Submitted to: Journal of American Society of Horticulture Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 1999
Publication Date: N/A
Interpretive Summary: The production of hybrid-onion seed requires a system of male sterility. The primary source of male sterility used world-wide is S cytoplasm, which traces back to a single male-sterile plant identified in Davis, CA, in 1925. This cytoplasmic uniformity is analogous to the situation that led to an epidemic of the Southern Corn Leaf Blight of maize in the early 1970s. In an attempt to diversify male-sterile cytoplasms used to produce hybrid-onion seed, the cytoplasm of the wild species Allium galanthum was introduced into elite populations of the bulb onion. This alien cytoplasm conditions complete male sterility. In addition, male sterility is easier to score than for S cytoplasm. The seed yield of the galanthum-cytoplasmic populations were not significantly different from that of elite onion lines. It is intended that these galanthum-cytoplasmic onion populations be used as an alternative male-sterile cytoplasm for the commercial production of hybrid-onion seed.
Technical Abstract: The primary source (S cytoplasm) of cytoplasmic-genic male sterility (CMS) used to produce hybrid-onion (Allium cepa) seed traces back to a single plant identified in 1925 in Davis, CA. Many open-pollinated populations also possess this cytoplasm, creating an undesirable state of cytoplasmic uniformity. Transfer of cytoplasms from related species into cultivated populations may produce new sources of CMS. In an attempt to diversify the cytoplasms conditioning male sterility, the cytoplasm of Allium galanthum was backcrossed for seven generations to bulb-onion populations. The flowers of galanthum-cytoplasmic populations possess filaments with no anthers and upwardly curved perianth, making identification of male-sterile plants easier than for either S- or T-cytoplasmic male-sterile onion plants. Mean seed yield per bulb of the galanthum-cytoplasmic populations was measured in cages using flies as pollinators and was not significantly different from one of two S-cytoplasmic male-sterile F1 lines, a T-cytoplasmic male-sterile inbred line, or N-cytoplasmic male-fertile lines. Male sterile lines possessing either the S or galanthum cytoplasm were each crossed with populations known to be homozygous dominant and recessive at the nuclear locus conditioning male-fertility restoration of S cytoplasm and progenies scored for male-fertility restoration. Nuclear restorers of S cytoplasm did not condition male fertility for the galanthum-cytoplasmic populations. It is intended that these galanthum-cytoplasmic onion populations be used as an alternative male-sterile cytoplasm for the commercial production of hybrid-onion seed.