EMBRYOGENESIS INVITRO AND NONCHIMERIC TETRAPLOID PLANT-RECOVERY FROM UNDEVELOPED CITRUS OVULES TREATED WITH COLCHICINE

A method was developed to produce nonchimeric, autotetraploid Citrus plants via in vitro somatic embryogenesis in the presence of colchicine. Undeveloped ovules from immature fruit of 'Valencia' sweet orange (Citrus sinensis [L.] Osb.) and 'Orlando' and 'Minneola' tangelos (Citrus reticulata Blanco x Citrus x paradisi Macf.) were held on Murashige and Tucker medium with 500 mg malt extract/liter and 0.00%, 0.01%, or 0.10% colchicine for 21 days. Embryogenesis from tangelo ovules was suppressed by 0.10% colchicine, but no such effect was observed among sweet orange ovules. Colchicine treatments had no subsequent effect on embryo germination. The numbers of chromosomes in root tip cells showed that both tetraploid and diploid 'Valencia' and 'Orlando' plants were recovered from colchicine treatments. 'Minneola' cultures produced only diploid plants. Tetraploid plant morphology was typical for Citrus tetraploids. Examination of chromosome numbers in root tip, shoot, and leaf meristems indicated that the regenerants were nonchimeric. Such nonchimeric tetraploids will be useful parents for interploid hybridization directed toward development of seedless triploid Citrus scion cultivars.