Karyotypic and molecular cytogenetic characterization of diploid and polyploid accessions of medicinal herbs in the genus Paris from northern Thailand

Paris is a genus of medicinal plants in the family Melanthiaceae. For the use in traditional medicine and for trading in local markets, rhizomes of Paris plants are collected from their native habitats. Due to its slow growth and excessive harvesting, the species is currently facing the risk of extinction. The aim of the present study was to cytogenetically characterize Paris plants from the mountainous regions of northern Thailand in order to obtain characteristics that may be species-specific for use in taxonomical and diversity studies. Chromosomes were isolated from rhizome-grown root tips from the total of 20 Paris accessions. Of these, 12 were diploid (2n = 2x = 10), 2 were triploid (2n = 3x = 15), one was tetraploid (2n = 4x = 20) and 5 were mixoploid accessions. The diploid accessions from Chiang Rai and Nan provinces had the most common basic karyotype 6m+4t whereas those from Chiang Mai province showed 6m+4st and 4m+2sm+4st, indicating differentiation at the species level. The analysis of karyotypes and ribosomal gene mapping by FISH (fluorescence in situ hybridization) indicated autotriploidy arising spontaneously within a diploid population and autotetraploidy via endoreduplication in the mitotic cell division. The ribosomal FISH also revealed a novel map of 5S and 45S rDNA, including the ancestral 5S-45S linked sites. The findings of our research support the ongoing species diversification among Thai Paris taxa.