| Powdery mildews | |
|---|---|
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| Golovinomyces sordidus demonstrating typical white patches on a leaf ofPlantago major | |
Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Leotiomycetes |
| Order: | Helotiales |
| Family: | Erysiphaceae Tul. &C.Tul., 1861 |
Erysiphaceae (commonly known aspowdery mildews) is a family ofascomycete fungi in the orderHelotiales. The members of this family are obligate parasites with a superficialmycelium that forms a characteristic white, powdery coating on theirhost plants.
The family contains seventeengenera and around a thousandspecies.[1] Combined they infect over 10,000 species ofplants, many of which are commercially valuable.[2]
Powdery mildews exist in two states, the asexualanamorph state reproducing by means ofconidia, and the sexualteleomorph state reproducing by means ofascospores produced inasci developing in more or less sphericalchasmothecia. The ripe spores become detached and are readily dispersed by the wind, causing fresh infection. The usually conspicuous whitish mycelium and conidiophores on leaves, and sometimes on stems, fruits or even petals, are what is generally seen first. The chasmothecia are usually visible to thenaked eye and turn from translucent or yellow-orange to purple or black. They are produced on the mycelium later in the season, though may be absent. Upon reaching maturity the chasmothecia may develop hair‐like appendages that may branch in characteristic ways.[3]
The mycelium can appear in varying degrees of thickness and patchiness, on leaves, petioles, stems, twigs, fruits or flowers. On leaves, mycelium can beepiphyllous (on leaf uppersides), hypophyllous (on leaf undersides) or amphigenous (on both sides).Phyllactinia in particular is characterised by hypophyllous mycelium, although members of other genera also infect only the leaf undersides.
Erysiphaceae species are occasionally also associated with galls. For example,Podosphaera phytoptophila is one of the causers ofwitch's broom galls on hackberry (Celtis occidentalis). Although not fully understood, it is believed that a minute, wormlike, eriophyid mite (Aceria celtis) induces the brooms andP. phytoptophila exploits the weakened plant and favourable habitat created by deformed buds and dense branching.[4]Cystotheca lanestris is also known as a North American gall-former, on variousQuercus species.[5]
The similarly-named but unrelateddowny mildews (Peronosporaceae) can have a similar appearance to powdery mildews, however growth is always on the underside of leaves, often causing yellowing on the upperside. The mycelium of these members of thePeronosporales is internal in the plant tissue and thesporangiophores (more or less equivalent to conidiophores) emerge through thestomata; in the Peronosporaceae the sporangiophores are elongated and branched above so that the colonies are downy or felt‐like and usually greyish in colour.[3]
Erysiphaceae species areobligate biotrophs, meaning they infect living plants. Specialised haustoria are able to penetrate the plant cells while keeping them alive. Most powdery mildew species are highly host-specific, infecting at most a few genera and frequently just a single species. The few species that are still rather broadly defined are considered species complexes with a narrowsensu stricto host range. Despite this, they are capable of 'jumping' host to infect a new genus. It is thought the now-common species in EuropeErysiphe alphitoides did this to first infect oaks (Quercus), facilitating its spread to the continent. Since then, it has also been reported as occurring on plants such asWisteria, demonstrating the host-jumping ability that has lead to its success.[6][7]
Some Erysiphaceae species host thehyperparasiteAmpelomyces quisqualis.[8] This fungus reduces growth and may even kill the mildew, leading to its use as an active ingredient in some fungicides. Around 40 other fungal species have been known to parasitise powdery mildews: mainly ascomycetes such asCladosporium but including basidiomycetes such asTilletiopsis.[9]
Erysiphaceae have a cosmopolitan distribution and are native to every continent other thanAntarctica andAustralia.[10] The centre of biodiversity appears to be inEast Asia,[11] and many species have beenintroduced from here to other continents such asEurope andNorth America, often due to trade in plants for gardens. Some powdery mildew species can become invasive when introduced outside their native range.[12]
As well as a circumglobal distribution, powdery mildews are also found in any and all habitats with enough vascular plants to sustain a population. While the diversity of powdery mildews in some areas (such asWestern Europe) has been well-studied, there are undescribed species in all regions of the world, with the diversity of some areas such as much ofAfrica still little-known.
While the benchmark for fungal identification remains the two-step combination ofmicroscopy andDNA sequencing, a great many powdery mildew species can be identified in the field with a combination of host plant information and visible characteristics such as colour and texture.
Due to the fact that all powdery mildew species are to some extent host-specific (most are highly restricted to only a single genus or even species) host plant identification is vital for identification in the field or often under the microscope. Some powdery mildew species even have identicalITS sequences,[13] meaning host plant information is still necessary even when the specimen is sequenced.
Distinguishing characteristics in the field or from photos include the location of the infection on the plant, including what side of the leaf it infects; the thickness and colour of the mycelium; and sometimes the appearance and colour ofchasmothecia if present. Under the microscope, a key characteristic to determine between genera is the presence or absence offibrosin bodies in the conidia. Other characteristics useful for identification are the shape and length ofconidia, whether they are single or on conidiophores, the shape ofappresoria, and the appearance of chasmothecialappendages.[3]
Some cultivars of both vegetables and ornamental plants are bred to be resistant to powdery mildews. Powdery mildew thrives particularly in areas with little air flow, dry host leaves and humid conditions.[14] As a result, it is important to manage the environment around susceptible plants by: avoiding sheltered places, such as against walls or fences, where the air is likely to be still; providing good drainage, but watering regularly during dry periods (plants suffering from regular but intermittent drought-stress are more susceptible); not planting too densely, giving space between plants; and pruning shrubs to give an open structure improving air circulation and humidity. Application of mulch may help water retention. It is also recommended not to over-fertilise (especially not too much nitrogen) as succulent growth is particularly susceptible to infection.[15]
Especially on an industrial scale, powdery mildew infections can be managed by the application of fungicides.[16] Spray programs of conventional fungicides are advised to begin when powdery mildew symptoms and signs are first noticed. Conventional fungicides should be applied on a regular basis for best results against the disease, although in some species there is a high risk of fungicide resistance.[17] Another effective prevention method is through genetic resistance. For example, combinations of variations of the Pm3 allele has been shown to provide improved protection against powdery mildew infection.[18]
Several unconventional methods of chemical control have been tested to varying degrees of success. Some commonly reported methods include milk, sulphur, potassium bicarbonate, metal salts and oils.[19][20]Neem oil is said to effectively manage powdery mildew on many plants by interfering with the fungus' metabolism and terminating spore production. Milk has been proven effective at treating powdery mildew on some greenhouse crops,[21] potentially becauseferroglobulin, a protein inwhey, produces oxygenradicals when exposed to sunlight, and contact with these radicals is damaging to the fungus. Another unconventional chemical treatment involves treating with a solution ofcalcium silicate.[22] Silicon reportedly helps defend plants against fungal attack by degradinghaustoria and by producingcallose andpapilla.
Powdery mildews are thought to have first evolved in theLate Cretaceous,[23] and have evolved with their host plants for millennia. The most ancestral genera of the family,Paraunicnula andCaespitotheca, are theorised to have evolved in theNorthern Hemisphere and migrated southward with their hosts, leading to relict populations in South America and East Asia.[23] These two genera have multiple features in common, including uncinulate-circinate appendage tips andwoody host plants. This suggests that powdery mildews likely first evolved with this micromorphology infecting woody host plants, and since branched out to infectherbaceous plants.[24][25]
The first description of a powdery mildew species came fromLinnaeus in his 1753 workSpecies Plantarum, combining infections on multiple hosts includingHumulus,Acer,Lamium,Galeopsis, andLithospermum as one species under the nameMucor erysiphe. The first authors to extensively describe powdery mildews werede Candolle andWallroth in the early 1800s, although many of their species would then be lumped into just 16 by Fries, all in the genusErysiphe.[26] The first monograph of the group was published bySalmon in 1900. By the time of Uwe Braun's 1987 monograph, many more species and genera had been described, although following Braun and Cook's landmark publication of theTaxonomic Manual of the Erysiphales in 2012 some of the genera needed to be absorbed due to the 'one fungus one name' rule implemented the same year.[27] As a result of this change to theCode,anamorph genera are no longer accepted. However, some species have not yet been reassigned to their correct teleomorph genus, while some are not known in the teleomorph state. Many anamorphic mildew species were formerly placed in the genusOidium. Many of these are now correctly placed in different genera, although some have not yet been assigned to a new genus. A process that had already begun by the time Braun and Cook's treatment came out – the transformation of taxonomy using genomic DNA – has accelerated, especially in the past half-decade for powdery mildews, leading to many new species described.
The following list of genera is that accepted by Shirouzu et al. (2020)[1] updated to reflect Bradshaw et al. (2025).[28]
A monotypic genus containing the speciesArthrocladiella mougeotii, which infects species in the genusLycium.[29]
(Oidium sensu stricto) – often has thick growth and densely packed chasmothecia, and is restricted to grass hosts (Poaceae).[30]
Brasiliomyces comprises four species with small, semitransparent chasmothecia with single-layered peridia.[31]
One species, with sparse mycelium loosely spreading on both surfaces ofBauhinia.[32]
An ancestral monotypic genus containing the speciesCaespitotheca forestalis, infectingSchinopsis.[33]
(formerly with the anamorphSetoidium) –Cystotheca causes witch's-brooms and shoot damage, specialising mostly on oaks and relatives (Fagaceae).[34]
(formerly with the anamorphPseudoidium) –Erysiphe is a highly diverse genus, found worldwide on a wide array of host plants, particularly in warm-temperate climes.[35][36][37]
(formerly with the anamorphEuoidium) –Golovinomyces contains greyish-white species that are often seen in the autumn and have a diverse host range on herbs and forbs.[38]
Microidium (named after its tiny conidiophores and conidia) is only found onPhyllanthaceae.[39]
(formerly with the anamorphStriatoidium) – Similarly toGolovinomyces,Neoerysiphe consists of greyish-white species that are often seen in the autumn and have a diverse host range on herbs and forbs; it develops ascospores after a cold period (stratification).[40]
Parauncinula is the earliest-diverging genus in the Erysiphaceae, endemic to East Asia and infecting hosts in theFagaceae. It consists of four species.[41]
Phyllactinia consists of three sections, two of which were formerly considered separate genera: sect.Leveillula, sect.Phyllactinia, and sect.Basiphyllactinia. SectionLeveillula formerly had the anamorph genusOidopsis and consists of two main groups found on herbs and shrubs. One produces bright white cottony or puffy tufted mycelium often on host plants' stems, and the other produces weak feathery or fluffy mycelium often on host plants' leaves. SectionPhyllactinia, some species formely included in the anamorph genusOvulariopsis, is mostly found on shrubs and trees and produces smooth weak pale mycelium on leaf undersides. SectionBasiphyllactinia is found on various forbs, shrubs, and trees, and produces usually thick dense colourful mycelium on lower or both sides of leaves.[28]
Pleochaeta (with anamorphs formerly part ofStreptopodium orOvulariopsis) is found on trees or forbs and produces fluffy mycelium, very faint to sometimes dense, mainly on leaf undersides.Queirozia has been reduced to synonymy with this genus.[28]
(formerly with the anamorphFibroidium) –Podosphaera is common, especially on roses and related fruit trees (Rosaceae), and frequently twists and distorts leaves and shoots.[9]
The genusSalmonomyces was resurrected in 2020. The genus includes two species:Salmonomyces acalyphae andSalmonomyces javanicus.[42]
(formerly with the anamorphOctagoidium) –Sawadaea is common on maples and their relatives (Sapindaceae), forming spreading mats on leaves.[43]
Similarly toSawadaea,Takamatsuella is fairly common on maples and has similar macromorphology.[43]
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