Cytoplasmic male sterility and nuclear restorer genes in a natural population of Beta maritima: genetical and molecular aspects.

One natural population (F0 generation) of Beta maritima situated on the French Atlantic coast has been analysed. It was composed of 62% female, 30% hermaphrodite and 8% intermediate plants. The analysis of half-sib progeny (F1 generation) obtained from in situ open pollination demonstrates the cytoplasmic determination of male sterility in Beta maritima and the restoration of fertility by nuclear genes. The mitochondrial DNA (mtDNA) and the chloroplast DNA (ctDNA) of sixteen F1 plants, extracted from offspring of the three sexual phenotypes, were analysed using the restriction enzymes Sal I and Bam HI, respectively. Two cytoplasmic lines with their own peculiar genetic characteristics were distinguished using the restriction enzyme patterns of mtDNA: (i) the S cytoplasmic line was found in segregating progeny of two F0 plants; all three phenotypes were produced (that is, progeny including hermaphrodite, female and intermediate plants); (ii) the N cytoplasmic line was found in the progeny of one F0 hermaphrodite plant; this produced only hermaphrodites. Thus, segregating and non-segregating hermaphrodite F0 plants can be distinguished. The nuclear genes maintaining sterility or restoring fertility are expressed in line S. At the same time the analysis of Beta vulgaris material has been carried out at the molecular level: N cytoplasmic lines of B. vulgaris and B. maritima differed only by 3 fragments of mtDNA; but the S cytoplasmic line of B. maritima was very different from Owen's cytoplasmic male sterile line of B. vulgaris. No variation in the ctDNA pattern was detected within and between the two taxa.