HETEROSIS, COMBINING ABILITY AND GENETIC PARAMETERS IN MAIZE

A field trial was carried out on the Field Crops Research Station of IPA in Abu Ghraib. Eight inbred lines of maize were used in this study using half diallel cross, in spring season of 2000, to produce twenty eight F1 crosses. The parents and crosses were grown in fall season of 2000 using RCBD with four replications to determine heterosis, general and specific combining ability effects and gene action. Highly significant differences were found among parental lines and their crosses for all traits the result were showed that the cross X Agr183 gave the highest cross vigor in each grain yield / plant (68.4%) and ear length (14.8%) of the mid - parent. While the cross Wc163 x W13R gave higher cross vigor in grain yield / plant (53.3%) of the better parent. The variance due to GCA and SCA were highly significant for all the traits studied except number of rows/ear where only GCA was significant. The parental line (Oh40) had the best GCA effects for yield and yield components. The parental line (HS) had the best GCA effects for plant and ear height. The highest SCA effects were expressed in Oh40 x Agr183 for grain yield, number of rows / ear and ear length. The variance ratio of GCA to SCA appeared less than one for all characters except weight, which was more than one indicating to be that these traits were controlled by dominance effects while the weight was controlled by additive effects. The values of dominance genetic variance were more than values of additive for all characters except the 50% date and weight, and this reflects the reduction of the values of the narrow sense heritability for all characters except the weight (55%), and the estimates of the average degree of dominance were exceeded one for all characters except the weight, which is an indications that heterosis for these characters due to dominant gene action. The results indicate that some inbred lines could be used in a breeding program to develop new versions of high yield per plant and SCA to produce better grain yield hybrids, and most studied traits were under dominance and over dominance gene action. This showed that developing elite hybrids were the best method for improving maize grain yield.