Abstract: Wide somatic hybridization was conducted between diploids of embryogenic protoplasts isolated from elite "Bonanza" navel orange ( Citrus sinertsis (L.) Osbeck) and leaf protoplasts from edible "Chicken Heart" Chinese wampee ( Clausena lansiurn (Lour.) Skeels). Fusion products regenerated into shoots after 8 months of culture. Most shoots unexpectedly rooted well. The hybrid shoots were initially unifoliate, then bifoliate and/or trifoliate leaves appeared probably inheriting from the compound leaf character of Cl. lansium. More than ten randomly selected shoot- and root-tips were not 2n = 4x = 36 as expected, but 2n = 6x = 54 as identified by chromosome counting, suggesting that chromosome doubling occurred rather than chromosome elimination in this remote fusion combination. The hybridity of embryoids, unrooted and rooted shoots was revealed by RAPD analysis. This is the first report on hexaploid somatic hybrid plants regenerated from fusion between diploids in Aurantioideae. The possible reason for the unexpected ploidy variation was also discussed.

Key words: Citrus, Clausena, Electrofusion, Somatic hybridization, Ploidy variation, Randomly amplified polymorphic DNA