Linkage equilibrium among tightly linked RFLPs and the Ms locus in open-pollinated onion populations

Abstract

Cytoplasmic male sterility (CMS) in onion (Allium cepa L.) is conditioned by the interaction of the male-sterile (S) cytoplasm with recessive alleles at a single nuclear male-fertility restoration locus (Ms). In order to seed propagate male-sterile plants (S msms), onion breeders must identify maintainer lines possessing normal (N) male-fertile cytoplasm and homozygous recessive at the Ms locus (N msms). Molecular markers have been identified distinguishing N and S cytoplasms and closely linked to the nuclear Ms locus. In this study, we evaluated testcross progenies from randomly selected N-cytoplasmic plants from three open-pollinated populations for nuclear restoration of male fertility over at least three environments. The Ms locus and linked restriction fragment length polymorphisms (0.9 and 1.7 cM) were at linkage equilibrium in all three open-pollinated onion populations, indicating that these linked markers cannot be used to identify maintaining genotypes in open-pollinated onion populations. However, cytoplasmic evaluations were effective in reducing the number of testcrosses required to identify CMS-maintaining genotypes.