Albugo
Encyclopedia
Albugo is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of oomycetes which are not true fungi (Eumycota), although many discussions of this organism still treat it as a fungus. The taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 of this genus is incomplete, but several species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 are plant pathogens. Albugo is one of three genera currently described in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Albuginaceae, the taxonomy of many species is still in flux.

This organism causes white rust
Rust (fungus)
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing...

 or white blister diseases in above-ground plant tissues. While these organisms affect many types of plants, the destructive aspect of infection is limited to a few agricultural crops.

Some species of the Albuginaceae

  • Wilsoniana bliti
    Albugo bliti
    Albugo bliti, White Rust, is a type of oomycete pathogen of genus Albugo that affects the tissues of plants. In particular, this white rust is found on Amaranth, beets, and lambs quarters. Many discussions of this white rust treat it as a type of fungus....

    and Wilsoniana amaranthi, White rusts of Amaranth.
  • Albugo candida
    Albugo candida
    White rust, Albugo candida is a species from family Albuginaceae; however, all the other species in this family are called "white rust." Like other water moulds which are plant pathogens, it is sometimes called a fungus, although water moulds are not classified in the kingdom Fungi.Synonyms:*...

    , White rust of several Brassicaceae
    Brassicaceae
    Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....

  • Albugo ipomoeae-panduratae
    Albugo ipomoeae-panduratae
    Albugo ipomoeae-panduratae, White Rust, is an oomycete plant pathogen, although many discussions still treat it as a fungal organism.- External links :**...

    , White rust, parasitic to some Convolvulaceae
    Convolvulaceae
    Convolvulaceae, known commonly as the bindweed or morning glory family, are a group of about 60 genera and more than 1,650 species of mostly herbaceous vines, but also trees, shrubs and herbs.- Description :...

    .
  • Albugo occidentalis
    Albugo occidentalis
    Albugo occidentalis, Spinach White Rust, is an oomycete plant pathogen, although some discussions still treat it as a fungal organism.- External links :**...

    , Spinach white rust.
  • Wilsoniana platensis, White rust of some ornamentals (e.g. Boerhavia).
  • Wilsoniana portulaceae, White rust of portulac (Portulaca oleracea)
  • Pustula tragopogonis
    Albugo tragopogonis
    Albugo tragopogonis, Sunflower White Rust, is an oomycete plant pathogen, although some sources still regard it as a fungal organism.Albugo tragopogonis is the old name for Pustula tragopogonis, the causal agent of white blister disease on goatsbeard...

    , white rust of goatsbeard (Tragopogon). Often, sunflower white rust caused by Pustula helianthicola was also attributed to this species.
  • Albugo laibachii, White rust specialised to Arabidopsis
    Arabidopsis
    Arabidopsis is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress , one of the model organisms used for studying plant biology and the first plant to have its entire genome sequenced...

     species.

Summary

White Rust plant disease caused by the Albugo spp. fungal-like pathogen should not be confused with White Pine Blister Rust, Chrysanthemum White Rust or any fungal rusts, all of which are also plant diseases but have completely different symptoms and causal pathogens. Symptoms of white rust caused by Albugo spp. typically include yellow lesions on the upper leaf surface and white pustules on the underside of the leaf. The pathogen is spread by wind, water, and insects. Management includes use of resistant cultivars, proper irrigation practices, crop rotation, sanitation, and chemical control. White Rust is an important economic disease, causing severe crop losses if not controlled.

Hosts & Symptoms

White Rust pathogens create chlorotic (yellowed) lesions and sometimes galls on the upper leaf surface and there are corresponding white blister-like dispersal pustules of sporangia on the underside of the leaf. Species of the Albuginaceae deform the branches and flower parts of many host species. Host species include most if not all plants in the Brassicaceae Family, common agricultural weeds, and those specified above.
http://web.aces.uiuc.edu/vista/pdf_pubs/960.PDF

Disease Cycle

White Rust is an obligate parasite. This means it needs a living host to grow and reproduce. The Albuginaceae reproduce by producing both sexual spores called oospores and asexual spores called sporangia in a many-stage (polycyclic) disease cycle.

The thick-walled oospores are the main overwintering structures, but the mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...

 can also survive in conditions where all the plant material is not destroyed during the winter. In the spring the oospores germinate and produce sporangia (s. sporangium) on short stalks called sporangiophores that become so tightly packed within the leaf that they rupture the epidermis and are consequently spread by the wind. The liberated sporangia in turn can either germinate directly with a germ tube
Germ tube
A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination.The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae....

 or begin to produce biflagellate motile zoospores. These zoospores then swim in a film of water to a suitable site and each one produces a germ tube - like that of the sporangium - that penetrates the stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...

. When the oomycete has successfully invaded the host plant, it grows and continues to reproduce.

Environment

Favorable conditions for the dispersal and consequent infection of White Rust from diseased to healthy plants are most common in the autumn and spring seasons. This pathogen prefers cool, moist conditions for the spread and formation of new infections. Conversely, it rarely infects in warm, dry conditions. Albugo spp. are very temperature sensitive, with the optimal temperature range for infection between 55 F and 77 F. The likelihood of germination and infection is considerably lower if temperatures deviate too far outside this optimum range.
http://web.aces.uiuc.edu/vista/pdf_pubs/960.PDF

Light rain or irrigation lasting for extended periods of time is also ideal for disease development. Leaf surfaces need to remain wet for at least 2 to 3 hours to ensure infection by the pathogen.
White Rust ranges worldwide and is able to survive varying weather conditions due to its production of multiple spore types.
http://web.aces.uiuc.edu/vista/pdf_pubs/960.PDF

Management

Controlling White Rust is very difficult due to the nature of the causal Albugo spp. pathogen. The method of control is tailored to specific crops and production systems. This is why identification of specific hosts (crops and possible weeds) is necessary to determine range and location of control methods.

Albugo spp. proliferate in wet and moist conditions so movement through infected fields should be limited after spore maturation in these conditions to limit spread. Minimizing irrigation in cool and moist seasons as well as eliminating windbreaks to allow faster leaf drying can be beneficial. When infection is recognized, systemically-infected plant material (including culled crops) should be completely removed and destroyed. Fields should be inspected every 7-14 days to remove additional material and monitor spread. On root crops, infected leaf removal either by mowing or plowing prior to harvest will limit the spread of the pathogen during harvest. Any susceptible plants or weeds should be mowed or eliminated to reduce spread.http://web.aces.uiuc.edu/vista/pdf_pubs/960.PDF

Both conventional and organic fungicides are available and should be used to limit spread and yield losses during the spring, early summer and fall on crops and susceptible neighboring plants. Each of the 17 specific races of the White Rust pathogen affects different plants so monitoring is essential as much as possible to limit overuse and cost of fungicide treatments. Common OMRI fungicides include sulphur, copper oxide, rosemary oil, and azadirachtin products. Labels and use can be found at http://attra.ncat.org/attra-pub/biorationals/. Common conventional fungicides include mefenoxam and fosetyl-aluminum products. Use and labels can be found at http://www.ipm.ucdavis.edu/PMG/r108101411.html

There are some resistant and partially-resistant varieties which are necessary in landscapes where White Rust is present. Long term White Rust persistence in fields is not an issue with all crops or in all states, however non-susceptible crop rotation in infected fields for at least three years is widely recommended to limit establishment and wider dispersal of this pathogen from plant debris, soil, and perennial root material. This pathogen can eliminate viable production of susceptible crops in specific fields indefinitely if infection is widespread over many years.http://web.aces.uiuc.edu/vista/pdf_pubs/960.PDF

Importance

White Rust can be a devastating disease on many important agricultural crops throughout the world. Seventeen races of white rust have been identified worldwide, each with a high level of host specificity. White Rust is an economically important foliar disease, causing substantial yield losses and eventual death of various crops. Yield losses of up to 20 percent have been recorded in canola fields, and white rust is considered the most important foliar disease of brassicacaes in Australia.
http://www.canola.okstate.edu/cropproduction/diseases/index.htm

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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