Molecular characterization of the nuclear and cytoplasmic genomes of intergeneric diploid plants from cell fusion between Microcitrus papuana and Rough lemon

Simple-sequence-repeat (SSR) and PCR-RFLP were employed to characterize the nuclear and cytoplasmic genomes of intergeneric diploid plants derived from symmetric fusion between Microcitrus papuana Swingle and Rough lemon (Citrus jambhiri Lush). Three out of five SSR primers distinguished the fusion parents from each other and the regenerated plants showed band profiles completely identical to the leaf parent, Rough lemon. Amplified products from the intergenic regions of cpDNA between trnD-trnT were digested with HaeIII and MspI, and those between trnH-trnK were digested with HinfI, and both the regenerated plants and Rough lemon shared the same band patterns, which were different from the embryogenic parent, M. papuana. With mtDNA, only 2 out of 12 primer pair/restriction enzyme combinations (nad4 ex 1-2/TaqI and nad4 ex 1-2/HindIII) revealed polymorphisms between the fusion parents. With the former combination the regenerated plants showed the same fragment distribution as that of the embryogenic parent, M. papuana, whereas with the latter, a novel band absent in the fusion parents was detected in all of the regenerated plants, suggesting a possible rearrangement. The present research indicates that the plants analyzed were putative cybrids containing nuclear DNA and cpDNA from Rough lemon and mtDNA from M. papuana. Presumed mechanisms leading to the regeneration of diploid hybrid plants following symmetric fusion are discussed herein.