Interspecific hybridization in the genus Paeonia (Paeoniaceae): Polymorphic sites in transcribed spacers of the 45S rRNA genes as indicators of natural and artificial peony hybrids

The ITS1-5.8S rDNA-ITS2 regions of 33 accessions belonging to 16 species and five natural and garden interspecific hybrids of the genus Paeonia L. were sequenced. Chromatograms of the peony hybrids demonstrated the presence of the signals, corresponding to two different nucleotides at the positions differing in the parents, indicating that in the hybrids, no rDNA isogenization usually occurred, and they preserved rDNA of both parents. Analysis of these polymorphic sites (PS) showed that P. × majkoae was interspecific hybrid between P. tenuifolia and P. caucasica. The ITS of P. hybrida differs from ITS of P. × majkoae in 19 mutations. Because of this, P. × majkoae is definitely not synonymous to P. hybrida. Comparative analysis of ITS1-5.8S rDNA-ITS2 showed that species diversity in section Paeonia was based on recombination as a result of intraspecific hybridization of three haplotype families. Specifically, haplotypes A, typical of the P. tenuifolia and P. anomala genomes, haplotypes B, typical of P. mlokosewitschii and P. obovata, and haplotypes of family C, currently represented in rDNA of diploid and tetraploid forms of some Caucasian and Mediterranean species. The ITS regions many diploid peonies contain no dimorphic sites, while P. oreogeton, P. cambessedesii, P. rhodia, and P. daurica carry from 10 to 17 PS, and supposed to be the interspecific hybrids. Most of the tetraploid peonies contain from 6 to 18 PS in the ITS regions. These are alloploids with one of the parental genomes similar to that of P. mlokosewitschii (B1), or P. obovata (B3). The second parental genome in P. banatica, P. peregrina, and P. russii is represented by the genome, close to that of P. tenuifolia (A). P. macrophylla, P. mascula, P. coriacea, P. wittmanniana, and P. tomentosa carry genome of series B and genome of series C, which slightly resembles genome A.