Mitochondrial DNA variation in maintainer lines (O-type) of sugarbeet.

The mitochondrial genome influences the cytoplasmic male sterile trait in sugarbeet (Beta vulgaris L.); therefore, comparisons of mitochondrial DNA structure and organization of sterile and normal cytoplasm can elucidate the molecular basis of male sterility. Mitochondrial DNA variability in maintainer lines of sugarbeet was characterized by restriction fragment length polymorphisms (RFLP). Mitochondrial DNA of four lines from a North American monogerm population and six lines from a Russian monogerm population were restricted with EcoRI and hybridized with coxII and atpA probes. EcoRI digestion revealed three distinct restriction patterns: one typical of the pattern for normal cytoplasm of sugarbeet and two that resembled patterns for mtDNA from fertile plants of wild beet, B.v. ssp. maritima. The probing of mtDNA with coxII revealed two mitochondrial variants differing in a 1.8 kbp hybridization signal. The atpA probe identified alterations of mitochondrial DNA which resulted either in the appearance of a new 3.5 kbp band or in the absence of a 4.4 kbp band and the presence of 3.5 kbp signal. Changes in mitochondrial genome organization were observed only in maintainer lines from the Russian population. These differences in mitochondrial DNA provide evidence for the existence of two unique fertile cytoplasms for use in the development of male-fertile sugarbeet breeding lines. RFLP analysis and molecular characterization of mitochondrial DNA of male-fertile germplasm provides breeders useful information on genetic diversity within O-type lines. Maintainer lines with unique mtDNA can be used to diversify sugarbeet germplasm.