Characterization of nuclear and cytoplasmic compositions of somatic hybrid plants between sweet orange and sour orange

In the present research, flow cytometry (FCM), simple sequence repeat (SSR) and cleaved amplified polymorphic sequence (CAPS) were employed to analyze somatic hybrid plants derived from electrofusion between embryogenic protoplasts of sweet orange (Citrus sinensis Osbeck cv. Shamouti) and leaf-derived protoplasts of sour orange (C. aurantium L.) FCM showed that all of the somatic hybrid plants had two-fold fluorescence intensity values of the diploid control, indicating that they were tetraploids. SSR and CAPS were used to characterize the compositions of nuclear and cytoplasmic genomes of the somatic hybrid plants. As for SSR four primer pairs were tried and two showed polymorphisms between the fusion parents. With both primer pairs the somatic hybrid plants encompassed DNA bands from both parents, indicating that they were heterokaryonic hybrids. Amplification with some universal primers, followed by digestion with restriction endonucleases, could distinguish the fusion parents from each other. As far as mitochondrial and chloroplast DNA compositions were concerned the somatic hybrid plants shared the same banding patterns as the embryogenic parents for all of the polymorphic primer/enzyme combinations. The results herein demonstrated that the somatic hybrid plants inherited their nuclear genome from both fusion parents, whereas the cytoplasmic genomes were possibly only contributed by the embryogenic parent. Merits of the analytical methods and nuclear and cytoplasmic inheritance of citrus tetraploid somatic hybrids, together with their application, are discussed herein.