In this article we will discuss about:- 1. Introduction to Maize 2. Origin and History of Maize 3. Botany 4. Growth Stages 5. Classification 6. Uses.
Introduction to Maize:
Maize or corn, popularly known as Makka or Makai in Hindi, is one of the most important cereal crops in the world agricultural economy both as food for man and feed for animals including poultry. It is also known as “queen of cereals”, because of very high yield potential. The maximum quantities of maize produced in the country are consumed as human food.
Both wet and dry milling industry separates the fraction of grain into germ, hull and endosperm to produce various products. Besides products, such as sleep concentration, gluten feed gallium meal, maize oil and maize oil cake are by-products of maize.
Starch is used in textile industry, paper industry, food industry etc. All the major sweeteners are commercially made from maize starch. Maize starch is a polymer of anhydrous glucose units (dextrose) and is the raw material for sweeteners Green cobs are roasted and consumed by people with great interest.
The grains of special variety called the ‘popcorn’, are characterized by a hard corneous interior structure are converted into the ‘popped’ form, which is the favourite food for children in urban areas. Several food dishes including chapattis are prepared out of maize flours and grains. It is also indirectly consumed because it is a key ingredient in the feed of cattle, poultry and swine. Livestock feed is the leading use.
Origin and History of Maize:
The place of maize origin is still debatable. Based on cytogenetical and molecular evidences, out of the 3 believed ancestors (popcorn, wild maize and teosinte), teosinte (Zea maxicana) is accepted as ancestor of maize. Tripartite theory of origin of maize states that – (a) cultivated maize originated from pod corn, (b) teosinte is a derivative of a hybrid maize and Tripsacum and (c) the majority of modem corn varieties are the product of admizture withteosinte or Tripsacum or both.
Maize is thought to have originated in tropical south central or southwestern Mexico. Scientists have discovered more than 300 distinct races of corn from Mexico, South America, Central America, and the Caribbean. The maize was introduced into Spain after the return of C. Columbus from America, and from Spain it reached to France, Italy and Turkey. The plant was grown in Europe as a garden curiosity. It was introduced into north-west Himalayas of India, probably in early 17th century through silk route.
Botany of Maize Plant:
Maize (Zea mays L.) belongs to the tribe, Tripsaceae (Maydeae) of the family Gramineae. It is a tall, determinate annual plant producing large, narrow, opposing leaves (about a tenth as wide as they are long), borne alternately along the length of a solid stem.
Stem:
The stem of the maize is erect, cylindrical, from 50 cm to 3 meters high and 2-3 cm thick. It is filled with loose parenchyma, has distinct nodes and internodes. The leaves grow alternatively on the opposite sides of the stem. They bear small hairs on them and number of leaves varies from 10-20.The upper leaves in com are more responsible for light interception and are major contributors of photosynthate to grain.
Root:
The root system is strong and fibrous, deeply penetrating into the soil. The maize caryopsis germinates through one embryonic root followed by seedling or seminal roots. Their principal function of seminal roots is to supply the maize plant with water and nutrients during the first 2-3 weeks of vegetation until the nodal roots develops and begin to function. The seminal roots are later replaced by permanent adventitious (nodal) roots that are originated from the crown present at the end of mesocotyl (3-4th leaf stage).
The lateral roots branch profusely, spread widely and penetrate deeply. The bulk of the maize roots are concentrated in the 30 cm soil layer. Besides these roots, ‘prop or brace roots’ frequently develop on the lower aerial nodes of the stem. On reaching the soil, they branch out and take part in the nutrition of the maize plants, but their main function is preventing the plants from lodging.
Flower:
The distinguishing feature of maize is the separation of the sexes among its flowering structures, i.e. a monoecious plant. Maize produces male inflorescences (tassels) which crown the plant at the stem apex, and female inflorescences (cobs or ears), which are borne at the apex of condensed, lateral branches protruding from leaf axils.
The male (staminate) inflorescence, a loose panicle, produces pairs of free spikelets each enclosing a fertile and a sterile floret. The female (pistillate) inflorescence, a spike, produces pairs of spikelets on the surface of a highly condensed rachis (central axis, or “cob”). Each of the female spikelets encloses two fertile florets, one of whose ovaries will mature into a maize kernel once sexually fertilized by wind-blown pollen.
Maize Grain:
The maize grain is botanically a caryopsis, a dry fruit containing a single seed fused to the inner tissues of the fruit case. Seed contains a germ from which a new plant will develop,
and an endosperm which will provide nutrients for that germinating seedling until the seedling establishes sufficient leaf area to become autotroph. The germ consists of a miniature plant axis, including approximately five embryonic leaves, a radicle, from which the root system will develop, and an attached seed leaf (scutellum).
The germ is the source of maize “vegetable oil” (total oil content of maize grain is 4% by weight). The endosperm occupies about two thirds of a maize kernel’s volume and accounts for approximately 86% of its dry weight. The primary component of endosperm is starch, together with 10% bound protein (gluten), and this stored starch is the basis of the maize kernel’s nutritional uses. Whole, ground maize meal has an energetic value of 3,578 calories per kilogram.
Growth Stages of Maize:
A growing plant of maize passes through following growth stages:
(i) Emergence:
Coleoptile reaches the soil surface and exposure to sunlight causes elongation of the coleoptile and mesocotyl to stop. The growing point, located just above the mesocotyl, is about 0.75 inches below the soil surface. Embryonic leaves rapidly develop and grow through coleoptilar tip. Seminal root growth begins to slow and nodal roots are initiated at the crown.
(ii) Seedling Stage:
This is the sprouting stage, which comes about one week after sowing, and the plants contains about 2-4 leaves at this stage.
(iii) Grand Growth Stage:
This is knee high stage of plants, which comes around 35- 45 days after sowing. Plants need first top dressing of nitrogenous fertilizers and final mechanical or manual inter cultivation because if this operation is delayed by any day the leaves will be damaged.
(iv) Tasseling Stage:
This is in fact a flower initiation stage at which the tassels or male flowers come out. This stage begins about 2-3 days before silk emergence. The plant is almost at its full height and pollen shed (anthesis) begins. Plants at this stage are most vulnerable to moisture stress and leaf loss. Final top dressing should be done at this stage.
Fertilizer application after this stage does not give any positive response.
(v) Silking Stage:
This is also known as cob initiation stage at which the female flowers or cobs are formed. This stage begins when any silk is visible outside the husk. These are auxiliary flowers unlike tassels that are terminal ones. Usually they are formed in the axis of 11th to 13th leaf whereas male flowers or tassels are formed at the apex after the appearance of 14th or 15th leaves.
Falling pollen grains are captured by the silk and grow down the silk over a 24 hour period ultimately fertilizing the ovule. The ovule becomes a kernel. The number of fertilized ovules is determined at this stage.
(vi) Milky Stage:
It begins when pollination and fertilization is over. Kernels are yellow on the outside with a milky white inner fluid. Kernels are in a rapid rate of dry matter accumulation and are approximately 80% moisture. This stage may be guessed by seeing the silks on the top of the cob which remains partially green or brown at this stage and the covering of the cobs also remain green.
(vii) Dough Stage:
At about 24-28 days after silking, the fluid in the endosperm has thickened to a pasty consistency due to the continued accumulation of starch. The cob appears white when kernels are removed, and kernels are about 70% moisture. This is the best stage for using green cobs for table purposes.
(viii) Physiological Maturity:
Occurring approximately 55-65 days after silking, all kernels on the ears have attained maximum dry weight. A black or brown layer has formed where the kernel attaches to the cob, indicating physiological maturity has been attained.
The stalk of the plant may remain green, but leaf and husk tissue has lost its green colour at this stage. Kernel moisture content ranges from 30-35% at this stage depending upon the variety and environmental conditions.
Classification of Maize:
Maize is an annual C4 plant, classified into 7 groups by Sturtevant (1899) based on the endosperm of kernels.
1. Dent Corn (Zea Mays Indentata Sturt):
This is the most common type of maize grown in USA, Northern Mexico, Canada, Australia and South Africa. Depression or dent in the crown of seed is the main characteristics of this type of corn which is the result of rapid drying and shrinkage of the soft starch.
2. Flint Corn (Zea Mays Indurata Sturt):
It is grown in Europe, Asia, Central and South America as well as it is principal type of grain corn grown in India. The endosperm in this type of maize kernel is soft and starchy in the center and completely enclosed by a very hard outer layer. The kernels are round on the top. The colour may be white or yellow. It is well adopted to poultry feeding.
3. Popcorn (Zea Mays Auerta Sturt):
Its cultivation is mainly confined to the New World, grown in small areas in many parts of USA. The size of kernel is small and the endosperm is hard. When they are heated (at 170°C), the pressure built up within the kernel suddenly results in an explosion and the grain is turned inside out. The grain is used for human consumption and is the basis of pop-corn confections.
4. Flour or Soft Corn (Zea Mays Amylacea Sturt):
It possesses a soft endosperm. Kernels are soft and of various colours, but white and blue are most common. They are like fruit kernels in shape. It is widely grown in the USA and South Africa.
5. Sweet Corn (Zea Mays Saccharata Sturt):
The sugar (20% on dry basis at green ear stage) and starch make the major component of the endosperm, which results in sweetish taste of the kernels before they attain the maturity. After maturity, the kernels become wrinkled. The cobs are picked up green (with 70% moisture) for canning and table purposes. The crop is mainly grown in Northern half of the USA and Canada. Yellow is predominant grain colour and are rich in Vitamin A and C.
6. Pod Corn (Zea Mays Tunicata Sturt):
Each kernel is enclosed in pod or husk in an ear which is enclosed in husks like other types of com. It is a primitive type of com not grown commercially.
7. Waxy Corn (Zea Mays Ceretina Kulesh):
Kernels have waxy appearance. Starch is entirely composed of amylopectin in contrast to common dent corn starch with 78% amylopectin and 22% amylose. Waxy corns are of Chinese origin. The mutations of dent corn have resulted in evolution of waxy com in USA. The waxy com hybrids developed in USA with starch similar to tapioca are grown for supplying raw materials for speciality products of the wet milling starch industry for textile and paper sizing and corn oil.
Uses of Maize:
Maize has a wide variety of uses which may be summarized as follows:
i. Animal Feed:
The bulk of the world’s corn production (as much as 75-90 per cent) is used for feeding animals. In the United States, approximately 40 per cent of the corn is used to feed hogs or pigs, 25 per cent for cattle, 15 per cent for poultry and 10 per cent for horses and sheep.
In the Corn Belt, hogs were traditionally turned loose in the corn fields so that they ‘hog down the corn’, thus saving the labour of harvesting the crop. Cattle are also brought from western U.S.A. to be fattened in the Corn Belt before they are slaughtered. Large numbers of poultry, horses, mules, sheep and other domestic animals are also fed on corn and its milled by-products.
Cornstalks, leaves, and sometimes green maize are stored in winter months and used as fodder or silage for dairy cattle. Corn is exported to many other countries, especially Japan and European countries for animal feeding. Corn grown in north-west Europe rarely reaches maturity but is used as a green fodder or winter feed as silage.
ii. Human Food:
In many parts of the world, especially in southern U.S.A., in Central and South America, Africa, southern Europe and some poorer Asian countries, maize is consumed as a food grain. The American Indians, the Mexicans and many African peoples use maize as a staple food. It may be consumed fresh, ground, boiled or mixed with other foods.
The south Europeans use maizemeal to make polenta; the Mexicans make corncakes or tortillas while Africans, particularly in South Africa, grind the grain to make pasty mealies. In the United States, many large firms prepare a wide range of corn products including cornflakes, corn syrup, grits, hominy, blancmange or cornflour and custard powder. Though it does not make good bread, its high yield and high food value make corn a supplementary food in many less favoured parts of the world where other cereals cannot be grown.
iii. Industrial Products:
From the harvested maize industrial alcohol can be made. After wet milling, starch can be obtained and maize is a major source of vegetable oil. The maize stalks are used in the manufacture of rayon, plastics, paper and wall-boards. In the United States thick corn cobs are manufactured into corncob pipes, especially in the state of Missouri.
Pulverized corn cobs are made into a kind of mild abrasive for removing the carbon from aeroplane engines. Elsewhere the cobs are burnt as a domestic fuel, or returned to the soil as an organic manure.