COMPARING CONVENTIONAL EARLY GENERATION SELECTION WITH MOLECULAR MARKER ASSISTED SELECTION IN MAIZE

To be useful to plant breeders, gains made from molecular marker-assis ted selection (MAS) must be more cost-effective than gains made throug h traditional breeding. The objective of this research was to evaluate the effectiveness of MAS in an applied maize (Zea mays L.) breeding p rogram. Maize population BS11 (FR) C-7 was chosen to improve hybrid FR Mo17 x FRB73. FRMo17 and BS11 were crossed, then random-mated to creat e Fz plants (families). F-2 plants were testcrossed to FRB73 and genot yped with 34 molecular markers. F-2 families were selfed to create F-2 :S-4 families. Based on F-2 testcross yield, the top 20 families were selected. A second set of 20 families was selected based on a marker-d erived selection index. Marker genotypes were obtained for 20 plants w ithin each of the marker selected families. Index selections were made for favorable and unfavorable genotypes within the 20 families. F-2:S -4 testcrosses to FRB73 were grown to compare the different selection methods. Selection among F-2:S-4 families using either method resulted in similar testcross performance. However, neither method selected fa milies that performed significantly better than FRMo17 x FRB73 or the S-0 unselected population testcross. Within-family index selection was not effective. The selection index, developed with F-2 testcross data , was not correlated with F-2: S-4 testcross performance. Marker-yield associations were determined using F-2:S-4 genotypic and testcross pe rformance data. Ten (31%) markers were significantly associated with y ield. One marker-allele combination was favorable (and significant) in both F-2 and F-2:S-4 testcross performance.