Abstract: The formation and maintenance of the cytotype mixture in plant natural populations has been found related to genetic and epigenetic variations of genomes. We investigated the patterns of genetic variation, genetic structure and methylation levels, as well as epigenetic differentiation, of a cytotype mixture population of the Actinidia chinensis complex by amplified fragment-length polymorphism (AFLP) and methylation-sensitive amplification polymorphism (MSAP). The mixture population had high genetic and epigenetic diversity. The relationship between population genetic diversity and altitude but not epigenetic diversity and altitude was significant (P<0.05). As well, patterns of genetic and epigenetic variation were not positively correlated. Analysis of molecular variance revealed that most genetic and epigenetic variations occurred within ploidy races (97.65% vs 99.84%, P<0.05). Neighbor-joining tree analysis based on AFLP analysis revealed that the same ploidy individuals clustered preferentially, with no obvious cluster based on ploidy levels in the MSAP tree. The total methylation level in the cytotype mixture population was 24.86%. Moreover, tetraploids and hexaploids showed more variation than diploids in genomic methylation, including increase and loss of methylation loci. We provide a theoretical basis to understand the formation and maintenance mechanism in the cytotype mixture population of A. chinensis.

Key words: Actinidia chinensis, cytotype mixture, DNA methylation, genetic structure, polyploidy