Corn smut

 

Corn smut
Huitlacoche
Scientific classification
Kingdom:	Fungi
Subkingdom:	Dikarya
Phylum:	Basidiomycota
Subphylum:	Ustilaginomycotina
Class:	Ustilaginomycetes
Order:	Ustilaginales
Genus:	Ustilago
Species:	U. maydis
Binomial name
Ustilago maydis (Persoon) Roussel

Corn smut (Ustilago maydis) is a pathogenic plant fungus that causes smut disease on maize and teosinte (Euchlena mexicana). The fungus forms galls on all above-ground parts of corn species, and is known in Mexico as huitlacoche; it is eaten, usually as a filling, in quesadillas and other tortilla-based foods, and soups.

Etymology

In Mexico, corn smut is known as huitlacoche ([witɬakotʃe], sometimes spelled cuitlacoche). This word entered Spanish in Mexico from classical Nahuatl, though the Nahuatl words from which huitlacoche is derived is debated. In modern Nahuatl, the word for huitlacoche is cuitlacochin, and some sources deem cuitlacochi to be the classical form.

Some sources give the etymology as coming from the Nahuatl words cuitla ("excrement" or "rear-end") and cochtli ("sleeping", from cochi="to sleep"), thus giving a combined meaning of "sleeping/hibernating excrement".

A second group of sources deem the word to mean "raven's excrement". These sources appear to be combining the word cuitlacoche for "thrasher" with cuitla, meaning "excrement". However, the avian meaning of cuitlacoche derives from the Nahuatl word cuicatl ("song"), itself from the verb cuica ("to sing"). 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 excrement", using cuitla again and tlaole ("maize"). This requires the linguistically unlikely evolution of tlaole into tlacoche.

Characteristics

Although it can infect any part of the plant, it usually enters the ovaries and replaces the normal kernels of the cobs with large, distorted tumors analogous to mushrooms. These tumors, or "galls", are made up of much-enlarged cells of the infected plant, fungal threads, and blue-black spores. The spores give the cob a burned, scorched appearance. The generic name Ustilago comes from the Latin word ustilare (to burn).

Huitlacoche grows best during times of drought in a 78 to 93 °F (26 to 34 °C) temperature range. Aztecs purposely inoculated corn with the spores by scratching their corn plants at the soil level with a knife—thereby allowing the water-borne spores easy entrance into the plant.^{[citation needed]}

Life cycle

Ustilago maydis diploid teleospores

Ustilago maydis haploid sporidia

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, they switch to a different mode of growth. First, they send out conjugation tubes to find each other, 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 U. maydis requires infection of the plant to grow and differentiate, 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.

Mature spores are released from the tumors and spread by rain and wind. Under appropriate conditions, a probasidium is formed in which meiosis occurs. Resulting haploid nuclei migrate into elongated single cells. These cells detach from the probasidium to become the sporidia, thus completing the life cycle.

Uses

Model organism

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 model organism.

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. 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.

Culinary uses

Huitlacoche corn taco

Quesadilla de huitlacoche, as it's often served in central Mexico

Huitlacoche for sale in the produce department of a Soriana store in Mexico

Smut feeds on the corn plant and decreases the yield. Usually, smut-infected crops are destroyed. Some farmers may also choose to prepare corn silage out of the smutted corn. It is most popular in Mexico, where it is known as huitlacoche and can be regularly found as an option in meals. The consumption of corn smut originates from ancient Aztec cuisine and is still considered a delicacy in Mexico, even being preserved and sold for a significantly higher price than corn. 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.

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. This dinner tried to get Americans to eat more of it by renaming it the Mexican truffle.^{[citation needed]}

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.

Recipes of Mexico

A favorite and simple Mexican-style succotash can be made from chorizo, onions, garlic, serano 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 Mayan favorite on the Riviera Maya (Cancun to Tulum) is to add huitlacoche to omelettes. Once again, its earthy flavors bond with the fats that cook the eggs to mellow the flavors into a truffle-like taste.

An important thing to note about huitlacoche is that 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.

Availability

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. Some farmers' markets and organic growers are endeavoring to bring fresh huitlacoche to their customers and local food service trade.

See also

• Medicinal mushrooms

References

• McGee, Harold (2004). On Food and Cooking (Revised Edition). Scribner. ISBN 0-684-80001-2.  p 349, "Huitlacoche, or Corn Smut".

External links

• U. maydis Genome at the Broad Institute
• MUMDB giving easy access to U. maydis genes