Chromosomal location of a pollen fertility-restoring gene, Rf, for CMS in Japanese bunching onion (Allium fistulosum L.) possessing the cytoplasm of A. galanthum Kar. et Kir. revealed by genomic in situ hybridization

In a previous study, we developed cytoplasmic male sterile lines of Allium fistulosum possessing the cytoplasm of A. galanthum, a wild species, by continuous backcrossing. Furthermore, we reported the presence of a pollen fertility-restoring gene (Rf) for cytoplasmic male sterility (CMS) in A. fistulosum from segregation of pollen fertility of backcross progenies. In the present study, genomic in situ hybridization (GISH), using genomic DNA of A. galanthum as the probe DNA and that of A. fistulosum as the blocking DNA, was applied to F₁ hybrids between both species and backcross progenies to determine the chromosomal location of the Rf locus. By means of GISH, eight chromosomes from A. galanthum were clearly discriminated from those of A. fistulosum in the F₁ hybrids, and chromosome substitution process through continuous backcrossing was visualized. Interestingly, the chromosome region from A. galanthum, specific to male fertile plants, was detected in one chromosome of BC₄ to BC₇ generations. Based on the karyotype analysis of the male fertile plants, the chromosome was identified as the 5F chromosome. Our results confirm that the Rf locus is located on the 5F chromosome of the male fertile plants. This is the first report that identified the chromosomal location of the pollen fertility-restoring gene in A. fistulosum.