Molecular tagging of male-fertility restoration locus and its selection in onion (Allium cepa L.)

Cytoplasmic-genic male sterility (CMS) is used to produce hybrid-onion seed. For the most widely used source of onion CMS, male sterility is conditioned by the interaction of the male-sterile (S) cytoplasm and the homozygous recessive genotype at a single nuclear male-fertility restoration locus (Ms ). Maintainer lines possess normal (N) male-fertile cytoplasm and are homozyous recessive at the Ms locus. It takes four to eight years to establish if maintainer lines can be extracted from an uncharacterized onion population. Polymorphisms distinguishing N and S cytoplasms of onion have been identified and significantly reduce the time required to establish the cytoplasms of single plants. Segregations of restriction fragment length polymorphisms (RFLPs) revealed RFLPs flanking the Ms locus at 0.9 and 8.6 cM. The RFLPs and Ms were at or near linkage equilibrium in three open-pollinated onion populations.; Using the cDNA sequence (AOB272) revealing the most closely linked RFLP, we designed oligonucleotides and used the polymerase chain reaction to amplify genomic DNAs from seven commercial onion cultivars and the parents (Ailsa Craig 43 and Brigham Yellow Globe 15–23) of our mapping family. We cloned and sequenced these amplified genomic DNAs to identify single nucleotide polymorphisms (SNP). Oligonucleotides were designed flanking the SNPs and were used as allele-specific primers to distinguish genotypes in the AOB272 genomic region. These organellar and nuclear markers can be used to select maintainer genotypes from onion populations or segregating families and should reduce the number of testcrosses required to identify maintaining genotypes.; The bulb onion is a diploid species with natural outcrossing rates ranging between 70% to 100% in the field. Male sterile plants must receive the male gametes from male-fertile plants in order to set seed. Therefore, the frequency of the ms allele will change over generations due to natural selection of male gametes on male-sterile (S-museums) plants in onion populations possessing S cytoplasm or mixtures of N and S cytoplasms. I developed a model to predict changes in allied frequencies due to failure of male gamete production from S-museums genotypic plants in onion.