Estimation of Combining Ability and Gene Effects in Forage Maize(Zea mays L.) Using Line × Tester Crosses

Determination of gene effects and combining abilities is regarded as a critical stage in the improvement of corn inbred lines. In the present study 20 S6 lines as female and three S6 commercial inbred lines (K18, K19, K1264/5-1) as tester were crossed and the resulting test cross progenies were evaluated in a randomized complete block design with three replications in 2008. During the growing priod, several agronomic characters including forage yield were measured. Effects of lines and testers were significant on all characters except for ASI and days to physiological maturity for lines and ASI for testers. This indicated the existence of additive genetic variance for most of the traits under investigation. Inbred lines L5, L14 and L1 were good general combiners for forage yield because they showed significant positive GCA for this trait. L14 was superior over L1 and L5 because of significant positive GCA for most of the agronomic characters Thus, these lines, especially L14, have potential additive genes to be utilized in the breeding programs. T3 tester had favorable additive genes for forage yield, its components, early maturity and shorter stature. The highest forage yield (79.040 t/ha) with large positive SCA belonged to L5 × T3 combination. L2 × T3 and L15 × T2 were regarded as other desirable combinations. Additive genetic variance was substantially larger than dominance genetic variance for all of the traits except days to physiological maturity. This indicated that additive gene effects were more prominent than dominance effects in controlling forage yield and some other agronomic traits in relation to the studied S6 inbred lines. Therefore, narrow sense heritability estimates closely resembled the broad sense heritability values except for phenological characters. Medium to high narrow sense heritability estimates enable to select for favorable additive gene effects among the studied lines.