Variable penetrance among different sources of the male-fertility-restoration allele of onion

Authors: LEE, HSIANG-I - Taiwan Agricultural Research Institute; Havey, Michael

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2020
Publication Date: 2/28/2020
Citation: Lee, H., Havey, M.J. 2020. Variable penetrance among different sources of the male fertility restoration allele of onion. HortScience. 55(4):543-546. https://doi.org/10.21273/HORTSCI14709-19.
DOI: https://doi.org/10.21273/HORTSCI14709-19

Interpretive Summary: Hybrid-onion (Allium cepa) seed is produced using cytoplasmic male sterility (CMS). For the most widely used source of onion CMS, male-sterile plants possess male-sterile (S) cytoplasm and the homozygous recessive genotype at the nuclear male-fertility-restoration locus (Ms). S-cytoplasmic plants with a dominant allele at Ms are male fertile. Because male-fertility restoration is not necessary for bulb production, it may be desirable to purge dominant alleles at Ms from populations and breeding lines to facilitate the development of male-sterile inbreds for hybrid production. In this research, we used molecular markers to establish the cytoplasms and genotypes at Ms in progenies from testcrosses of male-sterile lines with three diverse inbred lines of onion [B2354, Ailsa Craig (AC) and Sapporo-Ki (Ski)] carrying dominant allele(s) at Ms. We scored male fertility of testcross progenies by visual examination of flowers and acetocarmine staining of pollen. Different sources of the dominant Ms allele and/or their genetic backgrounds significantly affected the degree of male-fertility restoration and proportion of stainable pollen, complicating visual selection against the dominant male-fertility-restoration allele. For AC and Ski, molecular markers were consistent with segregation of male fertility versus sterility of testcross progenies in greenhouse and field; however, for B2354 some testcross progenies in the field were scored as male sterile in spite of possessing the marker genotype associated with the dominant allele at Ms. These results will be of interest to onion breeders developing S-cytoplasmic male sterile lines for hybrid-onion development.

Technical Abstract: Hybrid-onion (Allium cepa) seed is produced using cytoplasmic male sterility (CMS). For the most widely used source of onion CMS, male-sterile plants possess male-sterile (S) cytoplasm and the homozygous recessive genotype at the nuclear male-fertility-restoration locus (Ms). S-cytoplasmic plants with a dominant allele at Ms are male fertile. Because male-fertility restoration is not necessary for bulb production, it may be desirable to purge dominant alleles at Ms from populations and breeding lines to facilitate the development of male-sterile inbreds for hybrid production. In this research, we used molecular markers to establish the cytoplasms and genotypes at Ms in progenies from testcrosses of male-sterile lines with three diverse inbred lines of onion [B2354, Ailsa Craig (AC) and Sapporo-Ki (Ski)] carrying dominant allele(s) at Ms. We scored male fertility of testcross progenies by visual examination of flowers and acetocarmine staining of pollen. Different sources of the dominant Ms allele and/or their genetic backgrounds significantly affected the degree of male-fertility restoration and proportion of stainable pollen, complicating visual selection against the dominant male-fertility-restoration allele. For AC and Ski, molecular markers were consistent with segregation of male fertility versus sterility of testcross progenies in greenhouse and field; however, for B2354 some testcross progenies in the field were scored as male sterile in spite of possessing the marker genotype associated with the dominant allele at Ms.