ARS | Publication request: LINKAGE EQUILIBRIUM AMONG TIGHTLY LINKED RFLPS AND THE MS LOCUS IN OPEN-POLLINATED ONION POPULATIONS

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2002
Publication Date: November 15, 2002
Citation: Fuat Gokce, A., Havey, M.J. 2002. Linkage equilibrium among tightly linked rflps and the ms locus in open-pollinated onion populations. Hortscience.

Interpretive Summary: Hybrid-onion (Allium cepa L.) seed is produced using male sterilities conditioned by the cytoplasm of the female parent (CMS). The large-scale production of hybrid-onion seed is dependent on the availability of maintainer lines that are used to seed-propagate the male-sterile lines. In onion, it takes four to eight years to determine if maintainer lines can be selected from a population. We earlier developed molecular markers that distinguish onion cytoplasms, reducing from years to hours the time required to confidently identify cytoplasms. We also identified molecular markers flanking the gene in the nuclear genome that controls male fertility (Ms). In order to test the usefulness of these nuclear markers to select maintainer lines, we determined the relationships among these molecular markers and Ms using plants randomly selected from three open-pollinated populations. For all three populations, the molecular markers and Ms were in linkage equilibrium, meaning that specific molecular markers could not predict the genotypes at Ms. Therefore these molecular markers can only be used to select maintainer lines after the breeder generates disequilibrium by crossing among individual plants. These results will allow onion breeders to correctly use these molecular markers to identify and select maintainer lines from families generated after crossing.

Technical Abstract: Hybrid-onion (Allium cepa L.) seed is produced using cytoplasmic-genic male sterilities (CMS). In onion, male sterility is conditioned by the male-sterile (S) cytoplasm and the homozygous recessive genotype at a nuclear male-fertility restoration locus (Ms). The large-scale production of hybrid-onion seed is dependent on the availability of maintainer lines (N msms) to seed-propagate the male-sterile (S msms) lines. N and S cytoplasms can be distinguished by mitochondrial and chloroplast polymorphisms. We identified molecular markers flanking the Ms locus, which can facilitate the maintainer development by allowing breeders to select plants carrying the recessive allele at Ms. We assessed linkage equilibrium among linked molecular markers and Ms using plants randomly selected from three open-pollinated populations. For all three populations, the molecular markers and Ms were in linkage equilibrium. This means that marker-facilitated selection of maintainer lines can only be used after the breeder generates linkage disequilibrium by crossing among individual plants.