PRODUCTION OF SOMATIC HYBRID AND AUTOTETRAPLOID BREEDING PARENTS FOR SEEDLESS CITRUS DEVELOPMENT

Allotetraploid somatic hybrid plants of 'Nova' tangelo [a sexual hybrid of 'Clementine' mandarin (C. reticulata Blanco) x 'Orlando' tangelo (C. reticulata x C. paradisi Macf.)] + 'Succari' sweet orange (C. sinensis L. Osbeck), and 'Hamlin' sweet orange (C. sinensis L. Osbeck) + 'Dancy' tangerine (C. reticulata) were regenerated following protoplast fusion. 'Nova' and 'Hamlin' protoplasts were isolated from ovule-derived embryogenic callus and suspension cultures, respectively, and fused using a polyethylene glycol method with seedling leaf-derived protoplasts of 'Succari' and 'Dancy', respectively. Plants were regenerated via somatic embryogenesis, and somatic hybrids were identified on the basis of leaf morphology, root-tip cell chromosome number, and electrophoretic analysis of peroxidase and phosphoglucose mutase isozyme banding patterns. Diploid plants were regenerated from unfused protoplasts of 'Hamlin', 'Nova', and 'Succari'. Tetraploid plants of 'Hamlin' and 'Succari' were also recovered, apparently resulting from homokaryotic fusions. No 'Dancy' plants were recovered. The somatic hybrid and autotetraploid plants can be used for interploid hybridization with selected monoembryonic scions to generate improved seedless triploid tangor/tangelo cultivars. The lack of suitable tetraploid breeding parents has previously inhibited the development of quality seedless cultivars by this method.