The introduction of hybrids was the most important advance in the cultivation of maize. The first commercial sale of hybrid seed started in 1984. Inbred lines of maize show general deterioration in yield and vigor, but hybrid between two inbreds immediately and completely recovers. In many cases, their yield exceeds that of the varieties from which inbred were derived (Shull,1908). Increased production per unit area is the primary objective in many maize-breeding programs. Of these, grain yield is the most important and complex character with which the maize breeders work. Maize displays an orderly sequence of development of yield components namely number of cobs plant-1, number of kernel rows cob-1 and kernel weight (Viola et al., 2003). To guarantee high yield of maize crop, farmers often grow improved varieties usually from different sources either alone or with other local varieties resulting in diversity among cultivars grown within and among farmers. Genetic variability, which is a heritable difference among cultivars, is required in an appreciable level within a population to facilitate and sustain an effective long term plant breeding programme. Progress from selection has been reported 340 Int. Res. J. Agric. Sci. Soil Sci. to be directly related to the magnitude of genetic variance in the population (Tabanao and Bernardo, 2005). Large amount of genetic variability has been observed to occur in the original accessions and races among sampled population representing different climatic and geographical regions ( Ilarslan et al., 2002). Abayi et al. (2004), Turi et al. (2007) and Salami et al. (2007) observed significant genetic variation in important agronomic traits, especially earliness to sufficiently justify the initiation of selection programme. Breeders have developed thousands of hybrids, of which one or more can flourish in almost any combination of soil and climate found in farming areas. Better uniformity of hybrids is useful for machine harvesting.