Erysiphales are an order of

ascomycete Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

. The order contains one family, Erysiphaceae. Many of them cause plant diseases called

powdery mildew Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as ...

Systematics

The order contains one

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

(Erysiphaceae), 28

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

and approximately 100

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. Many

imperfect fungi The fungi imperfecti or imperfect fungi, are fungi which do not fit into the commonly established Taxonomy (biology), taxonomic classifications of fungi that are based on biological species concepts or morphological characteristics of sexual str ...

(fungi whose sexual reproduction is unknown) belong here, especially the genus '' Oidium''. Recent

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

data have revealed the existence of six main evolutionary lineages.

Clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

1 consists of ''

Erysiphe ''Erysiphe'' is a genus of fungi in the family Erysiphaceae. Many of the species in this genus are plant pathogens which cause powdery mildew. Species This genus includes, but is not limited to the following species: * ''Erysiphe alphitoides'' * ...

'', ''

Microsphaera ''Microsphaera'' is a genus of powdery mildew in the family Erysiphaceae Erysiphales are an order of ascomycete fungi. The order contains one family, Erysiphaceae. Many of them cause plant diseases called powdery mildew. Systematics The or ...

'', and ''

Uncinula ''Uncinula'' is a genus of fungi. Its species are plant pathogens that cause powdery mildew diseases on various plant hosts. The genus is characterized by its dark chasmothecia which bear filamentous, hyaline appendages with hooked tips. Over o ...

'', all of which have an ''Oidium'' subgenus ''Pseudoidium''

mitosporic The fungi imperfecti or imperfect fungi, are fungi which do not fit into the commonly established taxonomic classifications of fungi that are based on biological species concepts or morphological characteristics of sexual structures because thei ...

state. Clade 2 consists of '' Erysiphe galeopsidis'' and '' Erysiphe cumminsiana'' (

anamorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

s in ''Oidium'' subgenus ''Striatoidium''). Clade 3 consists of ''Erysiphe'' species with anamorphs in ''Oidium'' subgenus ''Reticuloidium''. Clade 4 consists of ''Leveillula'' and ''Phyllactinia'', which have ''Oidiopsis'' and ''Ovulariopsis'' mitosporic states, respectively. Clade 5 consists of '' Sphaerotheca'', ''Podosphaera'', and ''Cystotheca'', which have ''Oidium'' subgenera ''Fibroidium'' and ''Setoidium'' mitosporic states. Clade 6 consists of ''

Blumeria graminis ''Blumeria graminis'' (commonly called barley powdery mildew or corn mildew) is a fungus that causes powdery mildew on grasses, including cereals. It is the only species in the genus ''Blumeria''. It has also been called ''Erysiphe graminis'' and ...

'', which has an ''Oidium'' subgenus ''Oidium'' mitosporic state. Several morphological characters have been analysed and found not to conflict with the molecular data.

Characteristics

*Erysiphales have a superficial

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...

which extracts nourishment from the host plant through specialized

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e that penetrate the

epidermal The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...

cells of the host by means of absorbing organs called

haustoria In botany and mycology, a haustorium (plural haustoria) is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates t ...

. *The

teleomorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

s are usually more distinctive and diverse than the anamorphs. Whether the asci are bitunicate or unitunicate (i.e. consisting of one or two layers), is as yet a matter of discussion. *The

cleistothecia An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are ...

(or ''chasmothecia'') have the asci arranged in a hymenial layer, resembling

perithecia An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mo ...

. The cleistothecia are minute, usually not much more than in diameter. From the outer wall of the cleistothecium specialised hyphae (appendages) grow out. The number of asci per

ascoma An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mo ...

varies, and is important in discriminating between genera. *Erysiphales are notable for intricate

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

s which follow

fractal In mathematics, a fractal is a geometric shape containing detailed structure at arbitrarily small scales, usually having a fractal dimension strictly exceeding the topological dimension. Many fractals appear similar at various scales, as illu ...

geometry within

Fibonacci number In mathematics, the Fibonacci numbers, commonly denoted , form a sequence, the Fibonacci sequence, in which each number is the sum of the two preceding ones. The sequence commonly starts from 0 and 1, although some authors start the sequence from ...

s and can be useful for species identification.

Life cycle

The infection of the host plant begins with the sexual

ascospores An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or ...

, or the asexual

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

germinating on the surface of the plants leaf or stem, resulting in

septate In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatr ...

mycelium of

uninucleate {{Short pages monitor