Study of microspore-culture responsiveness in oilseed rape (Brassica napus L.) by comparative mapping of a F2 population and two microspore-derived populations

RFLP segregation analyses were performed on a F₂ population and two F₁ microspore-derived populations from the same cross between a microspore culture-responsive parent (Topas) and a non-responsive parent (Westar). A total of 145 loci were detected with 87 cDNA clones. Eighty-two markers were common across all three populations. A total of 66 markers was assembled into 18 linkage groups and 16 markers remained unlinked. Segregation distortions were significant for 29% of the markers in the F₂ population and 23% and 31% in microspore-derived populations M3 and M5, respectively. An equivalent number of markers showed biased segregation towards each parental allele in the F₂ population while more markers showed a significant deviation from the expected Mendelian ratio towards the responsive parent in both microspore-derived populations. Different subsets of markers showed segregation distortions in the three populations indicating that the selective pressures leading to microsporederived plants are different from those acting during selfing of the F₁. Linkage groups 1 and 18 were identified as putative chromosomal regions associated with microspore-culture responsiveness.