Genetic Analysis for Combining Ability and the Gene Action in Sunflower (Helianthus annuus L.) Using Half Diallel Cross

Abstract A field experiment was carried out in the right side of the Euphrates in Ramadi city Anbar province - Iraq, used in the research six pure varieties of Sun flower. These items introduced one-way half diallel in the 2018 spring season to produce 15 single crosses. The seeds of the parents and their hybrid were planted in the fall season 2018 in the design of R.C.B.D with three replicates. To estimate the effects of GCA, SCA and the gene action and some genetic parameters in the sun flower. The results showed that there were significant differences between the hybrids and its parents in all studied traits. Note that the GCA and SCA variation on the union was highly significant for all studied traits. It was found that the parent (5) is the best parent in terms of GCA in the individual plant yield, gave an effect of (8.83) while the hybrid (3 × 4) is the best hybrid in the effect of SCA for the weight of 1000 seeds and the individual plant yield, (28.84 and 28.46) respectively. While the highest value of the heterosis in the trait of the individual plant yield of the hybrid (4 × 6) gave a value of (57.29%). The GCA variance to SCA was less than one for all studied traits except plant height indicating that there is a dominance gene action controls heredity of traits. This was reflected in the increase in the degree of dominance of one for most of the studied traits. The percentage of inheritance in the broad sense ranged from (97.74%) for the individual plant status to (99.81%) for the number of seeds per disc, this is due to the high genetic variation and low environmental variability. The highest value of genetic improvement was given to the number of seeds disk with a value of 249.15. The new combinations can be used in the production of individual hybrids with high specific combining ability to produce high yields because most of their traits were controlled by the dominance gene.