Diallel Cross Analysis for some White Maize Inbred Lines under Two Nitrogen Levels

A half diallel cross among seven white inbred lines of maize was made in 2016 growing season. The resulted of 28 F₁ crosses along with the check hybrid SC130 were evaluated under two different nitrogen levels, i.e., 90 and 120 kg N/ fed using a randomized complete block design (RCBD) with three replications at the Experimental Farm, Faculty of Agriculture, Kafrelsheikh University in 2017 growing season, to estimate general (GCA) and specific (SCA) combining ability effects and their interactions with nitrogen levels as well as identify type of gene action controlling the inheritance of the studied traits. Data were recorded on days to 50% silking, plant height, ear height, ear length, ear diameter, No. of rows/ear, No. of kernels/rowand grain yield (ard/fed). The results showed that, the mean squares due to nitrogen levels (D), genotypes (G), crosses (Cr.), G × N and Cr. × N interactions were significant for all the studied traits. General (GCA) and specific (SCA) combining ability mean squares were highly significant for all the studied traits under both and across nitrogen levels. Both GCA and SCA effects were significantly interacted with nitrogen levels for all the studied traits, except GCA × N for ear diameter. The non-additive gene action played an important role in the inheritance of all the studied traits under the two nitrogen levels and the combined data, except days to 50% silking under N1 level. The inbred lines P₁ and P₇ showed the best desirable GCA effects for earliness and P₂ and P₆ for shorter plants and lower ear placement. Whereas, P_2, P₃ and P₄ were the best general combiners for grain yield. The crosses P₁×P₃, P₂×P₇, P₃×P₆, P₄×P₅ and P₅×P₇ had the best SCA effects for grain yield as well as one or more of its components under both and across nitrogen levels. The two crosses P₂×P₇ and P₄×P₅ exhibited significant and positive superiority over SC 130 under both and across nitrogen levels.