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.