Response to 13 cycles of reciprocal full-sib recurrent selection in the BS10 and BS11 maize (Zea mays L) populations
The goal of reciprocal full-sib recurrent selection (FR) is the improvement of the cross between two populations for selected characters by increasing the frequencies of favorable alleles, while maintaining genetic variability for continued improvement. FR was initiated in BS10 and BS11 prolific maize populations in 1963, a program currently in its 15th cycle of selection. The objectives of this study, therefore, include the evaluation of long-term direct and indirect selection effects on the BS10/BS11 population cross and BS10 and BS11 per se populations, respectively, over the first 13 cycles of selection. Also assessed are effects of selection on heterosis and inbreeding depression in the two populations, and the impact of FR on genetic variation and heritability in the parent populations.;Thirteen cycles of FR have been successful in improving BS10/BS11 for grain yield and moisture, stalk lodging, plant and ear height, and number of days to mid-anthesis and mid-silk. Indirect effects of selection on the per se populations include significant improvements for grain yield and stalk lodging in BS10 and grain yield and moisture, plant and ear height, and days to mid-anthesis and mid-silk in BS11. Increases in grain yield, the primary trait for selection, include a direct response of 2.2 percent per cycle in the population cross, and indirect responses of 3.3 and 1.2 percent per cycle in BS10 and BS11, respectively, but only the response for BS11 fits a linear model. Linear trends through the first nine selection cycles, however, indicate a 4.6 percent per cycle increase for the population cross, as well as increases of 1.6 percent in BS10 and 1.6 percent in BS11 parent populations.;Evaluations of random S1 line performance for BS10C0, BS10C13, BS11C0, and BS11C13 indicate decreasing trends in genetic variability over 13 cycles of FR. Exceptions are grain yield in BS10 and BS11 and plant height in BS11. While genetic variance estimates for grain yield are nearly equal for BS11C0 and BS11C13, a nearly significant increase invariability is evident from BS10C0 to BS10C13. Variability estimates suggest FR for grain yield in BS10 and BS11 will be effective in future selection cycles.