Comparison of Selection for S2 Progeny vs. Testcross Performance for Population Improvement in Maize
- E. S. Horner ,
- E. Magloire and
- J. A. Morera
Several methods of population improvement in maize (Zea mays L.) are available, but more information is needed to enable breeders to make the best choice among them. This study was conducted to compare selection among S2 progenies (S2 method) with selection based on testcross performance using inbred testers (TC method) in two populations, FS8A and FS8B. For the TC method, a line from FS8A was the tester used to evaluate S2 lines from FS8B and vice versa. Four cycles of selection were completed, and the selected populations were evaluated over a 4-yr period. Testing was done at two locations near Gainesville, FL, during both the selection and the evaluation phases. Gains in average combining ability over both populations and all tests were 4.7 and 3.0% cycle−1 for the TC and S2 methods, respectively (significantly different at P = 0.01). Linear regression based on these mean values accounted for 99% of the variation among cycles for each method. The TC method also produced higher predicted yields of populations per se (F = 0) in Cycle 4 (6.85 vs. 6.01 Mg ha−1). On the other hand, the S2 method resulted in a lower rate of yield depression in Cycle 4 for each 1% increase in inbreeding (0.04 vs. 0.06 Mg ha−) and in higher predicted yields of inbred (F = 1) populations (1.70 vs. 0.87 Mg ha−1). These results suggest that nonadditive gene action in the overdominance range is important in these populations because, in the absence of overdominance, the S2 method is expected to be the better procedure.
Copyright © 1989.