Minufiya J. Agric. Res. Vol. 38 No. 1(1): 109: 125 (2013) "http://WWW.mujar.net" 90) COMBINING ABILITY, HETEROSIS AND ASSESSING GENETIC DIVERSITY USING RAPD MARKER IN MAIZE A.A.A. EL-Hosary (1) and A. A. Elgammaal (2) (1) Department of Agronomy, Faculty of Agriculture, Benha University, Egypt. (2) Department of Agronomy, Faculty of Agriculture, Tanta University, Egypt. (Received: Dec. 13, 2012) ABSTRACT: A half diallel cross between seven inbred lines of maize were evaluated under two different sowing datess for grain yield and its components i.e. No. of rows ear, No. of kernels row, 100-kernel weight and grain yield/ plant. The results showed that the mean squares for sowing dates, genotypes, parental inbred lines, crosses and parent vs crosses were found to be highly significant for all traits studied. The crosses P 3 xP 5 , P 4 xP 5 , P 4 xP 7 , P 5 xP 7 and P 6 xP 7 in early sowing dates, P 5 xP 7 in late sowing dates and P 4 xP 5 , P 4 xP 7 and P 5 xP 7 in the combined analysis, had significant out yielded (heterosis) than the best check hybrid (SC Pioneer 30k8). The mean squares associated with general and specific combining abilities were significant for all traits. GCA/SCA ratio was less the unity for all traits except no. of rows ear -1 , indicating that greatest role of the non-additive type of gene action in the expression of these traits. The parental inbred lines P 4 and P 7 seemed to be the best general combiners for grain yield plant -1 and some of its components in the combined analysis of both sowing datess. The parental combinations P 3 xP 5 , P 4 xP 5 , P 4 xP 6 , P 5 xP 6 , P 5 xP 7 , P 1 xP 4 and P 2 xP 4 had the best SCA effects for grain yield plant -1 in the combined analysis. The genetic diversity (GD) among seven parental inbred lines was investigated using Random Amplified Polymorphic DNA (RAPD). The genetic diversity among the seven parental inbred lines ranged from 0.19 to 0.49. The correlation between GD and mean performance for grain yield which computed for 21 hybrids combination were found to be positive values (r = 0.07). Therefore, this specified tendency could be predicted about the relationship of GD for grain yield plant-1 in this study. We recommended that the hybrid P5xP7 could be used in the programs maize hybrid production. RAPD marker can be used as a tool for determining fingerprint for each line and the extent of genetic diversity among maize inbred lines and for genotypes into different groups but when used a large number of primers to detect the variation over all DNA or used a new marker like SSR or AFLP. Key words: Maize, Heterosis, Combining ability, additive, sowing date, RAPD, Genetic diversity. INTRODUCTION To establish a sound basis for any breeding program, aimed at achieving high yield, breeders must have information on the nature of combining ability of parents, their behavior and hybrid combination performance (Chawla and Gupta, 1984). Diallel analysis technique is the choice of providing such detailed genetic information for selecting breeding materials that show great promise for success (Lonnquit and Gardner, 1961). The genetic parameter general combining ability (GCA) and specific combining ability (SCA) were defined by Sprague and tatum, (1942). Both GCA and SCA effects should be taken into consideration when planning maize breeding programs to produce and release new inbred lines and crosses. Furthermore, the magnitude of genetic components for a certain trait would depend mainly upon the environmental changed under which the breeding genotypes will be tested. In this respect, many researchers (EL-Hosary et al. 2006; Sedhom et al. 2007; Ngaboyisonga et al. 2009; Hefny 2010 and Irshad-El-Haq et al. 2010) concluded that the additive genetic (GCA) variance was more affected by environmental changed than the non- additive (SCA) variance for grain yield plant -1 .