Combining ability of maize inbred lines from four cycles of recurrent selection

The goal of recurrent selection is to improve population performance while maintaining genetic variability. In maize (Zea mays L.), this genetic improvement should lead to improved performance of hybrids derived from the improved population. Inbred lines from four cycles (C); C0, C1, C3, and C4 of S₁ and testcross selection for grain yield in a maize population (Tennessee Late Low-ear synthetic) were crossed to three testers to determine whether improvements in population performance resulted in improved performance of lines selected from the population. A minimum of seven lines from each cycle X selection method group was crossed to inbred lines 373, T220, and T165. Hybrids were evaluated at two locations for two years. From S₁selection, Cl hybrids had significantly better combining ability for grain yield than C0 hybrids (10.01 vs 9.49 Mg ha⁻¹), but yield of C3 and C4 hybrids did not differ from C1. Combining ability for grain yields of hybrids from testcross selection were lower than for S₁ selection in Cl and C3. The C4 hybrids from testcross selection were significantly higher yielding than the C3 hybrids (9.97 ys 9.66 Mg ha⁻¹). There was no difference between selection methods in combining ability of C4 hybrids. In both testcross and S₁ selection grain moisture, erect plantS₁ and plant height decreased from C0 to C4. Ear height increased from C0 to C1 and decreased in C4 of S₁ selection to a lower placement than C0, whereas ear height in C4 of testcross selection had a decrease, but the hybrids still had a higher ear placement than C0. The increase in combining ability of lines was less than the response to selection observed in the random mating population.