CHAPTER ONE
INTRODUCTION
Maize belongs to the grass family of plants and its botanical name is Zea mays. It originated in South America and Central America, but its cultivation has today spread to nearly all parts of the world. It is grown through out the tropics and temperature region. (Onwueme, 1979).
Maize was introduced to West Africa by the Portuguese in the 16th century. It is a cercal crop that is grown widely throughout the world in a range of agro-ecological environments. (Onwueme, 1979).
About 50 species exists and consist of different colours, textures, shapes and sizes. White, Yellow varnishes are preferred by most people depending on the region. (IITA, 2009).
Maize was introduced into Africa in the 1500s and has since become one of African’s dominant food crops. Like many other regions, it is consumed as a vegetable although it is a grain crop. The grains are rich in dietary fibber and calories which are good source of energy. (IITA, 2009) and in vitamin A, C and E and essential minerals and contains 9% of protein.
Maize is the most important staple food for more than 1:2 billion people in SSA and Latin America (IITA, 2009).
The important of cercal grains to the nutrient of people around the world is widely recognized because they make up such a large part of duets in developing countries, cercal grains cannot be considered source of energy, as they provide significant amounts of protein as well. (FAO Corporate Document Repository). All part of the crop can be used for food and non food products. In industrialized countries, Maize is largest used live-stock feed and as raw materials for industrial products.
Maize accounts for 30-50% of low income house hold expenditures in Eastern and Southern Africa. A heavy relevance on maize in the diet however can lead to malnutrition and vitamin deficiency disease such as might blindness and Kwashiorkor.
Maize is processed and prepared in various forms depending on the country. Ground maize is prepared into porridge in Eastern and Southern Africa Ground maize is also feed or baked in many countries.(IITA 2009).
Worldwide consumption of maize is ore than 116 million tons with Africa consumption 30% and SSA 21%]. However, Lesotho has largest consumption per Capital with 174kg per year. Eastern and Southern Africa uses 85% of its produce as food while Africa as a whole uses 95%; compared to other regions of the world that use most of its maize consumption is in Africa and central America. It fetches premium prices in South America where it represents the main staple food. Yellow maize is preferred in most parts of South America and Caribbean. It is also the preferred animal feed in many regions as it gives a yellow colour to poultry egg yolks and animal fat.In all parts of Africa, green (fresh) maize is boiled or roasted on its cob and served as a snack popcorn is also a popular Snack (IITA, 2009).
The maize grain contains on the average 60% starch, 13% water, 10% protein, 4% oil, 2% Sugars and 3% fibre. Yellow maize contains appreciable amounts of vitamin A. (Onwueme, 1979).
Many studies have been conducted to understand and evaluate the effects of the genetic make up of the relatively large number of available maize varieties on chemical composition, as well as the effect of environment factors and agronomic practice on the chemical constituents and nutritive value of its kernel and its anatomical parts. Chemical composition after processing for consumption is an important aspect of nutritional value.
There are important differences in the chemical composition of main parts of the maize kernel. The seed coat/pericarp is characterized by a high crude fibre content of about 87% which constitute mainly of hemicelluloses (67%), cellulose (23%) and Lignin (0.1).
(Burge and Duensing 1989). On the other hand the endosperm contains a high level of starch (876%) and protein levels of about 8%. Crude fat content in the endosperm is relatively low. The germ is characterized by high crude fat content averaging about 33%. The germ also contains are relatively high level of protein (18.4%) and minerals.
The 92 percent of protein in teosinte comes from the endosperm. Protein in maize kernel has been reported on by a number of researcher (e.g Bressani & Mertz, 1958).
From the data above it is evident that carbohydrate and protein contents of maize kernel depend to a very large extent in the endosperm and crude fat and to a lesser extent protein and minerals on the germ.
Crude fibre in kernel comes mainly from the seed coat. The weight distribution among parts of the kernel and their particular chemical composition and nutritive value are of great importance’s. Germ oils provides relatively high level of fatty acids (Bressani et al.,).
The major chemical component of the maize kernel is stand, which provide up to 72 to 73 percent of the kernel weight. The starch is made up of two glucose polymers; amylase and amyl-pectin, a branched form. The composition of maize starch is genetically controlled. (Boyer and Shannon, 1987).
After starch, the next largest chemical component of the kernel is protein. Protein content varies in common varieties from about 8 to 11 percent of the kernel weight. The protein in maize kernels has been studied extensively. It is made up of at least five different fractions, according to (Landry and Moureaux 1970, 1982)
The oil content of maize kernel is genetically controled with values ranging from 3 to 18 percent. It may be expected that oils from different varieties have different composition. Maize oil has a low level of saturated fatly acids. It contains on the other hand relatively high level of polyunsaturated fatty acids. (Bressani et al., 1990).
After carbohydrates, proteins and fats, dietary fibre is the chemical component found in the greatest amounts. (Sandstead et al., 1978) found that maize bran was composed of 75 percent hemicelluloses, 25 percent cellulose and 0.1 percent lignin on a dry-weight basis.
The maize kernel contain two fat-soluble vitamins provitamin A, or carotenoids and vitamin E.
Carotenoids are found mainly in yellow maize, in amounts that may be genetically controlled, white maize has little or no caroteniod content. But unfortunately yellow maize is not consumed by humans as much as white maize (Squibb,et al., 1957) found beta-carotene to be about 22 percent of total carotenoids (6.4 to 11.3 pg per grain) in yellow maize samples.
The water-soluble vitamin nicotinic acid has attracted much research because of its association with niacin deficiency or pellagra, which is prevalent in populations consuming high amounts of maize (Christianson et al., 1968).
Maize has no vitamin B12, and the mature kernel contains only small amounts of as corbie acid, if any (Yen, et al .,1976) reported a content of about 2.69 mg Per kg of available pyridoxine. Other vitamins such as folic acid, choline and pantothemic acid are found in very low concentrations.
The need for high protein maize i.e. quality protein maize which contains nearly twice as much usable protein as other maize grown in the tropics and yields 10% more grain than traditional varieties of maize was developed by Dr. Surinder Vasal and Dr. Erangelona Villeg as at the International Maize and wheat improvement center (CIMMYT) in the late 1990s.
In central and South America, Africa and Asia, several hundred million people rely on maize as their principal daily food, for weaning babies and feeding livestock.
Unfortunately maize has two flaws, it lacks the full range of amino acids, namely lysine and tryptophan needed to produce proteins and has its niacin (vitamin B3) a bound in an indigestible complex.
Thus, conventional maize is a poor quality food staple: unless consumed as part of a varied diet which beyond the means of most people in developing world.
Quality protein maize produces 70-100% more lysine and tryptophan than the most varieties of tropical maize. This two amino acids allow the body to manufacture complete protein thereby eliminating wet-mal nutrition. In addition tryptophan can be converted in the body to Niacin which theoretically reduces the incidence of pellagra (Palit et al., 2003).
Induce mutation breeding which has been recognized as a valuable supplement to conventional breeding in crop improvement has been least applied in cereals.
Mutations are changes to the base pair sequence of the genetic materials of an organism. Normally, genes replicate and chromosomes segregate with times without an error. Variation occur when new gene combinations are established in sexual reproduction, but the individual genes remain unchanged.(Cassandra 2008).
From time to time however, an organism may appear with characteristics totally unlike any of either parent but transmitted to the next off spring. As the trend continues, it represents a sudden genetic change rather than an environmental influence. Such changes are referred to as mutation and the organism possessing it as mutant.
Mutation creates a variation in gene pool and less favourable mutation are reduced in frequency in the gene pool by natural selection, while more favourable (beneficial) mutations tend to accumulate resulting in evolutionary changes.
Mutation can be caused by copying errors in the genetic material during cell division, exposure to wba-violet or lionizing radiation, chemical mutagens environmental mutagens e.g Ultra-violet rays from sun cigarette smoke, high energy radiation such as X-rays, viruses or can occur deliberately under cellular control, under processes such as hyper-mutation. (Griffith et al., 2000).
In multicultural organisms, mutation can be subdivided into gremlin mutation which can be passed to descend ant in mammals (Cassandra, 2008). Plants sometimes can transmit mutation to their descendant, in cases in where the lower buds develop in somatically mutated parts of plants (Cassandra, 2008). Plants sometimes can transmit mutated part of plants, if desirable may be budded into rooted stems and propagated as a bud mutant (O Ho and Towle, 1976).
Mutation induction is the starting step in mutation breeding. It is characterized by the generation of new alleles as its most unique features (Shu, 2009).
In classical mutation breeding, induced mutations are embedded in mutants that are either directly or indirectly (through crosses with other varieties) used for developing new variety, whereby. It is rather difficult to trace the mutated genes in subsequent breeding (Shu, 2009).
By inducing mutation in maize, it may be possible to identify new genes and this broaden the spectrum of inheritable changes and expand maize germ plasm.
Using mutants in cross breeding requires no in depth knowledge about mutations, because the mutated traits is the object of desire. But when mutant trait is not expected the breeder may begin to think about the actual mutational event, that led to the mutant phenotype.
Mutation is induced to keep desirable qualitative characteristics in a more stabilized manner (Otto and Towle, 1976).
It should be noted that breeding was practiced involving the crossing of characters of not one or two put hundred characteristics white the law of hereditary applies, the results are not always as predictable as they wherefore Mendel’s serve traits in garden pea; PisumSativum (Otto and Towles, 1978).
In 1928, Herman J. Muller devised a method of searching for a lethal mutation on the X chromosome in Drosophila and this led to the first experimental evidence of mutagen. Mutagens have been available tool, not only for studying the mechanism of mutation itself but also for invocating the yield of mutants for other genetic studies (Griffith et al., 2000).
Since the discovery of experimental mutagenesis in the early 20th century a wide array of mutagens have been explored, from physical mutagens such as cosmic radiation, radiation from X-ray macaroni, radio ative fallout etc. e.g mustard gas to chemical mutagen led to environmental pollutants. E.g cigarette smoke to synthetic chemical like NaH3, EMS, MMS etc. to even natural chemical mutagens in our food. [ Griffith et al., 2000).
Interestingly, certain vegetable oils that we consume daily have been documented to be highly potent in inducing mutation such as chromosome aberration and spindle fibre disruption in wheat (Natarajan, 2005)
A number of national, provincial and regional research institutes and universities have been involved in crop improvement using mutation techniques and significant achievements are made from early stages (Wang 1985, 1992) till very recently. (Liu et al 2004)
However, information in chemical composition mutations in maize is very limited. Thus, this study aims to induce mutation in maize using natural mutagens. This hope that the hazardous practice of the use of irradiation and chemicals which are carcinogenesis, soil pollutant, non-biodegradable etc. will in turn be curbed.