Performance of Testcrosses of S1 Lines Derived from Different Selection Cycles of Tropical Maize Reciprocal Composites.

Two late-maturing (Zea mays L.) maize complementary composites, TZL COMP3 and TZL COMP4, were formed following a comprehensive breeding system. These populations were subjected to four cycles of reciprocal recurrent selection for grain yield, resistance to foliar diseases and other desirable traits. A total of 100 inter-population testcrosses of randomly selected S₁ lines from the original (C₀) and improved (C₄) selection cycles of the composites were evaluated at four locations in Nigeria to assess progress in genetic gain from selection. The observed response to selection per cycle was 4 % in grain yield, -3 % in anthesis-silking interval, -2 % in southern leaf rust and -4 % in southern leaf blight. Improvement per cycle was -1 % in days to anthesis, -1 % in days to silking and -2 % in ear aspect. The genetic correlation showed that selection for increased grain yield was accompanied by increased days to anthesis and silking, plant height, ear placement, and ears per plant and a short anthesis-silking interval, resistance to southern leaf blight and better ear and plant aspect scores. S₁ lines derived from C₄ of the two composites produced the largest number of high yielding testcrosses. Mean grain yields of C₄ x C₄ testcrosses exceeded that of a commercial single cross hybrid by 13.9 %. The average of these testcrosses was also comparable to that of the commercial hybrid for other agronomic traits and resistance to foliar diseases. Although, the genetic variance in C₀ was larger than that of C₄, there was significant genetic variance among testcrosses in C₄. These results indicate that reciprocal recurrent selection was effective in improving grain yield and other traits of inter-population testcrosses without a loss in genetic variance.

Keywords: Reciprocal recurrent selection, Testcross performance, Late-maturing maize composites.