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

Abstract
Determination of gene effects and combining abilities is a critical stage in maize hybrid breeding. In the present study, 20 S₆ lines as female and three S₆ inbred lines (K18, K19 and 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 period, several agronomic characters including forage yield were measured. Effects of lines and testers were significant on all the characters except ASI and days to physiological maturity for lines and ASI for testers. This indicated the importance of additive gene effect in controlling most of the traits under investigation. Inbred lines L5, L14 and L1 were identified as good general combiners for forage yield because they showed significant positive GCA for this trait. L14 was superior compared with L1 and L5 because of significant positive GCA for most of the agronomic characters. These lines, especially L14, have potential additive gene effects to be utilized in the breeding programs. T3 tester showed favorable additive gene effects 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 crosses were other desirable combinations. Additive genetic variance was substantially higher 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.