A FERTILE REVERTANT FROM PETALOID CYTOPLASMIC MALE-STERILE CARROT HASA REARRANGED MITOCHONDRIAL GENOME

A spontaneously derived fertile plant was recovered from a petaloid cy toplasmic male-sterile (CMS) carrot inbred line. Genetic analysis indi cated a single nuclear gene was responsible for the restoration to fer tility. Within a family segregating for the nuclear restorer in combin ation with the sterility-inducing cytoplasm, fertile plants were recov ered that could not restore fertility when crossed to sterile genotype s. Genetic analysis indicated cytoplasmic reversion for fertility, and Southern analysis, comparing mtDNA organization of the fertile revert ant and its CMS progenitor, identified mitochondrial genome rearrangem ents. Hybridization of cosmids representing a 108-kb subgenomic circle of the sterile line to DNA of a fertile maintainer and fertile revert ant lines indicated a similar mtDNA organization for these genotypes t hat was distinct from that of the sterile line. Six restriction fragme nts totalling 43.2 kb were common to the fertile maintainer and revert ant and absent in the sterile; other restriction fragments totalling 3 8.2 kb were present only for the sterile line. Unique fragments of low stoichiometry, two for the fertile maintainer and three for the rever tant, distinguished these lines. The reversion to fertility in the ste rile line could have resulted from the amplification of a mitochondria l submolar genome highly homologous to that found in the fertile maint ainer line.