North Carolina State University and USDA/ARS

A Brazilian source of cms-S

--Michel Ragot, Paul H. Sisco, Major M. Goodman and Charles W. Stuber

Cms-S has been discovered in Cristal MG III, a racial composite of seven Brazilian maize accessions collected by Dr. M. M. Goodman, MM. This is the first report of cms-S in a South American race of maize. The seven accessions composing Cristal MG III are BR2307, BR2321, BR2659, BR2660, BR2674, BR2681, and BR2696. Cristal is a hard flint, sometimes white and sometimes yellow seeded. Male sterility was first noted among plants in an F2 population of a Cristal-derived inbred crossed by Mo17. To confirm cytotype, mitochondrial DNA from the Cristal-derived inbred and the original Cristal MG III composite was isolated, digested with BamHI, and electrophoresed on agarose gels. BamHI digestion patterns, as visualized by ethidium bromide staining, were compared with those of known cytoplasms. Both digested and undigested Cristal mtDNA showed two intense bands that co-migrated with the S1 and S2 plasmids of cms-S. Further classification into different cms-S subgroups can be done on the basis of restriction digest patterns of mtDNA (Sisco, PH et al., TAG 71:5-19, 1986) or on the basis of presence/absence of a 1.94kb plasmid found in certain cms-S accessions (Carlson and Kemble, Plant Molec. Biol. 4:117-123, 1985). The mtDNA pattern of Cristal appeared to match the BamHI pattern of the "CA subgroup" of cms-S, but the 1.94kb plasmid was also present as shown by hybridization of the plasmid to a Southern blot of the mtDNA. The mtDNA of Cristal MG III is thus most similar to that of the "J" accession of cms-S (Beckett, JB, Crop Sci. 11:724-727, 1971).

The finding of cms-S cytoplasm in a South American race of maize is of interest both for the origin of S cytoplasm and of the Cristal race. Previous discoveries of cms-S have pointed to an origin in Mesoamerica (Weissinger et al., Genetics 104:365-379,1983; Doebley and Sisco, PH, MNL 63:108, 1989). Nevertheless, Levings et al. (NATO Adv. Inst. Series 31:363-372, 1983) presented evidence that the S1 molecule of cms-S could have arisen from a recombination between the R1 and R2 plasmids found in certain other South American races of maize, such as Racimo de Uva. Thus two possible explanations for cms-S in Cristal MG III are 1) cms-S was created de novo from a recombination between the R1 and R2 plasmids in South America, or 2) cms-S cytoplasm was imported to Brazil from Mesoamerica.

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