Effects of reciprocal full-sib selection in maize
Fifty full-sib families and 100 S(,1) lines were developed from randomly chosen parents in each of the maize (Zea mays L.) populations BS10C0, BS10(FR)C6, BS11C0, and BS11(FR)C6 to investigate the effects of six cycles of reciprocal full-sib selection on population means and variances. Progenies were evaluated in experiments at two Iowa locations in 1983 and 1984. Data were collected for grain yield, ears per plant, percentage of root and stalk lodged plants, date of 50% silk emergence, ear and plant height, and number of tassel branches;Significant increases in yield and ears per plant among full-sib families and S(,1) lines were detected from the C0 to C6 cycles of BS10 and BS11. At both inbreeding levels, population means were significantly reduced from the C0 to C6 cycles for percentage of stalk lodging in both populations, and for percentage of root lodging and silking date in BS11. Among full-sib families in BS10 and BS11 mean ear and plant height decreased from the C0 to C6 cycles. Increases in mean ear and plant height were observed among S(,1) lines from BS10C0 to BS10(FR)C6, while population means of these traits decreased significantly from BS11C0 to BS11(FR)C6. At both inbreeding levels, population means for number of tassel branches increased from BS10C0 to BS10(FR)C6 and decreased from BS11C0 to BS11(FR)C6;Inbreeding depression for most traits decreased in response to selection. Reductions were significant for ear and plant height in BS10, and for yield, silking date, plant height, and number of tassel branches in BS11;For most traits, magnitudes of variances among full-sib families and S(,1) lines responded similarly to reciprocal full-sib selection. Magnitudes of additive genetic variance tended to decrease from the C0 to C6 cycles of BS10 and BS11 for yield, percentage of stalk lodging, ear and plant height, and number of tassel branches and seemed to increase for ears per plant and percentage of root lodging from BS10C0 to BS10(FR)C6 and for plant height from BS11C0 to BS11(FR)C6. Estimates of dominance variance generally increased, but decreases were observed for percentage of root lodging in BS10 and for yield, percentage of stalk lodging, and plant height in BS11. If actual changes in genetic variances have occurred, they have been small. Several negative estimates of dominance, environments x additive, and environments x dominance variances were obtained.