INTERGENERIC SOMATIC HYBRIDS BETWEEN CITRUS AND ATALANTIA OR SEVERINIA BY ELECTROFUSION, AND RECOMBINATION OF MITOCHONDRIAL GENOMES

Two intergeneric hybridizations through protoplast fusion between the embryogenic callus cells of 'Seminole' tangelo (Citrus reticulata Blanco X C. paradisi Macf.) and leaf cells of Indian atalantia (Atalantia monophylla DC.) or Chinese box-orange (Severinia buxifolia (Poir.) Tenore) were performed to overcome the genetic incompatibility. We were successful in regenerating whole plants of 16 somatic hybrids between 'Seminole' tangelo and Indian atalantia, and 46 somatic hybrids between 'Seminole' tangelo and Chinese box-orange, and hybridity was confirmed by Southern blot hybridization with rDNA. The mitochondrial DNA (mtDNA) of the somatic hybrids between 'Seminole' tangelo and Indian atalantia was identical to that of 'Seminole' tangelo, when rrn 26 and cox I were used as probes. However, when atpA was used as a probe, a 'Seminole' tangelo-specific fragment was found missing besides an Indian atalantia-specific fragment. The band pattern obtained by chloroplast DNA (cpDNA) analysis was identical to that of Indian atalantia. On the contrary, somatic hybrids between 'Seminole' tangelo and Chinese box-orange showed the mtDNA band pattern identical to that of 'Seminole' tangelo, when atpA and cox I were used as probes. However, analysis by rm 26 probe showed the presence of a part of a Chinese box-orange-specific band in addition to a 'Seminole' tangelo-specific band. The cpDNA of the somatic hybrids was identical to that of Chinese box-orange. These results suggest the occurrence of mitochondrial recombination between parents.