Corn (Zea mays)
The Latin name for this species is mays and maize is the correct title for this group of plants. The plants many of us grow for corn on the cob, or “sweet corn” as it is sometimes called, is Z. mays ssp. rugosa, and was cultivated for its high sugar content. Many varieties of maize are grown for dried, fully mature seed, which is eaten as a grain, but sweet corn is picked before the seeds mature fully, before its sugars convert back into starch. This is why fresh corn must be eaten fairly quickly after harvest, before it degrades and becomes starchy. Many hybrids have been developed that retain their sweetness for longer periods, mature uniformly, and ship well.
Maize, including sweet corn, is produced in terrific quantities throughout the Americas, with the United States growing over 300 million metric tons each year alone. The crop was grown and celebrated by Mesoamerican peoples as long as 9,000 years ago, and forms the dietary base for scores of early American civilizations. Many Indian tribes also exploited the plant for its medicinal qualities: The Cherokee used it to treat skin blemishes and kidney stones; the Navajo created a poultice for sore throats; and the Tewa used it as to treat swelling, heart palpitations, and as an aid for menstruating women. The Iroquois people provided the first record of growing sweet corn to European settlers in 1779.
Corn, however it is eaten, is high in carbohydrates, sugars, protein, vitamins, magnesium, and potassium. The edible portions of sweet corn contain about 75% water. Cooking reduces the amount of usable vitamin C in sweet corn, but increases the quantity of ferulic acid, which is thought to be a powerful antioxidant, and seems to provide several health benefits.
The original corn, called “field corn,” had a high content of starch over sugar. Sweet corn occurs as a mutation in field corn and was grown by several Native American tribes. The Iroquois gave the first recorded sweet corn (called papoon) to European settlers in 1779. It soon became a popular food.
Crop breeders isolated several cultivars of sweet corn that would produce genetically similar offspring seeds. These include Golden Bantam, Pink Popcorn, Calico Popcorn, and Bloody Butcher. There are many others, including quite a few Mexican varieties.
Hybridization crosses the pollen of one variety with the receptive female flowers of another. The seeds that result are hybrid seeds. Hybridization allowed for more uniform maturity, improved quality, and disease resistance.
The genes that enhance the sugar content and shelf life of sweet corn are carried in the plants’ pollen. In order for the genetic expression to be true, the variety may need to be isolated to prevent cross-pollination. SU, SE, and SH2 are the names of isolated gene groups. These are hybrids, not GMO / GEO.
SU varieties (developed circa 1902) have modest amounts of sugar in their kernels, and they tend to have decent corn flavor. But their conversion of sugar to starch is rapid, so they have a narrow harvest window before flavour deteriorates. They tend to have good plant vigour. To avoid cross-pollination and poor quality, SU varieties must be isolated from field corn and popcorn. They must also be isolated from the supersweet (sh2) group.
The SE gene (developed in the 1950s) gives varieties improved eating quality over SU varieties by slightly increasing the level and changing the types of sugars in the kernels. SE varieties also have a very tender pericarp (the outer layer of the kernel). The SE gene does not slow the conversion of sugars to starch but the harvest window is slightly longer than with SU varieties because of elevated sugar levels. SE varieties do not require isolation from SU varieties, but they do require isolation from SH2 and field or popcorn.
Supersweet or shrunken-2 types (also 1950s) have four to ten times the sugar content of normal sugar (SU) types and with proper handling are able to be stored for up to 10 days. They are less hardy than even sugary extender (SE) types, requiring higher soil temperature for germination, precise planting depth, and isolation from all other corn pollen for optimum results. The name derives from the shrunken, shrivelled appearance of the dried kernel which is low in starch. The SH2 gene slows the conversion of simple sugars to starch, so supersweet varieties have a much wider harvest window than other types.
Synergistic varieties combine more than one line of genetics on the same ear. The first varieties developed of this type have 25% sh2, 25% se and 50% su kernels on the cob, but now different combinations are possible. There is an increasing number of brand names and trademarks that cover specific genetic combinations under this general type.
The town of Jarvis, in southern Ontario, celebrates Cornfest each August. Jarvis really lets its hair down as it hosts a serious baseball competition, car show, live music, equestrian events, crafts, a midway, and of course, lots and lots of corn to eat.
