, powdery mycelial mat often consisting of abundant conidia and chasmothecia that appear as white to gray patches on the adaxial and abaxial surfaces. Advanced infections cause chlorosis, necrosis, distorted growth, reduced fruit set, and premature senescence comparable to losses documented in wheat and grapevine production systems. On cultivars of roses, apple, and cucumber symptoms include leaf curling, dwarfing, and reduced marketability that influence decisions in plant breeding and crop management.
The pathogens are obligate biotrophic ascomycetes in the order Erysiphales, with well-known genera such as Blumeria, Erysiphe, Golovinomyces, Leveillula, and Podosphaera. Taxonomic revisions driven by molecular phylogenetics using ITS and LSU rDNA regions have reclassified many species, affecting nomenclature in databases curated by institutions like the Royal Botanic Gardens, Kew and herbaria at Smithsonian Institution. Species complexes (e.g., the Blumeria graminis formae speciales) demonstrate host specificity patterns relevant to experts at the International Maize and Wheat Improvement Center and programmes led by the Food and Agriculture Organization.
Life cycles include asexual sporulation via conidia and sexual reproduction producing chasmothecia (formerly cleistothecia) that enable overwintering and genetic recombination, similar to cycles described for many Ascomycota. Epidemics are driven by airborne conidial dispersal, local humidity regimes, and host phenology; microclimate factors studied in plant pathology research at universities like University of California, Davis and Wageningen University shape outbreak models. Human-mediated movement of infected nursery stock and agricultural trade across regions such as Europe, North America, and Asia contributes to pathogen spread documented by surveillance networks including the European and Mediterranean Plant Protection Organization.
Hosts span diverse angiosperm families, notably Poaceae (cereals), Vitaceae (grapevine), Rosaceae (apple, stone fruits), Cucurbitaceae (melon, cucumber), and Fabaceae. Major crop impacts include yield reductions in wheat by Blumeria, quality losses in wine grapes caused by Erysiphe species, and marketability declines in ornamentals like rose cultivars. Economic assessments performed by institutions like the United States Department of Agriculture and commodity boards quantify direct and indirect costs from fungicide inputs, lost revenue, and quarantine measures.
Diagnosis relies on morphological examination of conidiophores, conidia, and chasmothecia using light microscopy, often supplemented by scanning electron microscopy performed at research centers such as the Scripps Institution of Oceanography for surface imaging. Molecular diagnostics use PCR assays targeting ITS or TEF1 sequences to distinguish species and formae speciales, techniques standardized in laboratories at ICAR institutes and university plant clinics. Differential diagnosis must exclude other foliar disorders documented in manuals published by organizations like the Royal Horticultural Society.
Integrated management prioritizes resistant cultivars developed by breeding programs at institutes such as CIMMYT and INRAE, cultural practices that reduce canopy humidity (pruning, spacing), sanitation to remove inoculum, and monitoring via regional advisory services like extension programs at Cornell University. Quarantine, seed and nursery certification, and forecasting models used by agricultural agencies help mitigate introduction and establishment in production regions including California Central Valley and Mediterranean Basin.
Biological control employs antagonists and microbial biopesticides (e.g., Bacillus subtilis strains, mycoparasites) evaluated in trials at CSIRO and university research stations; induced resistance using chitosan or plant defense elicitors is an active research area in institutes such as INRAE and ETH Zurich. Chemical control relies on site-specific fungicides including demethylation inhibitors, QoI fungicides, and SDHIs, with resistance management strategies coordinated by bodies like the FRAC and implemented in commodity-specific guidelines from organizations such as the Australian Pesticides and Veterinary Medicines Authority. Sustainable programs combine timing, rotation of modes of action, and integration with non-chemical tactics promoted by extension services at University of Florida and Washington State University.
Category:Fungal plant pathogens and diseases