Development and characterization of microsatellite markers in the sexual-apomictic complex Taraxacum officinale (dandelion)

Microsatellite markers were developed in Taraxacum officinale to study gene flow between sexual and apomictic plants and to identify clones. Twenty five thousand genomic DNA clones were hybridized with a [(CT).sub.12] D probe. The density of [(GA/CT).sub.n] repeats was estimated at one every 61 kb in the T. officinale genome, which translates to 13 500 repeats per haploid genome. Ninety two percent of 110 positive clones sequenced contained at least one [(GA/CT).sub.n ≥ 5 repeat. Sixteen [(CA/GT).sub.n ≥ 5] and 11 [(AT).sub.n [greater than or equal to] 5] arrays were also found in these sequences, suggesting some clustering of dinucleotide repeats. Among 50 PCR primer pairs tested, 32 produced bands and 28 of them were polymorphic. Of these polymorphic markers, 15 were putatively single-locus and the other 13 produced only polymorphic fingerprints. Six loci were further characterized for polymorphism and showed between 6 and 32 alleles per locus. Among eight primer pairs used to analyze the progeny of a sexual cross, seven were co-dominant single-locus Mendelian markers, but one (MSTA10) gave a dominant pattern in accordance with the hypothesis of a null allele segregating in a Mendelian fashion. Three pairs of loci among 28 showed significant linkages of 10, 21, and 39 cM. Observed and expected heterozygosities in two sexual populations indicate that null alleles may be present at two loci, including MSTA10.