Cytological origination of the first found allotriploid tree peony, Paeonia × lemoinei ‘Oukan’ (AAB), reveled by molecular karyotype comparation

Abstract

Polyploid breeding is one of the most important approaches to improve the traits of cultivated plants, but there has been no feasible method to get polyploid tree peony. In this study, we revealed a sexual triploidization approach from a diploid intersubsectional hybrid tree peony, Paeonia × lemoinei ‘High Noon’, to an allotriploid one, P. × lemoinei ‘Oukan’, by accurate karyotyping based on genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH). The ancestor genomes from P. suffruticosa and P. delavayi, which were defined as A-genome and B-genome respectively, were clearly distinguished by GISH in ‘High Noon’ and ‘Oukan’. Nonhomologous chromosomes were successfully recognized by means of 5S and 45S rDNA FISH. Karyotype comparation based on GISH and FISH indicated that the B-genome and one of the two A-genomes in ‘Oukan’ (2n=3x=15, AAB) were highly consistent to the corresponding genomes in ‘High Noon’ (2n=2x=10, AB), implying the triploid origination via 2n gametes produced by first division restitution (FDR). In addition, it was demonstrated for the first time that the dual in series sites of 5S rDNA located on the short arm of chromosome 3 in both A and B-genomes. Besides the familiar strong 45S rDNA signals observed at terminal region of short arms, single weak 45S rDNA signal was newly detected at terminal region in the short arm of certain chromosome 1 in A-genome, and at interstitial-distal region in the long arm of chromosome 5 in both genomes. These findings provide a proof and theoretical support for tree peony polyploid breeding, and an accurate karyotyping method for genetic research of plants in Paeonia.