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Thursday 27 June 2019

Fusarium graminearum

Gibberella zeae

Fusarium graminearum)
Gibberella zeae
F.graminearum.JPG
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Sordariomycetes
Order:
Hypocreales
Family:
Nectriaceae
Genus:
Gibberella
Species:
G. zeae
Binomial name
Gibberella zeae
(Schwein.) Petch, (1936)
Synonyms
Botryosphaeria saubinetii
Dichomera saubinetii
Dothidea zeae
Fusarium graminearum
Fusarium roseum
Gibbera saubinetii
Gibberella roseum
Gibberella saubinetii
Sphaeria saubinetii
Sphaeria zeae
Gibberella zeae, also known by the name of its anamorph Fusarium graminearum, is a plant pathogen which causes fusarium head blight, a devastating disease on wheat and barley.[1] The pathogen is responsible for billions of dollars in economic losses worldwide each year.[2] Infection causes shifts in the amino acid composition of wheat,[3] resulting in shriveled kernels and contaminating the remaining grain with mycotoxins, mainly deoxynivalenol, which inhibits protein biosynthesis; and zearalenone, an estrogenic mycotoxin. These toxins cause vomiting, liver damage, and reproductive defects in livestock, and are harmful to humans through contaminated food. Despite great efforts to find resistance genes against F. graminearum, no completely resistant variety is currently available. Research on the biology of F. graminearum is directed towards gaining insight into more details about the infection process and reveal weak spots in the life cycle of this pathogen to develop fungicides that can protect wheat from scab infection.

Life cycle[edit]

F. graminearum is a haploid homothallic ascomycete. The fruiting bodies, perithecia, develop on the mycelium and give rise to ascospores, which land on susceptible parts of the host plant to germinate. The fungus causes fusarium head blight on wheat, barley, and other grass species, as well as ear rot on corn. The primary inocula are the ascospores, sexual spores which are produced in the perithecia.[4] Spores are forcibly discharged and can germinate within six hours upon landing on the plant surface. The scab disease is monocyclic; after one cycle of infection with ascospores, the fungus produces macroconidia by asexual reproduction.[5] These structures overwinter in the soil or in plant debris on the field and give rise to the mycelium in the next season.

Host and symptoms[edit]

The pathogen is capable of causing a variety of diseases: head blight or 'scab' on wheat (Triticum), barley (Hordeum), rice (Oryza), oats (Avena), and Gibberella stalk and ear rot disease on maize (Zea). Additionally, the fungus may infect other plant species without causing any disease symptoms.[6]
Maize
In Gibberella stalk rot, the leaves on early-infected plants will turn a dull greyish-green, and the lower internodes will soften and turn a tan to dark-brown. A pink-red discoloration occurs within the stalks of diseased tissue. Shredding of the pith may reveal small, round, black perithecia on the stalks.[7] Gibberella (red) ear rot can have a reddish mold that is often at the ear tip. The infection occurs by colonizing corn silk and symptoms first occur at the ear's apex. The white mycelium turns from pink to red over time, eventually covering the entire ear. Ears that become infected early don't fully develop the reddish mold near the ear tip, as the mold grows between the husks and ear.[6]
Rice
Gibberella zeae can turn affected seeds red and cause brown discoloration in certain areas on the seed or the entire seed surface. The surface of husks develop white spots that later become yellow and salmon or carmine. Infected grains are light, shrunken and brittle. Stem nodes begin to rot and wilt, eventually causing them to turn black and disintegrate when they are infected by the fungal pathogen.[7]
Wheat
Brown, dark purple-black necrotic lesions will form on the outer surface of the spikelets, what the wheat ear breaks up into. The lesions may be referred to as scabs, but this is not to be confused and associated with other scab diseases such as those with different host and pathogen. Head blight is visible before the spikes mature.[7] Spikelets begin to appear water-soaked before the loss of chlorophyll, which gives a white straw color. Peduncles that are directly under the inflorescence can become discolored into a brown-purple color. Tissues of the inflorescence typically become blighted into a bleached tan appearance, and the grain within it atrophies.[6] The awn will become deformed, twisted and curve in a downward direction.
Barley
Infections on barley are not always visible in the field. Similar to wheat, infected spikelets show a browning or water-soaked appearance. The infected kernels display a tan to dark brown discoloration. During long periods of wetness, pink to salmon-orange spore masses can be seen on the infected spikelets and kernels.[6] The cortical lesions of infected seeds become a reddish-brown in cool, moist soil. Warm soil can cause head blight to occur after emergence, and crown and basal culm rot can be observed in later plant development.[7]

Infection process[edit]

Wheat scab caused by G. zeae (artificial inoculation)
F. graminearum infects wheat spikes from anthesis through the soft dough stage of kernel development. The fungus enters the plant mostly through the flowers; however, the infection process is complex and the complete course of colonization of the host has not been described. Germ tubes seem not to be able to penetrate the hard, waxy surface of the lemma and palea which protect the flower. The fungus enters the plant through natural openings such as stomates, and needs soft tissue such as the flowers, anthers and embryo to infect the plant.[8] From the infected floret, the fungus can grow through the rachis and cause severe damage in a short period of time under favorable conditions. Upon germination of the spores on the anthers and the surface of the developing kernel, hyphae penetrate the epicarp and spread through the seed coat. Successively, the different layers of the seed coat and finally the endosperm are colonized and killed.[9]

Management[edit]

The control of this disease can be achieved using a combination of the following strategies: fungicide applications, resistance breeding, proper storage, crop rotation, crop residue tillage, and seed treatment. The correct usage of fungicide applications against Fusarium head blight can reduce the disease by 50 to 60 percent.[10] Fusarium refers to a large genus of soil fungi that are economically important due to the profound effects they have on crops. Application of fungicides is necessary at early heading date for barley and early flowering for wheat, where the early application can limit the infection of the ear. Barley and wheat differ in fungicide application because of their differences in developmental traits.[11] The disease generally develops late in the season or during storage, so fungicide use is only effective in the early season. Management against insect pests such as ear borers, for corn, will also reduce the infection of the ear from wounds caused by insect feeding.[12]
Cultivating a variety of hosts that are resistant to Fusarium head blight is one of the most evidence-based and cost-effective ways to manage the disease. Using varieties that have looser tusks that cover the ear are less vulnerable to Fusarium head blight. Once the crop has been harvested, it is essential to store it at low moisture, below 15%, as this will reduce the appearance of Gibberella zeae and Fusarium species in storage.[12]
Avoiding the planting of small grain crops following other small grain crops or corn and tillage of crop residue minimizes the chances of Fusarium head blight in environmentally favorable years. The rotation of small grains with soybean or other non-host crops has proven to reduce Fusarium head blight and mycotoxin contamination.[10] Crop rotation with the tillage of residue prevents crops from remaining to infect on the soil surface. Residues can provide an overwintering medium for Fusarium species to cause Fusarium head blight. As a result, the chances of infection are greatly improved in the succeeding small grain crop.[10] If minimal or no tillage occurs, the residue spreads and allows the fungus to overwinter on stalks and rotted ears of corn and produce spores.
The seeds (kernels) that colonize with the fungus have less resistance because of poor germination. Planting certified or treated seeds can reduce the amount of seedling blight, which is caused by the seeds colonized with the fungus. If it is necessary to replant seeds that were harvested from a Fusarium head blight infected field, then the seeds should be treated to avoid reoccurrence of the infection.[10]

Importance[edit]

The loss of yield and contamination of seed with mycotoxins, alongside reduced seed quality, are the main contributions to the impact of this disease. Two mycotoxins, trichothecene deoxynivalenol, a strong biosynthesis inhibitor, and zearalenone, an estrogenic mycotoxin, can be found in grains after Fusarium head blight epidemics.[13] Deoxynivalenol is a type of vomitoxin and, as its name states, is an antifeedant. Livestock that consume crops contaminated with vomitoxin become sick and refuse to eat anymore. Zearalenone is a phytoestrogen, mimicking mammals' estrogen. It can be disastrous if it gets into the food chain, as zearalenone causes abortions in pregnant females and feminization of males.[14]
In 1982, a major epidemic affected 4 million hectares of the spring wheat and barely growing in the northern Great Plains of North Dakota, South Dakota, and Minnesota. The yield losses exceeded 6.5 million tons worth approximately $826 million, with total losses related to the epidemic near one billion dollars.[7] Years that followed this epidemic, reported losses that have been estimated between $200-$400 million annually. Losses in barley because of Fusarium head blight are large in part due to the presence of deoxynivalenol. Barley prices from 1996 in Minnesota fell from $3.00 to $2.75 per bushel if the mycotoxin was present and another $0.05 for each part per million of deoxynivalenol present.[7]

See also[edit]

References[edit]

  1. ^ Bai G, Shaner G (2004):Management and resistance in wheat and barley to Fusarium head blight. Annual Review of Phytopathology 42: 135-161 [1]
  2. ^ De Wolf ED, Madden LV, Lipps PE (2003): Risk assessment models for wheat Fusarium head blight epidemics based on within-season weather data. Phytopathology 93: 428-435. [2]
  3. ^ Beyer M, Aumann J (2008): Effects of Fusarium infection on the amino acid composition of winter wheat grain. Food Chemistry 111: 750-754. [3]
  4. ^ Beyer M, Verreet J-A (2005): Germination of Gibberella zeae ascospores as affected by age of spores after discharge and environmental factors. European Journal of Plant Pathology 111: 381-389. [4]
  5. ^ Beyer M, Röding S, Ludewig A, Verreet J-A (2004): Germination and survival of Fusarium graminearum macroconidia as affected by environmental factors. Journal of Phytopathology 152: 92-97.[5]
  6. ^ Jump up to: a b c d Rubella, Goswami; Kistler, Corby (2004). "Heading for disaster: Fusarium graminearum on cereal crop" (PDF). Molecular Plant Pathology. 5 (6): 515–525. doi:10.1111/J.1364-3703.2004.00252.X. PMID 20565626.
  7. ^ Jump up to: a b c d e f "headblight of maize (Gibberella zeae)". www.plantwise.org. Retrieved 2017-10-25.
  8. ^ Bushnell WR, Leonard KJ (2003): Fusarium head blight of wheat and barley.APS Press, St. Paul, Minnesota
  9. ^ Jansen C, Von Wettstein D, Schäfer W, Kogel K-H, Felk A, Maier FJ (2005): Infection patterns in barley and wheat spikes inoculated with wild-type and trichodiene synthase gene disrupted Fusarium graminearum. Proceedings of the National Academy of Sciences 102: 16892-16897 [6]
  10. ^ Jump up to: a b c d "Managing Fusarium Head Blight in Virginia Small Grains". Retrieved 2017-10-25.
  11. ^ Alqudah, Ahmad M.; Schnurbusch, Thorsten (2017-05-30). "Heading Date Is Not Flowering Time in Spring Barley". Frontiers in Plant Science. 8: 896. doi:10.3389/fpls.2017.00896. ISSN 1664-462X. PMC 5447769. PMID 28611811.
  12. ^ Jump up to: a b User, Super. "Fusarium and gibberella ear rot (extended information)". maizedoctor.org. Retrieved 2017-10-25.
  13. ^ Guenther, John C.; Trail, Frances (2005). "The Development and Differentiation of Gibberella zeae (Anamorph: Fusarium graminearum) during Colonization of Wheat". Mycologia. 97 (1): 229–237. doi:10.1080/15572536.2006.11832856. JSTOR 3762213.
  14. ^ Volk, Tom. "Gibberella zeae or Fusarium graminearum, head blight of wheat". botit.botany.wisc.edu. Retrieved 2017-10-25.

External links[edit]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Gibberella_zeae&oldid=895500975"
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Physarum polycephalum

Physarum polycephalum

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Physarum polycephalum
Physarum polycephalum plasmodium.jpg
Physarum polycephalum plasmodium forming over tree chunk.
Scientific classification
Kingdom:
Protista
Phylum:
Mycetozoa
Class:
Myxogastria
Order:
Physarales
Family:
Physaraceae
Genus:
Physarum
Species:
P. polycephalum
Binomial name
Physarum polycephalum
Physarum polycephalum, literally the "many-headed slime", is a slime mold that inhabits shady, cool, moist areas, such as decaying leaves and logs. Like slime molds in general, it is sensitive to light; in particular, light can repel the slime mold and be a factor in triggering spore growth.

Characteristics[edit]

This protist may be seen without a microscope. P. polycephalum is typically yellow in color, and eats fungal spores, bacteria, and other microbes. P. polycephalum is one of the easiest eukaryotic microbes to grow in culture, and has been used as a model organism for many studies involving amoeboid movement and cell motility.[1]

Life cycle[edit]

The main vegetative phase of P. polycephalum is the plasmodium (the active, streaming form of slime molds). The plasmodium consists of networks of protoplasmic veins, and many nuclei. It is during this stage that the organism searches for food.[2] The plasmodium surrounds its food and secretes enzymes to digest it.
If environmental conditions cause the plasmodium to desiccate during feeding or migration, Physarum will form a sclerotium. The sclerotium is basically hardened multinucleated tissue that serves as a dormant stage, protecting Physarum for long periods of time. Once favorable conditions resume, the plasmodium reappears to continue its quest for food.
As the food supply runs out, the plasmodium stops feeding and begins its reproductive phase. Stalks of sporangia form from the plasmodium; it is within these structures that meiosis occurs and spores are formed. Sporangia are usually formed in the open so that the spores they release will be spread by wind currents.
Spores can remain dormant for years if need be. However, when environmental conditions are favorable for growth, the spores germinate and release either flagellated or amoeboid swarm cells (motile stage); the swarm cells then fuse together to form a new plasmodium.

Streaming behavior[edit]

The movement of P. polycephalum is termed shuttle streaming. Shuttle streaming is characterized by the rhythmic back-and-forth flow of the protoplasm; the time interval is approximately two minutes. The forces of the streaming vary for each type of microplasmodium.
The force in amoeboid microplasmodia is generated by contraction and relaxation of a membranous layer probably consisting of actin (type of filament associated with contraction). The filament layer creates a pressure gradient, over which the protoplasm flows within limits of the cell periphery.
The force behind streaming in the dumbbell-shaped microplasmodia is generated by volume changes in both the periphery of the cell and in the invagination system of the cell membrane.

Situational behavior[edit]

P. polycephalum plasmodium cultivating two "islands" of agar substrate overlying a glass coverslip.
Physarum polycephalum has been shown to exhibit characteristics similar to those seen in single-celled creatures and eusocial insects. For example, a team of Japanese and Hungarian researchers have shown P. polycephalum can solve the Shortest path problem. When grown in a maze with oatmeal at two spots, P. polycephalum retracts from everywhere in the maze, except the shortest route connecting the two food sources.[3] When presented with more than two food sources, P. polycephalum apparently solves a more complicated transportation problem. With more than two sources, the amoeba also produces efficient networks.[4] In a 2010 paper, oatflakes were dispersed to represent Tokyo and 36 surrounding towns.[5][6] P. polycephalum created a network similar to the existing train system, and "with comparable efficiency, fault tolerance, and cost". Similar results have been shown based on road networks in the United Kingdom[7] and the Iberian peninsula (i.e., Spain and Portugal).[8] Some researchers claim that P. polycephalum is even able to solve the NP-hard Steiner minimum tree problem.[9]
P. polycephalum can not only solve these computational problems, but also exhibits some form of memory. By repeatedly making the test environment of a specimen of P. polycephalum cold and dry for 60-minute intervals, Hokkaido University biophysicists discovered that the slime mould appears to anticipate the pattern by reacting to the conditions when they did not repeat the conditions for the next interval. Upon repeating the conditions, it would react to expect the 60-minute intervals, as well as testing with 30- and 90-minute intervals.[10][11]
P. polycephalum has also been shown to dynamically re-allocate to apparently maintain constant levels of different nutrients simultaneously.[12][13] In particular, specimen placed at the center of a Petri dish spatially re-allocated over combinations of food sources that each had different protein–carbohydrate ratios. After 60 hours, the slime mould area over each food source was measured. For each specimen, the results were consistent with the hypothesis that the amoeba would balance total protein and carbohydrate intake to reach particular levels that were invariant to the actual ratios presented to the slime mould.
As the slime mould does not have any nervous system that could explain these intelligent behaviours, there has been considerable interdisciplinary interest in understanding the rules that govern its behaviour. Scientists are trying to model the slime mold using a number of simple, distributed rules. For example, P. polycephalum has been modeled as a set of differential equations inspired by electrical networks. This model can be shown to be able to compute shortest paths.[14] A very similar model can be shown to solve the Steiner tree problem.[9] However, currently these models do not make sense biologically, as they for example assume energy conservation inside the slime mould. Living organisms consume food, so energy can not be conserved. To build more realistic models, more data about the slime mould's network construction needs to be gathered. To this end, researchers are analysing the network structure of lab-grown P. polycephalum.[15]
In a book[16] and several preprints that have not been scientifically peer reviewed,[17][18] it has been claimed that because plasmodia appear to react in a consistent way to stimuli, they are the "ideal substrate for future and emerging bio-computing devices".[18] An outline has been presented showing how it may be possible to precisely point, steer and cleave plasmodium using light and food sources,[18] especially Valerian root.[19] Moreover, it has been reported that plasmodia can be made to form logic gates,[17] enabling the construction of biological computers. In particular, plasmodia placed at entrances to special geometrically shaped mazes would emerge at exits of the maze that were consistent with truth tables for certain primitive logic connectives. However, as these constructions are based on theoretical models of the slime mould, in practice these results do not scale to allow for actual computation. When the primitive logic gates are connected to form more complex functions, the plasmodium ceased to produce results consistent with the expected truth tables.
Even though complex computations using Physarum as a substrate are currently not possible, researchers have successfully used the organism's reaction to its environment in a USB sensor[20] and to control a robot.[21]

References[edit]

Specific
  1. ^ "- Journal of Physics D: Applied Physics - IOPscience". iopscience.iop.org. Retrieved 2017-06-08.
  2. ^ "Life at the Edge of Sight — Scott Chimileski, Roberto Kolter | Harvard University Press". www.hup.harvard.edu. Retrieved 2018-01-26.
  3. ^ Nakagaki, Toshiyuki; Yamada, Hiroyasu; Tóth, Ágota (2000). "Intelligence: Maze-solving by an amoeboid organism". Nature. 407 (6803): 470. doi:10.1038/35035159. PMID 11028990.
  4. ^ Nakagaki, Toshiyuki; Kobayashi, Ryo; Nishiura, Yasumasa; Ueda, Tetsuo (November 2004). "Obtaining multiple separate food sources: behavioural intelligence in Physarum plasmodium". Proceedings of the Royal Society B. 271 (1554): 2305–2310. doi:10.1098/rspb.2004.2856. PMC 1691859. PMID 15539357.
  5. ^ Tero, Atsushi; Takagi, Seiji; Saigusa, Tetsu; Ito, Kentaro; Bebber, Dan P.; Fricker, Mark D.; Yumiki, Kenji; Kobayashi, Ryo; Nakagaki, Toshiyuki (January 2010). "Rules for Biologically Inspired Adaptive Network Design". Science. 327 (5964): 439–442. Bibcode:2010Sci...327..439T. CiteSeerX 10.1.1.225.9609. doi:10.1126/science.1177894. PMID 20093467.
  6. ^ Moseman, Andrew (2010-01-22). "Brainless Slime Mold Builds a Replica Tokyo Subway". Discover Magazine. Retrieved 2011-06-22.
  7. ^ Adamatzky, Andrew; Jones, Jeff (2010). "Road planning with slime mould: If Physarum built motorways it would route M6/M74 through Newcastle". International Journal of Bifurcation and Chaos. 20 (10): 3065–3084. arXiv:0912.3967. Bibcode:2010IJBC...20.3065A. doi:10.1142/S0218127410027568.
  8. ^ Adamatzky, Andrew; Alonso-Sanz, Ramon (July 2011). "Rebuilding Iberian motorways with slime mould". Biosystems. 5 (1): 89–100. doi:10.1016/j.biosystems.2011.03.007. PMID 21530610.
  9. ^ Jump up to: a b Caleffi, Marcello; Akyildiz, Ian F.; Paura, Luigi (2015). "On the Solution of the Steiner Tree NP-Hard Problem via Physarum BioNetwork". IEEE/ACM Transactions on Networking. PP (99): 1092–1106. doi:10.1109/TNET.2014.2317911.
  10. ^ Saigusa, Tetsu; Tero, Atsushi; Nakagaki, Toshiyuki; Kuramoto, Yoshiki (2008). "Amoebae Anticipate Periodic Events". Physical Review Letters. 100 (1): 018101. Bibcode:2008PhRvL.100a8101S. doi:10.1103/PhysRevLett.100.018101. PMID 18232821.
  11. ^ Barone, Jennifer (2008-12-09). "Top 100 Stories of 2008 #71: Slime Molds Show Surprising Degree of Intelligence". Discover Magazine. Retrieved 2011-06-22.
  12. ^ Dussutour, Audrey; Latty, Tanya; Beekman, Madeleine; Simpson, Stephen J. (2010). "Amoeboid organism solves complex nutritional challenges". PNAS. 107 (10): 4607–4611. Bibcode:2010PNAS..107.4607D. doi:10.1073/pnas.0912198107. PMC 2842061. PMID 20142479.
  13. ^ Bonner, John Tyler (2010). "Brainless behavior: A myxomycete chooses a balanced diet". PNAS. 107 (12): 5267–5268. Bibcode:2010PNAS..107.5267B. doi:10.1073/pnas.1000861107. PMC 2851763. PMID 20332217.
  14. ^ Becchetti, Luca; Bonifaci, Vincenzo; Dirnberger, Michael; Karrenbauer, Andreas; Mehlhorn, Kurt (2013). Physarum Can Compute Shortest Paths: Convergence Proofs and Complexity Bounds. ICALP. Lecture Notes in Computer Science. 7966. pp. 472–483. doi:10.1007/978-3-642-39212-2_42. ISBN 978-3-642-39211-5.
  15. ^ Dirnberger, Michael; Neumann, Adrian; Kehl, Tim (2015). "NEFI: Network Extraction From Images". arXiv:1502.05241 [cs.CV].
  16. ^ Adamatzky, Andrew (2010). Physarum Machines: Computers from Slime Mould. World Scientific Series on Nonlinear Science, Series A. 74. World Scientific. ISBN 978-981-4327-58-9. Retrieved 2010-10-31.
  17. ^ Jump up to: a b Andrew, Adamatzky (2010). "Slime mould logical gates: exploring ballistic approach". Applications, Tools and Techniques on the Road to Exascale Computing (IOS Press, ), Pp. 2012: 41–56. arXiv:1005.2301. Bibcode:2010arXiv1005.2301A.
  18. ^ Jump up to: a b c Adamatzky, Andrew (2008-08-06). "Steering plasmodium with light: Dynamical programming of Physarum machine". arXiv:0908.0850 [nlin.PS].
  19. ^ Adamatzky, Andrew (31 May 2011). "On attraction of slime mould Physarum polycephalum to plants with sedative properties". Nature Precedings. doi:10.1038/npre.2011.5985.1.
  20. ^ Night, Will (2007-05-17). "Bio-sensor puts slime mould at its heart". New Scientist. Retrieved 2011-06-22.
  21. ^ Night, Will (2006-02-13). "Robot moved by a slime mould's fears". New Scientist. Retrieved 2011-06-22.
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