Utilization of doubled haploid technique in Brassica rapa population improvement

The utilization of doubled haploid (DH) plants in population improvement of Brassica mpa was studied by randomly intercrossing 4, 8, 12 and 22 DH line s developed from the B. rapa cultivar Reward and the B. rapa breeding line DSC-3 for two generations to constitute synthetic populations. The syntheti c populations and the DH plants used in their formation were evaluated for agronomic performance at two locations in the field in 1996 and for genetic variation using random amplified polymorphic DNA (RAPD) analysis. Intercro ssing as few as four DH lines from the breeding line DSC-3 produced a synth etic population with improved performance over that of the contributing DH lines. The synthetic population produced from the interpollination of eight DH lines showed an agronomic performance over that of the contributing DH Lines to a level similar to the Reward donor population. RAPD analysis effi ciently characterized the genotypic variation present in DH lines and synth etic populations, detecting 22-72% polymorphism between DH lines, 17-53% an d 27-47% polymorphism in the first and second synthetic populations, respec tively. This characterization may be useful as a tool in the reestablishmen t of heterogeneity and recovery of agronomic performance in B. rapa synthet ic populations derived from DH lines by determining the level of genetic va riability among DH Lines and therefore optimal population size.