Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 1999
Publication Date: N/A
Interpretive Summary: Cytoplasmic male-sterility (CMS) is used to produce hybrid-onion seed. The CMS inbred line is the female parent of the commercial hybrid. The vast majority of hybrid-onion seed is produced using a single source of CMS called S cytoplasm. This cytoplasm traces back to a single plant identified in Davis, CA, in 1925. Its widespread use to produce hybrid onion seed represents a state of undesirable genetic uniformity. Other sources of CMS have been reported in Japan, India, and Europe. However the relationships among these uncharacterized sources of CMS and S cytoplasm are unknown. The diversity in the DNA among these male-sterility sources were studied. Sources of CMS from India were similar to S cytoplasm. Japanese and European CMS sources were also similar. One unique source of CMS was identified from India, may be unique, and is under further investigation. This new source of CMS may help diversify male-sterile cytoplasms used to produce hybrid-onion seed. Cytoplasmic diversity reduces the genetic vulnerability of onion, providing more stable production for producers of bulbs and seed and stable onion availability, at stable costs, for consumers.
Technical Abstract: Hybrid-onion (Allium cepa) seed is produced using systems of cytoplasmic-genic male sterility (CMS). Two different sources of CMS (S and T cytoplasms) have been genetically characterized. Testcrosses of N-cytoplasmic maintainers to S and T cytoplasmic lines demonstrated that different alleles or loci restore male fertility for these two male-sterile ecytoplasms. Other sources of CMS have been used or reported in Europe, Japan, and India and their relationships to S and T cytoplasms are not clear. Restriction fragment length polymorphisms were identified in the organellar genomes among commercially used male-sterile cytoplasms from Holland, Japan, and India and were compared to S and T cytoplasms. Mitochondrial DNA diversity among 58 non-S-cytoplasmic open-pollinated onion populations was also assessed. Four of five putative CMS lines selected from the Indian population Nasik White Globe were identical to S cytoplasm for all polymorphisms in the chloroplast genome and always possessed mitochondrial fragments in common with S cytoplasm. One putative CMS line from Nasik White Globe (OMI3) may be a unique source of CMS; it differed from S cytoplasm for one chloroplast polymorphism and for at least one mitochondrial probe-enzyme combination. T cytoplasm, the male-sterile cytoplasm used to produce the Dutch hybrid Hygro F1, and two sources of CMS from Japan were similar and showed numbers of mitochondrial polymorphisms similar to that observed among the 58 non-S-cytoplasmic open-pollinated populations. This research demonstrates that similar male-sterile cytoplasms have been independently isolated and exploited for hybrid-seed production in onion, with the possible exception of one putative CMS line from Nasik White Globe.