Peronosporaceae are a

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 ...

water mould Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the r ...

s that contains 21

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 ...

, comprising more than 600

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 ...

. Most of them are called

downy mildew Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to the Peronosporaceae family. In commercial agriculture, they are a particular problem for growers of crucif ...

s. Peronosporaceae are obligate biotrophic

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

s. They parasitise their host plants as an intercellular

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 ...

using

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 ...

to penetrate the host cells. The downy mildews reproduce asexually by forming

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

on distinctive white sporangiophores usually formed on the lower surface of infected leaves. These constitute the "downy mildew". The sporangia are wind-dispersed to the surface of other leaves. According to the genus concerned, the sporangia may then germinate by forming

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s, thus resembling ''Phytophthora'', or by germ-tube. In the latter case, the sporangia behave as

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 ...

and are often referred to as such.

Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

is via

oospore An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes. They are believed to have evolved either through the fusion of two species or the chemically-induced stimulation of mycelia, ...

s. The parasitised plants are

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

gymnosperms The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό� ...

, and most Peronosporaceae are pathogens of herbaceous dicots. Some downy mildew genera have a more restricted host range, e.g. ''

Basidiophora ''Basidiophora'' is a genus of oomycetes belonging to the family Peronosporaceae Peronosporaceae are a family of water moulds that contains 21 genera, comprising more than 600 species. Most of them are called downy mildews. Peronosporaceae ...

'', '' Paraperonospora'', '' Protobremia'' and '' Bremia'' on

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

; '' Perofascia'' and ''

Hyaloperonospora ''Hyaloperonospora'' is a genus of oomycete, obligate, plant pathogens that was originally considered to be part of ''Peronospora''. Species in this group produce a disease called downy mildew and can infect many important crops. From the 19 down ...

'' almost only on

Brassicaceae Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The le ...

; ''

Viennotia ''Viennotia'' is a monotypic genus of oomycete belonging to the family Peronosporaceae. It only contains one known species; Viennotia oplismeni (Vienn.-Bourg.) Göker, Voglmayr, Riethm., M. Weiss & Oberw. (2003) The genus was circumscribed by M ...

'', ''

Graminivora ''Graminivora'' is a monotypic genus of oomycete belonging to the family Peronosporaceae Peronosporaceae are a family of water moulds that contains 21 genera, comprising more than 600 species. Most of them are called downy mildews. Peronospo ...

'', '' Poakatesthia'', '' Sclerospora'' and '' Peronosclerospora'' on

Poaceae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

, and '' Plasmoverna'' on

Ranunculaceae Ranunculaceae (buttercup or crowfoot family; Latin "little frog", from "frog") is a family of over 2,000 known species of flowering plants in 43 genera, distributed worldwide. The largest genera are ''Ranunculus'' (600 species), ''Delphinium' ...

. The largest genera, ''

Peronospora ''Peronospora'' is a genus of oomycetes that are obligate plant pathogens of many eudicots. Most species in this group produce a downy mildew disease, which can cause severe damage to many different cultivated crops, as well as wild and ornamenta ...

'' and ''

Plasmopara ''Plasmopara'' is a genus of Oomycota. ''Plasmopara'' species are plant pathogens, causing downy mildew on carrot, parsley, parsnip, chervil Chervil (; ''Anthriscus cerefolium''), sometimes called French parsley or garden chervil (to disting ...

'', have a very wide host range. Peronosporaceae of economic importance include those that infect

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years ago, ...

vines (''

Plasmopara viticola ''Plasmopara viticola'', the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition release ...

'') and

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

(''

Peronospora tabacina ''Peronospora hyoscyami'' f.sp. ''tabacina'' is a plant pathogen infecting tobacco that causes blue mold. It is an oomycete (a fungus-like organism) that is highly destructive toward seed plants. It is very prevalent in humid farming zones, ...

''; blue mould). The latter species has such delicate spores that it times its spore release for

sunrise Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning. The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects. Terminology Al ...

, a time of high ambient moisture and

dew Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at wh ...

accumulation, so that its spores are less likely to succumb to desiccation and light. '' Bremia lactucae'' is a parasite on

lettuce Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, ...

, '' Plasmopara halstedii'' on

sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...

References

* C. J. Alexopolous, Charles W. Mims, M. Blackwell ''et al.'', ''Introductory Mycology, 4th ed.'' (John Wiley and Sons, Hoboken NJ, 2004) (may be a bit outdated) * * Thines, M., Voglmayr, H. & Göker, M. ''Taxonomy and phylogeny of the downy mildews (Peronosporaceae)''. In: Lamour, K. & Kamoun, S. (eds.), Oomycete genetics and Genomics (John Wiley and Sons, Hoboken NJ, 2009), pp. 47–55. {{Taxonbar, from=Q621759 Peronosporales Heterokont families