Inheritance of fertility restoration of male-sterility conferred by cytotype Y and identification of instability of male fertility phenotypes in onion (<i>Allium cepa</i> L.)
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A novel onion (<i>Allium cepa</i> L.) cytoplasm, cytotype Y, was found in a previous study. Cytotype Y contained unique stoichiometry of <i>coxI</i> and <i>orf725</i>, a candidate gene responsible for male-sterility induction in onions. A S<sub>1</sub> 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 <i>Ms</i> 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 <i>Ms</i> locus. One plant derived from the S<sub>1</sub> 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 <i>Ms</i> locus showed no crossover between the <i>Ms</i> 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.
