Maize (Zea mays L.) is the world’s leading crop and is widely cultivated as cereal grain that was domesticated in Central America. It is one of the most versatile emerging crops having wider adaptability. Globally, maize is known as queen of cereals because of its highest genetic yield potential. Maize is the only food cereal crop that can be grown in diverse seasons, ecologies and uses. Beside this maize have many types like normal yellow/ white grain, sweet corn, baby corn, popcorn, waxy corn, high amylase corn, high oil corn, quality protein maize, etc. Apart from this, maize is an important industrial raw material and provides large opportunity for value addition.
2. Taxonomy, Origin and Evolution Taxonomy
Maize belongs to the tribe Maydeae of the grass family Poaceae. “Zea” was derived from an old Greek name for a food grass. The genus Zea consists of four species of which Zea mays L. is economically important. The other Zea sp., referred to as teosinte, is largely wild grass native to Mexico and Central America. The number of chromosomes in Zea mays is 2 n = 20. Tribe Maydeae comprises seven genera which are recognized, namely Old and New World groups. Old World comprises Coix (2n = 10/20), Chionachne (2n = 20), Sclerachne (2n = 20), Trilobachne (2n = 20) and Polytoca (2n = 20), and New World group has Zea and Tripsacum. It is generally agreed that maize phylogeny was largely determined by the American genera Zea and Tripsacum, however it is accepted that the genus Coix contributed to the phylogenetic development of the species Zea mays. Kingdom Plantae
- Division Magnoliophyta
- Class Liliopsida
- Order Poales
- Family Poaceae
- Genus Zea
- Species mays
The transformation of maize from teosinte involved evolutionary forces such as mutation, hybridization, genetic drift and selection aided by the activities of human beings, who selected useful variatnts out of large populations of teosinte and concentrated them into isolated evolutionary pools. This resulted in the differentiation of maize into large number of races. The races gradually got adapted to different agro-climatic regions in the America away from the centre of origin. On the basis of morphological data, several authors suggested that there has been extensive gene flow between maize and with no visible leaf collar are not included. For example, a plant with 3 collars would be called a V3 plant, however, there may be 6 leaves showing on the plant.
VE – 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 the coleoptilar tip. Seminal root growth begins to slow and nodal roots are initiated at the crown. Weed control at this stage will result in little yield loss, but late-emerging weeds may produce substantial seed, increasing the soil seed bank.
V1 – First leaf collar
Lowermost leaf (short with rounded tip) has a visible leaf collar. Nodal roots begin elongation. Again, weed control at this growth stage will result in little yield loss, but seed from weeds that emerge later in the growing season may contribute to the soil seed bank if a residual herbicide has not been applied.
V3 – Third leaf collar
The growing point remains below the soil surface as little stalk elongation has occurred. Lateral roots begin to grow from the nodal roots and growth of the seminal root system has ceased. All leaves and ear shoots that the plant will produce are initiated at this stage. Since the growing point remains below the soil surface, cold soil temperatures may increase the time between leaf stages, increase the total number of leaves formed, delay tassel formation, and reduce nutrient uptake.
Environmental stress at this time is detrimental to pollination and seed set, with moisture stress causing desiccation of silks and pollen grains. Nutrient concentrations in the plant are highly correlated with final grain yield as nitrogen and phosphorous uptake are rapid.
R6 – Physiological Maturity
Occurring approximately 45-50 days after silking, all kernels on the ear 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, with much variation among hybrids and environmental conditions.