6 NEW SOMATIC CITRUS HYBRIDS AND THEIR POTENTIAL FOR CULTIVAR IMPROVEMENT

Protoplast culture following polyethylene glycol (PEG)-induced fusion resulted in the regeneration of somatic hybrid plants from the following six parental combinations: Citrus sinensis (L.) Osbeck cv. Hamlin + Severinia buxifolia (Poir.) Tenore (Chinese box-orange); C. reticulata Blanco cv. Cleopatra + Poncirus trifoliata (L.) Raf. cv. Flying Dragon; C. reticulata cv. Cleopatra + Swingle citrumelo (C. paradisi Macf. x P. trifoliata); C. sinensis cv. Hamlin + C. jambhiri cv. Rough lemon; C. sinensis cv. Valencia + C. jambhiri cv. Rough lemon; and C. paradisi cv. Thompson + 'Murcott' tangor (purported hybrid of C. reticulata x C. sinensis). Diploid plants were regenerated from nonfused embryogenic culture-derived protoplasts of 'Cleopatra' mandarin and 'Hamlin' and 'Valencia' sweet orange, and from nonfused leaf-derived protoplasts of Rough lemon and 'Murcott'. Regenerated plants were classified according to leaf morphology, chromosome number, and isozyme analyses. All of the somatic hybrids reported herein are tetraploid (2n = 4x = 36), with the exception of the 'Hamlin' + S. buxifolia hybrid, which was unexpectedly found to have a chromosome number of 2n = 27. These six new somatic hybrids have potential in citrus scion and rootstock improvement for commercial use.