Utilization of intergeneric somatic hybrids as an index discriminating taxa in the genus Citrus and its related species

Embryogenic protoplasts of 'Shogun' mandarin ( Citrus reticulata Blanco) were electrically fused with mesophyll protoplasts from Citropsis gabunensis Swing. & M. Kell, and two green embryoids were regenerated after 3 months of culture. Two months after transfer to the regeneration medium, numerous plantlets were obtained from the embryoids. These plants grew vigorously, had well-developed root systems, and exhibited leaf characteristics intermediate to those of the parents. The absolute nuclear genome size of the regenerated plant SH2 ( 1.75 pg/4C) was the sum of those of the 'Shogun' mandarin ( 0.75 pg/2C) and C. gabunensis ( 0.97 pg/2C). The chromosome counts of the young leaves revealed that they were tetraploids ( 2n= 4x= 36). Random amplified polymorphic DNA ( RAPD) analysis of the two lines ( SH1 and SH2) verified their hybridity. Cytoplasmic genome analysis using universal primers reveal that their chloroplast ( cp) DNA banding pattern is identical to that of C. gabunensis, while the banding pattern of the mitochondrial ( mt) DNA is identical to that of the 'Shogun' mandarin. These somatic hybrids are important materials for investigating the phylogenetic relationships between these two genera in the subfamily Aurantioideae.