The T, S, and C groups of male-sterile cytoplasms of maize have distinct mitochondrial DNAs, as revealed by restriction endonuclease fragment analyses. Examination within a group has only been attempted with the S group, and no evidence of variation has been found to date. We recently examined five members of the C group, and were able to differentiate three sub-groups, based on mitochondrial DNA differences. Mitochondrial DNA was prepared from cytoplasms C, RB, BB, E, and El Salvador. Restriction enzymes Xho I, Hind III, Bam H1, Eco RI, and Sma I were used. Xho I, Hind III, and Sma I each delineated three groups: Group CI, C; Group CII, RB, BB, and E; and Group CIII, El Salvador. Bam H1 and Eco RI did not distinguish C, RB, BB, or E from each other, but did differentiate El Salvador. The pattern changes were slight between Groups CI and CII, often revealing only one fragment shifts. El Salvador was clearly distinguished, suggesting a distant relationship to C, RB, BB, or E.
No differences have been observed among chloroplast DNAs of these cytoplasms to date.
It is apparent then, that cytoplasmic heterogeneity, as reflected by mitochondrial DNA variation, is present within the C male-sterile group. Since this source of male sterility is currently utilized in hybrid production, these data may identify sources of cytoplasmic diversity potentially useful in minimizing cytoplasmic uniformity.
D. R. Pring, M. F. Conde, and C. S. Levings, III*
*Department of Genetics, N. C. State Univ., Raleigh
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