HUITLACOCHE: CHARACTERISTICS, HABITAT, LIFE CYCLE, PROPERTIES - BIOLOGY - 2024

The huitlacoche or cuitlacoche (Ustilago maydis) is a Basidiomycota fungus of the Ustilaginaceae family that, within its life cycle, has two phases, a saprophytic and a parasitic one. In this last phase, it affects corn, producing a disease called "charcoal" or "common corn blight".

The disease can attack any part of the plant, producing tumor-like galls of variable size, even exceeding 30 cm in diameter. When galls appear on the kernels it is because the infection has occurred in the ovaries, and the kernels most affected are those found at the apex of the ear.

Ustilago maydis. Taken and edited from: H. Zell.

The disease is considered a pest of crops almost worldwide and diseased plants are usually destroyed to prevent the spread of the fungus. However, in Mexico they consider the fungus a delicacy, and even induce, both artisanal and commercially, its propagation.

Huitlacoche presents in its composition important amounts of antioxidants, fiber, vitamins, as well as lysine and amino acids. In addition, the researchers suggest that it has properties that are auxiliary in the prevention of cancer and other diseases.

characteristics

Ustilago maydis presents an asexual phase in the form of yeast characterized, among other aspects, because when developed in a solid PDA culture medium it presents concave colonies, of a light creamy, matte color, which turn brown after 8 days after sowing. Additionally, the colony is urease positive.

The pathogenic phase of sexual reproduction can affect all aerial parts of the plant, especially the developing meristematic tissues. Symptoms appear as chlorosis, anthocyanin spots, and finally the development of tumors or galls.

The galls are covered by a layer of shiny light green or light gold tissue and are formed by hypertrophied cells of the host, as well as by tissues and spores of the fungus, the latter are dark blue. The gills are somewhat fleshy and firm and initially light in color and darken with time.

The spores inside the galls darken as they mature and turn into a dusty mass, and their color turns brown or black. These spores vary in shape from globose to elongated and irregular, measuring 7-11 µm x 7-13 µm, their cell wall is 0.5 µm thick, and they are finely covered with spines.

The release of spores occurs by breaking the layer of tissue that covers the galls. Mature galls can exceed 30 cm, but normal is 15 cm and not more than 1.2 cm in the case of leaf galls.

Taxonomy

Ustilago maydis is a Basidiomycota fungus belonging to the class Ustilaginomycetes, order Ustilaginales, family Ustilaginaceae. This family currently comprises about 17 genera and more than 600 species.

The genus Ustilago was described by the mycologist Christian Hendrik Persoon using Ustilago hordei as the type species. It is currently represented by about 200 species, all of them parasitic on grasses.

The taxon Ustilago maydis was coined by the Swiss botanist Augustin Pyramus de Candolle (abbreviated DC according to the rules governing the nomenclature of fungi), and later circumscribed by the mycologist August Carl Joseph Corda.

Synonymy of the species include Caeoma zeae, Lycoperdon zeae, Uredo maydis, Uredo segetum, and Ustilago zeae.

Habitat and distribution

The habitat of the huitlacoche or cuitlacoche is mainly associated with corn, although it can affect other grasses. In its saprophytic phase, the fungus develops as a unicellular organism that receives the name of sporidium and inhabits the corn plant. In its parasitic phase it develops inside it.

The distribution of Ustilago maydis is worldwide, being able to be present in any place where corn is grown.

Lifecycle

The life cycle of Ustilago maydis is complex, on the one hand it presents a unicellular and uninucleated phase, which reproduces asexually and is called sporidium; and on the other, a multicellular dikaryote phase that is going to reproduce sexually.

Sporidium is non-infective, has a saprophytic diet and develops outside the corn plant. Sporidium can reproduce by budding. The passage from this saprophytic phase to the parasitic phase is genetically determined by alleles of sexual type a and b.

If a pair of sexually compatible sporidia for the a locus are found, each forms a germination tube towards the other. When these tubes meet, plasmagamy or fusion of the cells of both tubes occurs, without the nuclei uniting, resulting in a dikaryote structure known as the infective filament.

The infective filament will seek the appropriate place of penetration into the internal tissues of the host. When it is inside the plant, the development of a dicariont mycelium will take place.

The mycelium develops inside the host without initially killing the host cells. This mycelium causes alterations in the cell growth of the host giving rise to galls. In the gills, individual cells of the dicariont mycelium will separate and undergo karyogamy (fusion of nuclei) to form diploid cells called teliospores.

These teliospores develop thick black walls that are in turn responsible for the coloration of the galls. Then the teliospores germinate producing a structure called promicelium in which meiosis occurs and four haploid cells are produced that are released into the environment to restart the cycle.

Spores of Ustilago maydis. Taken and edited from: 2011-08-27_Ustilago_maydis_ (DC.) _ Corda_183839.jpg: This image was created by user Alan Rockefeller (Alan Rockefeller) at Mushroom Observer, a source for mycological images. You can contact this user here. English - Spanish - français - italiano - македонски - português - +/− derivative work: Ak ccm.

Applications

In most countries of the world, huitlacoche or cuitlacoche is considered a pest and contaminated plants are eliminated to prevent the rapid spread of the disease.

However, in Mexico it has been used as food since the time of the Aztec culture. The fungus is consumed when the galls appear and before they mature. It can be consumed fresh as well as canned and its price is several times higher than that of uninfected corn.

The form of consumption is in the form of a stew or as part of other dishes such as tortillas, tacos, quesadillas, soups, among others. The flavor of the mushroom is quite pleasant, with some resemblance to that of Morcella mushrooms, but with a slight smoky and acid touch. Its texture is also appreciated.

Little by little, the fungus has been gaining adherents in Europe and the United States, especially in haute cuisine restaurants, where it reaches quite high values.

Other uses

The non-infective phase of Ustilago maydis is used as a model organism for research, which has been favored by the fact that its genome has been fully described.

Researchers have used this fungus to study plant disease, as well as in genetic manipulation tests and to learn about some aspects of the genetics of its host, using the homologous recombination method in DNA repair.

Additionally, Ustilago maydis is capable of biosynthesizing a series of high-value compounds, such as ustilágic, malic and hydroxyparaconic acids, for which the biotechnology industry uses it more and more.

Culture

As already mentioned, in most of the countries of the world the huitlacoche or cuitlacoches considered a pest, for which there is a fight for its eradication from the crops, however, in Mexico not only the naturally infected corn is used but also cultivate the fungus by artificial propagation.

The mechanisms of artificial propagation are empirical infection, practiced directly by some producers, and the inoculation of spores obtained by culture on potato dextrose agar.

The growing interest in the fungus for food purposes has even allowed some states in the United States, such as Florida and Pennsylvania to obtain authorization from the Department of Agriculture (USDA, for its acronym in English) to carry out the inoculation of the fungus, to Despite the fact that the rest of the states are fighting for its eradication.

Sale of the Huitlacoche in Soriana Oaxaca Mexico. Taken and edited from: Nsaum75 at English Wikipedia.

Nutritional properties

Ustilago maydis has been classified as a nutraceutical food, that is, it has both nutritional, medicinal or pharmaceutical properties. These properties include high amounts of the following compounds:

Soluble dietary fiber

The fiber in food helps the intestinal transit to be adequate, by stimulating the peristaltic movements of the digestive tract.

Antioxidants

Antioxidant foods help fight free radicals and therefore prevent premature aging.

Vitamins and essential amino acids

In addition to having high levels of various vitamins, huitlacoche contains several essential amino acids, that is, they are necessary for the proper functioning of the human body. However, the body does not synthesize them, so they must be included in the diet.

Among these amino acids is lysine, which helps the adequate absorption of calcium, the formation of collagen, the release of growth hormone and mental development, in addition to strengthening the immune system.

Additionally, all these components help to control blood sugar and cholesterol levels in the long term and it has been suggested that they also help prevent some forms of cancer.

References

1. CW Basse, et al. (2004), Ustilago maydis, model system for analysis of the molecular basis of fungal pathogenicity. Mol Plant Pathol.
2. Corn smut. On Wikipedia. Recovered from: en.wikipedia.org.
3. Ustilago maydis. Recovered from: esacademic.com.
4. E. Guevara-Vázquez, E. Valadez-Moctezuma, M. Acosta-Ramos, T. Espinosa-Solares & C. Villanueva-Verduzco (2009). Identification of yeasts associated with huitlacoche. Chapingo Magazine Horticulture Series.
5. JK Pataky (1999). Production of huitlacoche on sweet corn. Hortscience.
6. F. Banuett & I. Herskowitz (1996). Discrete developmental stages during teliospore formation in the corn smut fungus, Ustilago maydis. Development.
7. Ustilago maydis, Corn coal. Recovered from: asturnatura.com