3. Purple Corn Origin, Distribution and Ecology

Origin: Zea mays L. is a domesticated plant species native to America. The exact centre of origin for this plant species remains a mystery. No wild individuals of this species have been found anywhere. Zea mays L. is believed to be the result of thousands of years of artificial selection carried out by ancient peoples of Central and South America. There exist several concluding archaeological and paleobotanical evidences indicating that Zea mays L. was already cultivated both in Mexico and Peru several thousand years ago.

The wild primitive individuals that turned into modern Zea mays L. are thought to be very similar to modern corn respect to their fundamental botanical characteristics.

On the other hand, Zea mays L. ‘Kculli’ is known to be native to Peru. The traditional cultivation of Zea mays L. ‘Kculli’ is restricted to the old area of influence of the Inca Empire, although modernly this cultivar or variety is also cultivated in several other countries.

Distribution: Today, Zea mays L. is grown in most countries throughout the world. Because of intensive cultivation and intensive use of fertilizers and herbicides, the United States is the most important Zea mays L. producer of the world, with more than 40% of world production. China, Brazil and Mexico are other important producers of this plant species.

Ecology: Corn is essentially a subtropical plant, but will grow now with its cultivars far into the temperate climate, as far north as Canada and Russia, where summers are long enough to produce good vegetative growth but rarely long enough to produce grain. It is known to grow from 58° N to 40° S latitude and from altitudes below sea level to 4 000 m in the Andes.

Zea mays L. is easily killed by frost. Most sweet corn is grown in areas with a mean temperature of 19–21°C during the summer months.

There exist many forms, cultivars or varieties of Zea mays L. and all of them present different characteristics. Since 1933 hybrid cultivars of Zea mays L. are being cultivated. The introduction of hybrid cultivars has improved yield in many places around the world and with any kind of soil. The most cultivated forms or groups of today are those obtained through a double crossbreeding; this means that two hybrids obtained from two self-pollinated strains are crossbred again. Recently, cultivation of new single crossbreeding strains is increasing because of their higher yields.

Hybrids do not transmit their vigor to their descendants, so that it is necessary to crossbreed every year the parental forms in order to obtain a new harvest of hybrid seeds. This work is done by seed-producer enterprises and some specialized farmers. Hybridization increases the cost of seeds, but the higher yield widely compensates the expenses. Yield increases comprised between 25% and 50% have been attributed to hybrid corn.

Researchers have also discovered mutant genes which induce a change in normal kernel from normal endosperm to flourish endosperm; this alteration occurs along with an increasing in tryptophan and lysine, two essential amino acids normally scarce in the natural corn proteins. The presence of either these mutant genes produces the so called lysine-rich corns, with a nutritional value in human diets equivalent to skimmed milk.

Pigs fed this kind of corn gain weight three times as fast as pigs fed normal corn. Agricultural scientists are now trying to transfer these genes into hybrid cultivars and parental strains; this discovery is said to be as important as the introduction of hybrid corn.

Corn grows well with early potatoes, legumes, dill, cucurbits and sunflowers, it dislikes growing with tomatoes.

· Plagues: Zea mays L. is susceptible to numerous plagues. There exists a big amount of fungus that infect roots, stems and ears; all of them reduce directly or indirectly the yield and affect kernel quality.
Galls incident to this disease develop on any of the aboveground parts of the plant and may become several centimeters in diameter. In the earlier stages they are white or gray, later becoming black. When mature, they rupture, releasing the dense powdery mass of black spores inside. No highly resistant cultivars so far are available. Rot diseases of roots, stalks and ears of corn are caused by a number of different fungi and are widely distributed.

Viruses are also important disease-causing agents in Zea mays L. The mosaic and rachitis are two important diseases of Zea mays L. caused by virus that are transmitted by insects such as a kind of little cicada. When viruses attack during an early stage, the reduction of yield could be serious.

The number of insect species that cause diseases in Zea mays L. is uncountable. Cornworm attacks the grains from the interior of the cob and devours the whole grain. European corn borer attacks especially the stems. In recent years, corn-root worm, the name used for the tinny larva of a crisomelid scarab that eats the roots of young plants, has caused abundant losses.

More than 300 different insect pests are known to attack corn, of which over 160 are particularly injurious. Most destructive are corn ear worm, European corn borer, grasshoppers, cutworms, rootworms, armyworms, sugarcane borer, grain weevils, various kinds of aphids, white grubs and several kinds of beetles, bugs and borers.

Corn smut probably is the most common disease of corn. Nematodes are also serious problems.

· Soil: Deep, naturally rich, easily tilled soil is preferred. Corn grows on great variety of soil types. This plant species prefers light (sandy), medium (loamy) and heavy (clay) soils and requires well-drained soil. It requires moist soil.

· Temperature: Annual temperature of 4.9ºC to 28.5°C (mean of 19.2).

· Rainfall: Annual rainfall of 750 mm or more is required for adequate moisture. Ranging from Boreal Moist to Rain through Tropical Desert to Wet Forest Life Zones, corn is reported to tolerate annual precipitation of 2.3 to 41.0 dm (mean of 12.2).

· pH requirements: The plant prefers slightly acid to neutral soils (6.6 to 7.5, 5.5 to 6.8 pH or 4.3 to 8.7).

· Light: Zea mays L. cannot grow in the shade.

· Propagation: Propagated only from seed. A deep, firm seedbed, free of clods, trash and surface irregularities should be prepared, either in the spring, or preferably on moderately heavy to heavy soil, in the fall and left rough over winter, thus allowing them to be worked and planted earlier in the spring. Light soil should be kept covered during the winter to prevent erosion and worked in the early spring.