Breeding of triploid citrus cultivars .1. Production of triploids from satsuma mandarin (Citrus unshiu Marc) x tetraploid ponkan mandarin (Citrus reticulata Blanco) crosses

Crosses between satsuma mandarins and tetraploid ponkan were made to produce triploid hybrid cultivars. Triploid embryos were obtained from the crosses using three seed parents, 'Ootsu No. 4','Aoshima' and 'Imamura', which produced comparatively small numbers of embryo per seed. Of the three, the frequency of triploid embryo production per fruit was highest in 'Aoshima'. The frequency of triploid embryo production per seed in undeveloped seeds was higher than that in fully developed seeds. By the embryo rescue technique, triploid plants were obtained efficiently from the embryos of undeveloped seeds. Tetraploid plants were also obtained from fully developed seed of 'Ootsu No. 4' and 'Aoshima'. RAPD analysis showed that all the triploid plants were hybrids and the tetraploid plants were also hybrids or natural auto-tetraploids. Two hybrid embryos in one seed with identical banding RAPD patterns on agarose gels, indicate that the embryos are derived from the same single egg cell.