Molecular Markers Assisted Selection Of A Dominant Male Sterility Gene In Cabbage(Brassica Oleracea Var. Capitata)

Cabbage (Brassica oleracea var. capitata) is a worldwide vegetable crop belonging to the Cruciferae family. Utilization of male sterile lines is of significant importance for hybrid seed production. A dominant male sterility gene (Ms) was identified from a spontaneous mutation in a spring cabbage line 79-399-3. As this Ms gene has been used in hybrid seed production of several Brassica oleracea cultivars, to further accelerate the application of this male sterility, this present research aimed to advance further research in the aspect of molecular marker assisted selection.One of the most important key steps for the utilization of dominant male sterility in cabbage is to identify plants with homozygous dominant male sterility genotype. AFLP technology was applied to marker-assisted selection in two near isogenic populations, 03A and 03B. After screening their corresponding genotypes MsMs, Msms and msms of the two sets of near isogenic lines, we developed, respective to each line, two sets of AFLP markers (5 markers for each set) which can be used for identifying cabbage plants with homozygous dominant male sterility genotype. These markers can be used to identify homozygous dominant male sterility genotype by selecting plants which the markers are absent, as all of them are linked in repulsion to the dominant Ms gene. Among these AFLP markers, e33m52 is applicable for selecting plants with homozygous dominant male sterility gene locus in both 03A and 03B populations. Using genomic PCR walking, e33m52 was successfully converted into a SCAR (Sequence Characterized Amplified Region) marker, which can be used directly and is much more efficient in practical utility. As a 9 generations backcrossed NIL population with 25 individuals has been used for identifying the marker, predicted precision was 96%. In the present research, polymorphism was analyzed in 64 cabbage accessions by using the 5 AFLP markers selected from 03B to determine the practical limitation of each marker.AFLP technology was applied to the analysis of a segregating BC8 population with 95 individuals. In total, 11 AFLP markers out of 512 primer combinations were identified, which were e36m73, e35m80, e36m75, e32m67, e38m55, e32m71, e37m31, e37m75, e36m58, e37m72 and e37m44. Determined by Joinmap 3.0, these markers were all linked to Ms locus from the same side. Among these markers, e36m73, the nearest one, located 1 cM from the Ms gene, while, e37m44, the most distant one, was 21 cM from the gene. The largest interval distance between linked markers was 7 (7.70 ) cM, and the nearest one was 1 (0.562) cM.After analyzing all polymorphic markers, we obtained a linkage of 6 markers, covering 9 cM, which were not linked to the dominant male sterility gene. This clearly suggests that even in the advanced backcross generation, selection by only traditional methods cannot remove "genetic carry-over". The detection of "genetic carry-over" in the BC8 suggests that molecular marker assisted genetic background selection at the earlier generations is important in an efficient breeding program.