| Blumeria graminis | |
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| Genus: | Blumeria |
| Species: | B. graminis |
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| 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 (by its anamorph) Oidium monilioides or Oidium tritici.
Previously B. graminis was included within the genus Erysiphe , but molecular studies have placed it into a clade of its own. In 1975, it was moved to the new monospecific genus Blumeria. Blumeria differs from Erysiphe in its digitate haustoria and in details of the conidial wall. Blumeria is also considered to be phylogenetically distinct from Erisiphe as it solely infects the true grasses of Poaceae.
Eight special forms or formae speciales (ff.spp.) of B. graminis have been distinguished, each of which is parasitic on a particular genus or pareticular genera of grasses. Those that infect crop plants are B. g. f.sp. tritici , which causes powdery mildew of wheat and infects other grasses in the genera Triticum and Aegilops , f.sp. hordei on barley, f.sp. avenae on oats and f.sp. secalis on rye. Other formae speciales are pathogenic on wild grasses, including agropyri on grasses in the genera Agropyron and Elymus , bromi on Bromus spp., poae on Poa spp. and lolii on Lolium spp. (ryegrass).
The mycelium can cover the plant surface almost completely, especially the upper sides of leaves. Ascocarp is dark brown, globose with filamentous appendages, asci oblong. Ascospores hyaline, ellipsoid, 20–30 x 10–13 µm in size. Anamorph produces on hyaline conidiophores catenate conidia of oblong to cylindrical shape, not including fibrosin bodies, 32–44 x 12–15 µm in size. Haustoria are palmate.[ citation needed ]
B. graminis is unique among the Erysiphales by having conidia with a primary germ tube and finger-shaped ("digitate") appressoria. [1]
The genus name of Blumeria is in honour of Samuel Blumer (b. 1895), a Swiss botanist (Mycology), Phytopathology, from the University of Bern (Universität Bern). [2] [3]
The genus was circumscribed by Golovin[ who? ] ex Speer in Sydowia Vol.27 on page 2 in 1975.
B. graminis asexually produces conidia and sexually forms ascospores.
Conidia are mainly distributed by wind, pests, or human activities. The water initiating ascospores are hypothesized to be dispersed not only by wind but also by splashing water-droplets. [4]
It is biotrophic, and does not grow on synthetic media. Relatively cool and humid conditions are favourable for its growth. Its relatively great genetic variability enables it often to infect previously resistant plant varieties.[ citation needed ]
The genomes of B. g. f. sp. hordei [5] and B. g. f. sp. tritici have recently been sequenced. [6] Sequencing of the genome of the wheat powdery mildew B. g. f. sp. tritici, has allowed inference of important aspects of its evolution. It has been seen that it is the most repetitive fungal genome sequenced as of March 2013 [update] with 90% transposable elements. Additionally, 6540 genes were annotated, from which 437 encoded candidate secretor proteins and 165 for non-secreted candidate secretor proteins.[ clarification needed ] These were shown to be subject to positive selection, due to their implication in the gene-for-gene relationship to defeat plant disease resistance. The ability to infect tetraploid- as well as domesticated hexaploid wheat, was seen to be the result of mildew genomes being mosaics of ancient haplogroups that existed before wheat domestication.[ citation needed ] This has allowed wheat powdery mildew to maintain genetic flexibility, variability and thus a great potential for pathogen variation.[ citation needed ] It is hypothesized that this mosacisism can be maintained through clonal reproduction in populations with a small effective size or quasi-clonal reproduction in populations with large effective size.[ citation needed ]
Wheat powdery mildew is an obligate biotroph with a poorly understood evolutionary history. Sequencing its genome in 2013, many aspects of the evolution of its parasitism were unveiled. [7] Obligate biotrophy has appeared multiple times in evolution in both ascomycetes like B. graminis and basidiomycetes, thus different selective pressure must have acted in the different organisms through time.[ citation needed ] It has been seen that B. g. f.sp. tritici's genome is a mosaic of haplogroups with different divergence times, which explains its unique pathogen adaptability. Haplogroup Hold (diverged 40-80 mya) allows for the infection of wild tetraploid wheat and Hyoung (diverged 2-10 mya) allows for the infection of both domesticated hexaploid wheat species. Additionally, it has been seen that there is a positive selective pressure acting on genes that code for candidate secretor proteins and non-secreted candidate secretor proteins, indicating that these might participate in the gene-for-gene relationship of plant disease resistance.[ citation needed ]
Powdery mildew of wheat is relatively easy to diagnose [8] due to the characteristic little white spots of cotton-like mycelia. [9] These can appear on the upper and lower epidermis of the leaves. As the disease progresses they become a light tan color. [9] B. g. f. sp. tritici is an obligate parasite which means it only grows on living tissue. Though present throughout wheat growing regions, it especially favors the eastern seaboard of the United States as well as coastal regions of the United Kingdom.[ citation needed ]
Triticum spp. (wheat) is the only host of B. g. f. sp. tritici. [8] Signs on the foliage of wheat are white, powdery mycelium and conidia. [10] As the disease progresses, the patches turn gray and small dark black or brown cleistothecia form in the mycelium mass. [11] Symptoms progress from lower to upper leaves. Symptoms of powdery mildew are chlorotic areas surrounding the infected areas. [10] The lower leaf surface corresponding to the mycelial mat will also show chlorosis. [11] Lower leaves are commonly the most infected because of higher humidity around them. [8]
B. g. f. sp. tritici has a polycyclic life cycle typical of its phylum, Ascomycota. Powdery mildew of wheat overwinters as cleistothecia dormant in plant debris. Under warmer conditions, however, the fungus can overwinter as asexual conidia or mycelium on living host plants. It can persist between seasons most likely as ascospores in wheat debris left in the field. Ascospores are sexual spores produced from the cleistothecia. These spores, as well as conidia, serve as the primary inoculum and are dispersed by wind. Neither spore requires free water to germinate, only high relative humidity. [11] Wheat powdery mildew thrives in cool humid conditions and cloudy weather increases chances of disease. When conidia land on a wheat leaf's hydrophobic surface cuticle, they release proteins which facilitate active transport of lightweight anions between leaf and fungus even before germination. This process helps Blumeria recognize that it is on the correct host and directs growth of the germ tube. [12] Both ascospores and conidia germinate directly with a germ tube. Conidia can recognize the host plant and within one minute of initial contact, the direction of germ tube growth is determined. The development of appressoria then begins infection following the growth of a germ tube. [13] After initial infection, the fungus produces haustoria inside of the wheat cells and mycelium grows on the plant's outer surface. [11] Powdery mildew of wheat produces conidia during the growing season as often as every 7 to 10 days. [14] These conidia function as secondary inoculum as growth and reproduction repeat throughout the growing season.
Powdery mildew of wheat thrives in cool, humid climates and proliferates in cloudy weather conditions. [15] The pathogen can also be an issue in drier climates if wheat fields are irrigated. [16] Ideal temperatures for growth and reproduction of the pathogen are between 60 °F (16 °C) and 70 °F (21 °C) with growth ceasing above 77 °F (25 °C). Dense, genetically similar plantings provide opportune conditions for growth of powdery mildew. [11]
Controlling the disease involves eliminating conducive conditions as much as possible by altering planting density and carefully timing applications and rates of nitrogen. Since nitrogen fertilizers encourage dense leafy growth, nitrogen should be applied at precise rates, less than 70 pounds per acre, to control decrease severity. Crop rotation with non-host plants is another way to keep mildew infection to a minimum, however the aerial nature of conidia and ascospore dispersal makes it of limited use. Wheat powdery mildew can also be controlled by eliminating the presence of volunteer wheat in agricultural fields as well as tilling under crop residues. [14]
Chemical control is possible with fungicides such as triadimefon and propiconazole. Another chemical treatment involves treating wheat with a silicon solution or calcium silicate slag. Silicon helps the plant cells defend against fungal attack by degrading haustoria and by producing callose and papilla. With silicon treatment, epidermal cells are less susceptible to powdery mildew of wheat. [17]
Milk has long been popular with home gardeners and small-scale organic growers as a treatment for powdery mildew. Milk is diluted with water (typically 1:10) and sprayed on susceptible plants at the first sign of infection, or as a preventative measure, with repeated weekly application often controlling or eliminating the disease. Studies have shown milk's effectiveness as comparable to some conventional fungicides, [18] and better than benomyl and fenarimol at higher concentrations. [19] Milk has proven effective in treating powdery mildew of summer squash, [19] pumpkins, [18] grapes, [20] and roses. [20] The exact mechanism of action is unknown, but one known effect is that ferroglobulin, a protein in whey, produces oxygen radicals when exposed to sunlight, and contact with these radicals is damaging to the fungus. [20]
Another way to control wheat powdery mildew is breeding in genetic resistance, using "R genes" (resistance genes) to prevent infection. There are at least 25 loci on the wheat genome that encode resistance to powdery mildew. If the particular variety of wheat has only one loci for resistance, the pathogen may be controlled only for a couple years. If, however, the variety of wheat has multiple loci for resistance, the crop may be protected for around 15 years. Because finding these loci can be difficult and time-consuming, molecular markers are used to facilitate combining resistant genomes. [15] One organization working towards identifying these molecular markers is the Coordinated Agricultural Project for Wheat . With these markers established, researchers will then be able to determine the most effective combination of resistance genes. [21]
HSP70-4 is an HSP70 – a family of heat shock proteins – in Arabidopsis . [22] The ortholog HvHSP70-4 in barley (Hordeum vulgare) is disclosed by Molitor et al., 2011. [22] They find that it is transcribed in response to B. graminis infection, is protective against Bg infection, and that prophylactic infection with Piriformospora indica produces systemic induced resistsance to Bg. [22]
Powdery mildew can be found in all wheat growing areas of the United States but usually will be most severe in the east and southeast. [11] It is more common in areas with a humid or semi-arid environment where wheat is grown. [11] Powdery mildew has become a more important disease in some areas because of increased application of nitrogen fertilizer, which favors the development of the fungus. [10] Severe symptoms of powdery mildew can cause stunting of wheat. [10] If unmanaged, this disease can reduce yields significantly by reducing photosynthetic areas and causes non-seed producing tillers. [8] Powdery mildew causes reduced kernel size and lower yields. [14] The sooner powdery mildew begins to develop and how high on the plant it develops by flowering the larger the yield loss. [14] Yield Losses up to 45 percent have been shown in Ohio on susceptible varieties when plants are infected early and weather favors disease. [14]
Rusts are fungal plant pathogens of the order Pucciniales causing plant fungal diseases.
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 its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
Uncinula necator is a fungus that causes powdery mildew of grape. It is a common pathogen of Vitis species, including the wine grape, Vitis vinifera. The fungus is believed to have originated in North America. European varieties of Vitis vinifera are more or less susceptible to this fungus. Uncinula necator infects all green tissue on the grapevine, including leaves and young berries. It can cause crop loss and poor wine quality if untreated. The sexual stage of this pathogen requires free moisture to release ascospores from its cleistothecia in the spring. However, free moisture is not needed for secondary spread via conidia; high atmospheric humidity is sufficient. Its anamorph is called Oidium tuckeri.
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.
Erysiphales are an order of ascomycete fungi. The order contains one family, Erysiphaceae. Many of them cause plant diseases called powdery mildew.
This is a glossary of some of the terms used in phytopathology.
Powdery mildew is a fungal disease of barley caused by Blumeria graminis f. sp. hordei. The disease has a worldwide distribution and is most damaging in cool, wet climates. The host range of the form species hordei is restricted to barley and other Hordeum species.
Erysiphe cruciferarum is a plant pathogen of the family Erysiphaceae, which causes the main powdery mildew of crucifers, including on Brassica crops, such as cauliflower, cabbage, broccoli, and Brussels sprouts. E. cruciferarum is distributed worldwide, and is of particular concentration in continental Europe and the Indian subcontinent. E. cruciferarum is an ascomycete fungus that has both sexual and asexual stages. It is also an obligate parasite that appears to have host specificity; for example, isolates from turnip will not infect Brussels sprout, and vice versa. While being a part of the family Erysiphaceae, it belongs to those members in which the conidia are formed singly and whose haustoria are multilobed.
Erysiphe betae is a fungal plant pathogen. It is a form of powdery mildew that can affect crops of sugar beet, that could cause up to a 30% yield loss. The fungus occurs worldwide in all regions where sugar beet is grown and it also infects other edible crops, e.g. beetroot.
Pyrenophora tritici-repentis (teleomorph) and Drechslera tritici-repentis (anamorph) is a necrotrophic plant pathogen of fungal origin, phylum Ascomycota. The pathogen causes a disease originally named yellow spot but now commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis. At least eight races of the pathogen are known to occur based on their virulence on a wheat differential set.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Podosphaera leucotricha is a plant pathogen that can cause powdery mildew of apples and pears.
Brasiliomyces malachrae is a species of fungus in the family Erysiphaceae. It is a plant pathogen that grows on Gossypium, Lavatera assurgentiflora, Malachra capitata, Malvastrum coromandelianum, and species of Malvaceae. It is found in South America.
Podosphaera macularis is a plant pathogen infecting several hosts including chamomile, caneberrie, strawberries, hop, hemp and Cineraria. It causes powdery mildew of hops.
Erysiphe heraclei is a plant pathogen that causes powdery mildew on several species including dill, carrot and parsley.
Oidium mangiferae is a plant pathogen that infects mango trees causing powdery mildew. Powdery mildew of mango is an Ascomycete pathogen of the Erysiphales family that was initially described by Berthet in 1914, using samples collected from Brazil. O. mangiferae is found in all areas where mangoes have been raised long term, but is particularly widespread in India where both the host and the pathogen are native. Currently no teleomorph stage has been identified, but due to certain morphological characteristics it has been suggested that O. mangiferae belongs in the Erysiphe polygony group. Mango is the only known host for this pathogen, though O. mangiferae appears to be identical to fungi responsible for powdery mildew diseases on various other plant species, particularly oak, though some differences may be observed. In particular, the number of cells in conidiophores varies from 2 on mango to 3-5 on oak. O. mangiferae has been known to infect oak leaves in the laboratory, however due to the lack of a known teleomorph stage O. mangiferae is still considered to only be a pathogen of mango. Recent analysis of its ribosomal DNA suggests it is conspecific with Erysiphe alphitoides, the causative agent of powdery mildew in European oaks.
Podosphaera fuliginea is a plant pathogen that causes powdery mildew on cucurbits. Podosphaera fuliginea and Erysiphe cichoracearum are the two most commonly recorded fungi causing cucurbit powdery mildew. In the past, Erysiphe cichoracearum was considered to be the primary causal organism throughout most of the world. Today, Podosphaera fuliginea is more commonly reported.
Erysiphe graminis f.sp. tritici is a plant pathogen that causes a fungal infection known as powdery mildew. It is most common in grains, and it can be identified by the characteristic white spots on leaves and stems that appear to be made of powder. Powdery mildew is one of the most widespread and easily recognizable plant diseases.
Alternaria brassicicola is a fungal necrotrophic plant pathogen that causes black spot disease on a wide range of hosts, particularly in the genus of Brassica, including a number of economically important crops such as cabbage, Chinese cabbage, cauliflower, oilseeds, broccoli and canola. Although mainly known as a significant plant pathogen, it also contributes to various respiratory allergic conditions such as asthma and rhinoconjunctivitis. Despite the presence of mating genes, no sexual reproductive stage has been reported for this fungus. In terms of geography, it is most likely to be found in tropical and sub-tropical regions, but also in places with high rain and humidity such as Poland. It has also been found in Taiwan and Israel. Its main mode of propagation is vegetative. The resulting conidia reside in the soil, air and water. These spores are extremely resilient and can overwinter on crop debris and overwintering herbaceous plants.
Golovinomyces orontii is a species of fungus that causes powdery mildew disease and it is in the family Erysiphaceae. It is an obligate biotroph that infects plants in several families including Acanthaceae, Asteraceae, Brassicaceae, Cucurbitaceae, and Lamiaceae.