To be useful to plant breeders, gains made from molecular marker‐assisted selection (MAS) must be more cost‐effective than gains made through traditional breeding. The objective of this research was to evaluate the effectiveness of MAS in an applied maize (Zea mays L.) breeding program. Maize population BS11 (FR) C7 was chosen to improve hybrid FRMo17 × FRB73. FRMo17 and BS11 were crossed, then random‐mated to create F2 plants (families). F2 plants were testcrossed to FRB73 and genotyped with 34 molecular markers. F2 families were selfed to create F2:S4 families. Based on F2 testcross yield, the top 20 families were selected. A second set of 20 families was selected based on a marker‐derived selection index. Marker genotypes were obtained for 20 plants within each of the marker selected families. Index selections were made for favorable and unfavorable genotypes within the 20 families. F2:S4 testcrosses to FRB73 were grown to compare the different selection methods. Selection among F2:S4 families using either method resulted in similar testcross performance. However, neither method selected families that performed significantly better than FRMo17 × FRB73 or the So unselected population testcross. Within‐family index selection was not effective. The selection index, developed with F2 testcross data, was not correlated with F2:S4 testcross performance. Marker‐yield associations were determined using F2:S4 genotypic and testcross performance data. Ten (31%) markers were significantly associated with yield. One marker‐allele combination was favorable (and significant) in both F2 and F2:S4 testcross performance.

Full‐sib selection is one method of intrapopulation improvement used in maize (Zea mays L.). This study was conducted to evaluate the progress from 10 cycles of full‐sib recurrent selection in the Nebraska Krug open‐pollinated maize population. A 2‐yr full‐sib selection cycle was applied to the Krug population beginning in 1966. The selection criterion was a multiplicative selection index consisting of yield (adjusted to 155 g kg−l moisture), proportion of standing plants, and proportion of plants without dropped ears. Based on field evaluations across nine seasons, the selection index increased 0.17 Mg ha−l cycle−1 (4.4% cycle−1), yield increased 0.07 Mg ha−l cycle−l (1.2% cycle−l), the proportion of standing plants increased 2.8% cycle−l, and the proportion of plants without dropped ears increased 0.1% cycle−l. Grain moisture at harvest decreased 3.0 g kg−l cycle−1 (0.3% cycle−1). Changes in plant traits other than those involved in the selection index were also measured. The multiplicative selection index was successful in increasing the yield on standing plants when applied to a full‐sib breeding system. Data indicate that yield on standing plants has continued to increase through the tenth cycle of selection.