SOMATIC HYBRIDIZATION IN CITRUS USING EMBRYOGENIC CYBRID CALLUS

Embryogenic callus of a lime-type cybrid possessing the nuclear genome of lime (Citrus aurantifolia Swing.) and the mitochondrial genome of sudachi (C, sudachi Hort. ex Shirai) was induced from a somatic embryo which had been obtained through protoplast fusion between nucellar callus of sudachi and mesophyll of lime [1]. Protoplasts derived from the cybrid callus were fused electrically with mesophyll protoplasts of lemon (C. limon Burm.). After 5 months, plants were regenerated from eight fusion-derived cell clones through embryogenesis. The plants showed two types of leaf morphology; thick and broad leaf shape, identical to lemon. Chromosome counts and nuclear and mitochondrial DNA analysis confirmed that the former plants were somatic hybrids which were allotetraploid (4x = 36), possessing the nuclear genomes of both parents and the mitochondrial genome of sudachi. The latter lemon-type plants were novel cybrids possessing 18 chromosomes with the nuclear genome of lemon and the mitochondrial genome of sudachi. Lime-type cybrid plants, identical with one of the parents, were not found in this study. These results indicate that embryo-genic cybrid callus lines can be used as fusion material, resulting in further production of somatic hybrid and cybrid plants.