Regeneration of citrus sinensis (+) clausena lansium intergeneric triploid and tetraploid somatic hybrids and their identification by molecular markers

Somatic hybrid plants were regenerated via electrofusion between leaf-derived protoplasts of ‘Chicken heart’ sweet wampee (Clausena lansium) and embryogenic protoplasts of ‘Newhall’ navel orange (Citrus sinensis Osbeck). Most of the complete plantlets were formed via mini-grafting. Flow cytometry showed that most of the regenerants were tetraploids as expected, but unexpectedly three plantlets were triploids. Simple sequence repeat (SSR) analysis of seven randomly selected tetraploids and the three triploids showed that they had specific fragments from both fusion parents, thereby confirming their hybridity. Analysis of cytoplasmic genomes using universal primers revealed that their chloroplast DNA (cpDNA) band pattern was identical to the mesophyll parent, while their mitochondrial genomes were of the navel orange type. According to the SSR results, the triploids obtained in this study were most likely due to chromosome elimination of ‘Chicken heart’ sweet wampee prior to plant regeneration.