Blumeria graminis

Source: Wikipedia, the free encyclopedia.

Blumeria graminis
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Leotiomycetes
Order:
Erysiphales
Family:
Erysiphaceae
Genus:
Blumeria
Species:
B. graminis
Binomial name
Blumeria graminis

Blumeria graminis (commonly called barley powdery mildew or corn mildew) is a fungus that causes

anamorph
) Oidium monilioides or Oidium tritici.

Systematics

Previously B. graminis was included within the genus

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

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).

Morphology

The

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

appressoria.[1]

Taxonomy

The genus name of Blumeria is in honour of

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.

Ecology

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]

Genetics and Evolution

Genetics

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 with 90%

positive selection, due to their implication in the gene-for-gene relationship to defeat plant disease resistance
. The ability to infect
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
]

Evolution of Blumeria graminis f.sp. tritici

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.

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]

Pathology

Powdery mildew of wheat is relatively easy to diagnose

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
]

Hosts and symptoms

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]

Disease cycle

B. g. f. sp. tritici has a polycyclic life cycle typical of its phylum,

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.

Environment

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]

Management

Controlling the disease involves eliminating conducive conditions as much as possible by altering planting density and carefully timing applications and rates of

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

haustoria and by producing callose and papilla. With silicon treatment, epidermal cells are less susceptible to powdery mildew of wheat.[17]

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

Piriformospora indica produces systemic induced resistsance to Bg.[22]


Importance

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]

References

  1. PMID 18680422
    .
  2. S2CID 246307410
    . Retrieved January 27, 2022.
  3. ^ Who's who in Switzerland Including the Principality of Liechtenstein. International Publications Service. 1981
  4. PMID 28705398
    .
  5. S2CID 19651350
    .
  6. ^ This review... Lo, Libera; Lanver, Daniel; Schweizer, Gabriel; Tanaka, Shigeyuki; Liang, Liang; Tollot, Marie; Zuccaro, Alga; Reissmann, Stefanie; Kahmann, Regine (2015). "Fungal Effectors and Plant Susceptibility".
    S2CID 39714412
    .     ...cites this study: Wicker, Thomas; Simone Oberhaensli; Francis Parlange; Jan P. Buchmann; Margarita Shatalina; Stefan Roffler; Roi Ben-David; Jaroslav Doležel; Hana Šimková; Paul Schulze-Lefert; Pietro D. Spanu; Rémy Bruggmann; Joelle Amselem; Hadi Quesneville; Emiel Ver Loren van Themaat; Timothy Paape; Kentaro K. Shimizu; Beat Keller (2013). "The wheat powdery mildew genome shows the unique evolution of an obligate biotroph". Letters.
    S2CID 5648330
    .
  7. S2CID 5648330
    .
  8. ^ a b c d Maloy, Otis C.; Inglis, Debra Ann (1993). "Powdery Mildew". Washington State University. Archived from the original on 23 December 2002.
  9. ^ a b Stromberg, Erik. "Wheat Powdery Mildew". Department of Plant Pathology, Physiology and Weed Science. Virginia Tech. Archived from the original on 7 May 2012.
  10. ^ a b c d Wegulo, Stephen N. (February 2010). "Powdery Mildew of Wheat". University of Nebraska–Lincoln Extension. Archived from the original on 15 April 2012. Retrieved 1 June 2014.
  11. ^
    University of Nebraska-Lincoln Department of Plant Pathology. Retrieved from University of Nebraska–Lincoln. "Powdery Mildew of Wheat Key words: Plant Disease, Wheat, Triticum, Blumeria graminis f. Sp. Tritici, Erysiphe graminis f. Sp. Tritici, Oidium monilioides". Archived from the original
    on 2012-08-19. Retrieved 2014-06-01..
  12. doi:10.1006/pmpp.1999.0241
    .
  13. doi:10.1006/pmpp.2000.0304
    .
  14. ^ a b c d e Lipps, Patrick E. (n.d). "Powdery Mildew of Wheat," The Ohio State University Extension. Retrieved from http://ohioline.osu.edu/ac-fact/0010.htmltm.
  15. ^
    S2CID 20354017
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  16. doi:10.1111/j.1365-3059.1984.tb01324.x
    .
  17. Phytopathology, 93. American Phytopathological Society. Retrieved from http://www.siliforce.com/pdf/7c/Belanger-%20%20evedence%20silicon%20powdery%20mildew%20on%20wheat.pdf Archived 2016-03-04 at the Wayback Machine
    .
  18. ^ a b DeBacco, Matthew. "Compost Tea and Milk to Suppress Powdery Mildew (Podosphaera xanthii) on Pumpkins and Evaluation of Horticultural Pots Made from Recyclable Fibers Under Field Conditions". University of Connecticut. Retrieved 5 May 2013.
  19. ^
    doi:10.1016/s0261-2194(99)00046-0
    .
  20. ^ a b c Raloff, Janet. "A Dairy Solution to Mildew Woes". Science News Magazine. Retrieved 5 May 2013.
  21. University of California-Davis. Archived from the original
    (PDF) on 2013-05-17.
  22. ^
    PMID 35022724
    .
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