Inheritance of fertility restoration of male-sterility conferred by cytotype Y and identification of instability of male fertility phenotypes in onion (Allium cepa L.)

A novel onion (Allium cepa L.) cytoplasm, cytotype Y, was found in a previous study. Cytotype Y contained unique stoichiometry of coxI and orf725, a candidate gene responsible for male-sterility induction in onions. A S1 segregating population was produced from a single plant selected from PI273626. Although male-fertility segregated in this population, the ratio significantly deviated from single-gene inheritance. However, genotypes of RF31446 marker perfectly linked to Ms locus-controlling fertility restoration completely matched with male-fertility phenotypes, indicating that male-fertility restoration of male-sterility conferred by cytotype Y might be determined by the Ms locus. One plant derived from the S1 population showed discrepancy between male-fertility phenotype and RF31446 genotype. Although the RF31446 genotype was homozygous recessive, reduced amount of pollen grains were observed in anthers. Many pollen grains of the unstable male-sterile plant were deformed. Analysis of 13 molecular markers flanking the Ms locus showed no crossover between the Ms locus and the RF31446 marker. Ten more unstable male-sterile plants were identified from open-pollinated progenies of the unstable male-sterile plant. Viable seeds were successfully produced from unstable male-sterile plants, indicating that pollen grains of the unstable male-sterile plants were partially viable. In addition, an umbel containing unstable male-fertile flowers was identified from one of maintainer lines, although both male and female organs might be sterile in these flowers.