Corn smut | |
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Mycosarcoma maydis diploid teleospores | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Basidiomycota |
Class: | Ustilaginomycetes |
Order: | Ustilaginales |
Family: | Ustilaginaceae |
Genus: | Mycosarcoma |
Species: | M. maydis |
Binomial name | |
Mycosarcoma maydis | |
Synonyms | |
Corn smut | |
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![]() Huitlacoche | |
Common names | huitlacoche (Mexico), blister smut of maize, boil smut of maize, common smut of maize |
Causal agents | Mycosarcoma maydis |
Hosts | maize and teosinte |
EPPO Code | USTIMA |
Distribution | Worldwide, where corn is grown [3] [4] |
Corn smut is a plant disease caused by the pathogenic fungus Mycosarcoma maydis. One of several cereal crop pathogens called smut, the fungus forms galls on all above-ground parts of corn species such as maize and teosinte. The infected corn is edible; in Mexico, it is considered a delicacy, called huitlacoche, [5] often eaten as a filling in quesadillas and other tortilla-based dishes, as well as in soups.
![]() | This section may require cleanup to meet Wikipedia's quality standards. The specific problem is: Insertion of "excrescence" correction done very incorrectly.(January 2024) |
In Mexico, corn smut is known as huitlacoche (Spanish pronunciation: [(ɡ)witlaˈkotʃe] , sometimes spelled cuitlacoche). This word entered Spanish in Mexico from Classical Nahuatl, though the Nahuatl words from which huitlacoche is derived are debated. In modern Nahuatl, the word for huitlacoche is cuitlacochin (Nahuatl pronunciation: [kʷit͡ɬɑˈkot͡ʃin] ), and some sources deem cuitlacochi to be the classical form. [6]
Some sources wrongly give the etymology as coming from the Nahuatl words cuitlatl [ˈkʷit͡ɬɑt͡ɬ] ("excrement" or "rear-end", actually meaning "excrescence") and cochtli [ˈkot͡ʃt͡ɬi] ("sleeping", from cochi "to sleep"), thus giving a combined mismeaning of "sleeping/hibernating excrement", [6] [7] but actually meaning "sleeping excrescence", referring to the fact that the fungus grows between the kernels and impedes them from developing, thus they remain "sleeping".
A second group of sources deem the word to mean "raven's excrement". [8] [9] These sources appear to be combining the word cuitlacoche for "thrasher" [10] with cuitla, meaning "excrement", actually meaning "excrescence". However, the avian meaning of cuitlacoche derives from the Nahuatl word "song" cuīcatl [ˈkʷiːkɑt͡ɬ] , itself from the verb "to sing" cuīca [ˈkʷiːkɑ] . [6] This root then clashes with this reconstruction's second claim that the segment cuitla- comes from cuitla ("excrement").
One source derives the meaning as "corn excrescence", using cuītla again and "maize" tlaōlli [t͡ɬɑˈoːlːi] . [11] This requires the linguistically unlikely evolution of tlaōlli "maize" into tlacoche.
In Peru, it is known as chumo or pacho.
Mycosarcoma maydis is the best known and studied of the Ustilaginomycetes, a sub class of basidiomycota, and so is often used as the exemplar species when talking about its entire class. [12]
Formerly it was placed in genus Ustilago, but in 2016 it was placed in genus Mycosarcoma. [13]
The fungus infects all parts of the host plant by invading the ovaries of its host. The infection causes the corn kernels to swell up into tumor-like galls, whose tissues, texture, and developmental pattern are mushroom-like. The galls grow to 4 to 5 inches in diameter. These galls are made up of hypertrophied cells of the infected plant, along with resulting fungal threads, and blue-black spores. [14] These dark-colored spores give the cob a burned, scorched appearance.[ citation needed ]
When grown in the lab on very simple media, it behaves like baker's yeast, forming single cells called sporidia. These cells multiply by budding off daughter cells. When two compatible sporidia meet on the surface of the plant, however, they switch to a different mode of growth. First, they produce one or another pheromone, and begin producing one or the other type of pheromone receptor - this depends on mating type a or b, as determined by alleles at two unlinked mating loci. If this signalling is successful they then send out conjugation tubes to find each other, [12] after which they fuse and make a hypha to enter the maize plant. Hyphae growing in the plant are dikaryotic; they possess two haploid nuclei per hyphal compartment. In contrast to sporidia, the dikaryotic phase of M. maydis only occurs during successful infection of a maize plant, and cannot be maintained in the laboratory.
Proliferation of the fungus inside the plant leads to disease symptoms such as chlorosis, anthocyanin formation, reduced growth, and the appearance of tumors harboring the developing teliospores. These teliospores help to overwinter the pathogen into the next season. They survive in the soil. [15] [16]
Mature tumors release spores that are dispersed by rain and wind. Under appropriate conditions, a metabasidium is formed in which meiosis occurs. Resulting haploid nuclei migrate into elongated single cells. These cells detach from the metabasidium to become the sporidia, thus completing the life cycle.
Plants have evolved efficient defense systems against pathogenic microbes. A rapid plant defense reaction after pathogen attack is the oxidative burst, which involves the production of reactive oxygen species at the site of the attempted invasion. As a pathogen, M. maydis can respond to such an oxidative burst by an oxidative stress response, regulated by gene YAP1. This response protects M. maydis from the host attack, and is necessary for the pathogen's virulence. [17] Furthermore, M. maydis has a well-established recombinational DNA repair system. [18] This repair system involves a homolog of Rad51 that has a very similar sequence and size to its mammalian counterparts. This system also involves a protein, Rec2 that is more distantly related to Rad51, and Brh2 protein that is a streamlined version of the mammalian Breast Cancer 2 (BRCA2) protein. When any of these proteins is inactivated, sensitivity of M. maydis to DNA damaging agents is increased. Also mitotic recombination becomes deficient, mutation frequency increases and meiosis fails to complete. These observations suggest that recombinational repair during mitosis and meiosis in M. maydis may assist the pathogen in surviving DNA damage arising from the host's oxidative defensive response to infection, as well as from other DNA damaging agents.
Mycosarcoma maydis is known to produce four Gα proteins, and one each of Gβ and Gγ. [12]
Losses from corn smut can vary greatly; however, annual yield losses rarely exceed 2% when resistant cultivars are planted. This disease can have a large economic impact on sweet corn, specifically when smut galls replace the kernels. There are many ways to control and manage corn smut; however, corn smut cannot be controlled by any common fungicide at this time, as M. maydis infects individual corn kernels instead of infecting the entire cob, like head smut. [19]
Some beneficial ways to contain corn smut include resistant corn plants, crop rotation, and avoiding mechanical injury to the plant. A mechanical injury can cause the corn to become easily accessible to M. maydis, enhancing infection. Additionally, clearing the planting area of debris can help control corn smut, as the teliospores from corn smut overwinter in debris. This is not the best practice, though, because corn smut can also overwinter in the soil; crop rotation is recommended. Lastly, as excess nitrogen in the soil augments infection rate, using fertilizer with low nitrogen levels, or just limiting the amount of nitrogen in the soil proves to be another way to control corn smut. [20]
Although not all the conditions that favor growth of Mycosarcoma maydis are known, there are certain environments where corn smut seems to thrive, depending on both abiotic and biotic factors. Hot and dry weather during pollination followed by a heavy rainy season appear to improve the pathogenicity of corn smut. [21] Furthermore, excess manure (and therefore nitrogen) in the soil also increases pathogenicity. Not only do these abiotic factors increase infectability, they also increase disease spread. High winds and heavy rain also increase disease spread as the spores of corn smut can be more easily transmitted. Other biotic factors largely have to do with the extent by which humans interact with the corn and corn smut. If corn debris is not cleared at the end of the season, the spores can overwinter in the corn fragments and live to infect another generation. [22] Finally, humans wounding the corn (with shears or other tools) present the opportunity for corn smut to easily enter the plant.
Smut feeds on the corn plant and decreases the yield. Smut-infected crops are often destroyed, although some farmers use them to prepare silage. However, the immature infected galls are still edible, and in Mexico they are highly esteemed as a delicacy. It is known as huitlacoche, and sold for a significantly higher price than uninfected corn. The consumption of corn smut in Mexico originated directly from Aztec cuisine. [23] For culinary use, the galls are harvested while still immature — fully mature galls are dry and almost entirely spore-filled. The immature galls, gathered two to three weeks after an ear of corn is infected, still retain moisture and, when cooked, have a flavor described as mushroom-like, sweet, savory, woody, and earthy. Flavor compounds include sotolon and vanillin, as well as the sugar glucose.
Huitlacoche is a source of the essential amino acid lysine, which the body requires but cannot manufacture. It also contains levels of beta-glucans similar to, and protein content equal or superior to, most edible fungi. [24]
The fungus has had difficulty entering into the American and European diets as most farmers see it as blight, despite attempts by government and high-profile chefs to introduce it. In the mid-1990s, due to demand created by high-end restaurants, Pennsylvania and Florida farms were allowed by the United States Department of Agriculture (USDA) to intentionally infect corn with huitlacoche. Most observers consider the program to have had little impact,[ citation needed ] although the initiative is still in progress. The cursory show of interest is significant because the USDA has spent a considerable amount of time and money trying to eradicate corn smut in the United States. Moreover, in 1989, the James Beard Foundation held a high-profile huitlacoche dinner, prepared by Josefina Howard, chef at Rosa Mexicano restaurant. [25] This dinner tried to get Americans to eat more of it by renaming it the "Mexican truffle" and it is often compared to truffles in food articles describing its taste and texture. [25] [26] [27]
Native American tribes in North America ate corn smut as well. The Hidatsa tribe of North Dakota's practice of preparing and eating corn smut is described vividly in Buffalo Bird Woman's Garden . [28]
Native Americans of the American Southwest, including the Zuni people, have used corn smut in an attempt to induce labor. It has similar medicinal effects to ergot, but weaker, due to the presence of the chemical ustilagine. [29]
A simple Mexican-style succotash can be made from chorizo, onions, garlic, serrano peppers, huitlacoche, and shrimp with salsa taquera. The mild, earthy flavors of the huitlacoche blend nicely with the fats of the chorizo and bond to mellow out the heat from the peppers and salsa.
Another Maya favorite on the Riviera Maya (Cancun to Tulum) is to add huitlacoche to omelettes. Its earthy flavors bond with the fats that cook the eggs to mellow the flavors into a truffle-like taste.
Huitlacoche is also popular in quesadillas with Mexican cheese, sautéed onions, and tomatoes.
The blueish color transforms into the recognizable black color only with heat. Any dish with huitlacoche must include a slow simmer of the fungus until it becomes black, which also removes most of the starch of the corn, and what is left is a black oily paste.
In Mexico, huitlacoche is mostly consumed fresh and can be purchased at restaurants or street or farmer's markets throughout the country and, to a much lesser extent, can also be purchased as a canned good in some markets and via the internet. Farmers in the countryside spread the spores around intentionally to create more of the fungus. In some parts of the country, they call the fungus "hongo de maiz", i.e. "maize fungus". [30]
When corn smut grows on a corn cob, it changes the nutritional worth of the corn it affects. Corn smut contains more proteins than the uninfected grains normally do. The amino acid lysine, of which corn contains very little, abounds in corn smut. [31]
The yeast-like growth of U. maydis makes it an appealing model organism for research, although its relevance in nature is unknown. The fungus is exceptionally well-suited for genetic modification. This allows researchers to study the interaction between the fungus and its host with relative ease. The availability of the entire genome is another advantage of this fungus as a model organism. [32]
U. maydis is not only used to study plant disease, but it also is used to study plant genetics. In 1996, a study on U. maydis genetics led to the discovery of synthesis-dependent strand annealing, a method of homologous recombination used in DNA repair. [33] Other studies in the fungus have also investigated the role of the cytoskeleton in polarized growth.[ citation needed ] It is largely due to work with U. maydis that the function of the breast-cancer gene BRCA2 is now known. [34] The fungus is mostly studied as model organism for host pathogen interaction and delivery of effectors protein.
Mycosarcoma maydis is able to produce a broad range of valuable chemicals such as ustilagic acid, itaconic acid, malic acid, and hydroxyparaconic acid. This ability is gaining corn smut more relevance to industrial applications. [35]
Basidiomycota is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basidiomycota includes these groups: agarics, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and Cryptococcus, the human pathogenic yeast.
Rusts are fungal plant pathogens of the order Pucciniales causing plant fungal diseases.
The smuts are multicellular fungi characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for 'dirt' because of their dark, thick-walled, and dust-like teliospores. They are mostly Ustilaginomycetes and comprise seven of the 15 orders of the subphylum. Most described smuts belong to two orders, Ustilaginales and Tilletiales. The smuts are normally grouped with the other basidiomycetes because of their commonalities concerning sexual reproduction.
Ustilago is a genus of approximately 200 smut fungi, which are parasitic on grasses. 170 species are accepted by Wijayawardene et al. 2020; After phylogenetic research certain species in Ustilago, Macalpinomyces, and other genera in the Ustilaginaceae clade have been moved to other genera like Mycosarcoma.
Fungi are a diverse group of organisms that employ a huge variety of reproductive strategies, ranging from fully asexual to almost exclusively sexual species. Most species can reproduce both sexually and asexually, alternating between haploid and diploid forms. This contrasts with most multicellular eukaryotes such as mammals, where the adults are usually diploid and produce haploid gametes which combine to form the next generation. In fungi, both haploid and diploid forms can reproduce – haploid individuals can undergo asexual reproduction while diploid forms can produce gametes that combine to give rise to the next generation.
Sugarcane smut is a fungal disease of sugarcane caused by the fungus Sporisorium scitamineum. The disease is known as culmicolous, which describes the outgrowth of fungus of the stalk on the cane. It attacks several sugarcane species and has been reported to occur on a few other grass species as well, but not to a critical amount. The most recognizable characteristic of this disease is a black or gray growth that is referred to as a "smut whip". Resistance to sugarcane smut is the best course of action for management, but also the use of disease free seed is important. On smaller scale operations treatments using hot water and removing infected plants can be effective. The main mode of spore dispersal is the wind but the disease also spreads through the use of infected cuttings. Sugarcane smut is a devastating disease in sugarcane growing areas globally.
The Ustilaginales are an order of fungi within the class Ustilaginomycetes. The order contained 8 families, 49 genera, and 851 species in 2008.
The Ustilaginomycotina is a subdivision within the division Basidiomycota of the kingdom Fungi. It consists of the classes Ustilaginomycetes and Exobasidiomycetes, and in 2014 the subdivision was reclassified and the two additional classes Malasseziomycetes and Monilielliomycetes added. The name was first published by Doweld in 2001; Bauer and colleagues later published it in 2006 as an isonym. Ustilagomycotina and Agaricomycotina are considered to be sister groups, and they are in turn sister groups to the subdivision Pucciniomycotina.
Sporisorium reilianum Langdon & Full., (1978), previously known as Sphacelotheca reiliana, and Sporisorium reilianum, is a species of biotrophic fungus in the family Ustilaginaceae. It is a plant pathogen that infects maize and sorghum.
Exobasidium vaccinii, commonly known as “red leaf disease,” or “Azalea Gall,” is a biotrophic species of fungus that causes galls on ericaceous plant species, such as blueberry and azalea. Exobasidium vaccinii is considered the type species of the Exobasidium genus. As a member of the Ustilagomycota, it is a basidiomycete closely related to smut fungi. Karl Wilhelm Gottlieb Leopold Fuckel first described the species in 1861 under the basionym Fusidium vaccinii, but in 1867 Mikhail Stepanovich Voronin later placed it in the genus Exobasidium. The type specimen is from Germany, and it is held in the Swedish Museum of Natural History. Exobasidium vaccinii, in current definition from John Axel Nannfeldt in 1981, is limited on the host Vaccinium vitis-idaea. This idea is used in most recent papers on E. vaccinii.
Dimorphic fungi are fungi that can exist in the form of both mold and yeast. This is usually brought about by change in temperature and the fungi are also described as thermally dimorphic fungi. An example is Talaromyces marneffei, a human pathogen that grows as a mold at room temperature, and as a yeast at human body temperature.
A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as one of the traditional eukaryotic kingdoms, along with Animalia, Plantae and either Protista or Protozoa and Chromista.
Grey leaf spot (GLS) is a foliar fungal disease that affects maize, also known as corn. GLS is considered one of the most significant yield-limiting diseases of corn worldwide. There are two fungal pathogens that cause GLS: Cercospora zeae-maydis and Cercospora zeina. Symptoms seen on corn include leaf lesions, discoloration (chlorosis), and foliar blight. Distinct symptoms of GLS are rectangular, brown to gray necrotic lesions that run parallel to the leaf, spanning the spaces between the secondary leaf veins. The fungus survives in the debris of topsoil and infects healthy crops via asexual spores called conidia. Environmental conditions that best suit infection and growth include moist, humid, and warm climates. Poor airflow, low sunlight, overcrowding, improper soil nutrient and irrigation management, and poor soil drainage can all contribute to the propagation of the disease. Management techniques include crop resistance, crop rotation, residue management, use of fungicides, and weed control. The purpose of disease management is to prevent the amount of secondary disease cycles as well as to protect leaf area from damage prior to grain formation. Corn grey leaf spot is an important disease of corn production in the United States, economically significant throughout the Midwest and Mid-Atlantic regions. However, it is also prevalent in Africa, Central America, China, Europe, India, Mexico, the Philippines, northern South America, and Southeast Asia. The teleomorph of Cercospora zeae-maydis is assumed to be Mycosphaerella sp.
Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis.
Ustilago esculenta is a species of fungus in the Ustilaginaceae, a family of smut fungi. It is in the same genus as the fungi that cause corn smut, loose smut of barley, false loose smut, covered smut of barley, loose smut of oats, and other grass diseases. This species is pathogenic as well, attacking Manchurian wild rice, also known as Manchurian ricegrass, Asian wild rice, and wateroat. This grass is its only known host.
Zizania latifolia, known as Manchurian wild rice, is the only member of the wild rice genus Zizania native to Asia. It is used as a food plant. Both the stem and grain are edible. Gathered in the wild, Manchurian wild rice was an important grain in ancient China. A wetland plant, Manchurian wild rice is now very rare in the wild, and its use as a grain has completely disappeared in Asia, though it continues to be cultivated for its stems. A measure of its former popularity is that the surname Jiǎng, one of the most common in China, derives from this crop.
Ustilagic acid is an organic compound with the formula C36H64O18. The acid is a cellobiose lipid produced by the corn smut fungus Ustilago maydis under conditions of nitrogen starvation. The acid was discovered in 1950 and was proved to be an amphipathic glycolipid with surface active properties. The name comes from Latin ustus which means burnt and refers to the scorched appearance of the smut fungi.
Stenocarpella maydis (Berk.) Sutton is a plant pathogenic fungus and causal organism of diplodia ear and stalk rot. Corn and canes are the only known hosts to date. No teleomorph of the fungus is known.
Regine Kahmann is a German microbiologist and was Director at the Max Planck Institute for Terrestrial Microbiology in Marburg from 2000 to 2019. She was made a Foreign Member of the Royal Society (ForMRS) in 2020.
Mycosarcoma is a genus of fungus including M. maydis, sometimes called Ustilago maydis, 'corn smut fungus'. This genus seems to be a result of recent genetic testing showing that a new taxon is needed to better organize these species, previously thought unrelated. The six recognized species were in different genera originally until genetic testing showed their relations and a genus name was resurrected to split these species into a more fitting nomenclature.