Inter-generic mitochondrial genome recombination in somatic hybrids between Citrus and Poncirus

Abstract

SummaryThe genetic composition of somatic hybrids between ‘Page’ tangelo (Citrus reticulata × C. paradisi) and trifoliate orange (Poncirus trifoliata) were analysed in fifteen stochastically selected, fusion-derived plants. Flow cytometry revealed that all plants were tetraploids, and nuclear simple sequence repeats (SSR) showed that all plants possessed SSR loci from both fusion parents. Organellar genome compositions were examined using cleaved amplified polymorphic sequences (CAPS) and restriction fragment length polymorphism (RFLP) analyses. Mitochondrial genome (mtDNA) analyses indicated that all 15 hybrids had inherited regions of mtDNA common to both parents, and some specific bands from both fusion parents were also present in the hybrids, indicating the occurrence of mtDNA recombination in these somatic hybrids. No chloroplast genome (cpDNA) polymorphisms were detected by RFLP or CAPS analyses; however, random segregation of cpDNA was revealed by chloroplast simple sequence repeat (cpSSR) analyses. To evaluate genetic variation in mtDNA among the hybrids and both fusion parents, a dendrogram based on the RFLP data for 15 polymorphic mtDNA markers was generated by the Unweighted Pair Group Method with Arithmetic mean. The results showed that the 15 hybrids, and both parents, were located in three distinct clusters, and no variation was detected among these hybrids. The hybrids showed closer genetic similarity coefficients to the suspension cell parent than to the mesophyll cell parent, which demonstrated biased transmission of mtDNA. This is the first report of mtDNA recombination between Citrus and Poncirus by somatic fusion.