Polygonatum is a genus belonging to the Liliaceae family. It is distributed throughout the Northern Hemisphere and 16 of the species grow naturally in the wild in South Korea. In oriental medicine, the rhizomes of Polygonatum are processed by drying, grinding, steaming, or calcining. The Polygonatum rhizomes are classified into two different medicinal groups of Okjuk (Polygonati Odorati Rhizoma) and Hwangjeong (Polygonati Rhizoma). However, it is difficult to distinguish the two groups of medicinal herbs by their morphological and chemical differences, thus making it easy to confuse one for the other. Therefore, a clear classification standard needs to be established so as to be able to discriminate between them. In this study, the morphological characteristics of the Polygonatum plants were examined. The matK, rpoC1, rpoB2, and psbA-trnH coding regions in the chloroplast DNA (cpDNA) of 12 leaf accessions belonging to 7 of the Polygonatum spp. and 61 Polygonatum sequence data sourced from NCBI Genbank the samples were sequenced. The differences in SNPs among the DNA sequences were analyzed.
Comparisons of the leaf characteristics, such as length and width ratio, shape, margin, venation, leaf arrangement, and apex between the samples were made. A few of the P. falcatum, P. stenophyllum, and P. sibiricum samples were distinguishable from the other Polygonatum species based on their morphological characteristics. However, it was difficult to discriminate the rest of the processed rhizomes, thus, cpDNA sequence analysis was performed.
The average GC content of the rpoC1 region was the highest while it was the lowest at the matK region out of 4 primers. From the mean interspecific and intraspecific genetic distances results, matK showed the largest barcoding gap with 15 times higher interspecific vs. intraspecific distance. The average intraspecific distance of matK and psbA-trnH was similar to each other (approximately 0.001%). The intraspecific variation rate of rpoC1 and rpoB2 was confirmed to be low with an average intraspecific distance at 0%. Based on the phylogenetic analysis, matK, rpoC1, rpoB2, and psbA-trnH were useful in distinguishing P. stenophyllum and P. sibiricum respectively.
In conclusion, the four coding regions, matK, rpoC1, rpoB2, and psbA-trnH were useful in discriminating between P. stenophyllum and P. sibiricum. Furthermore, it was possible to discriminate the individual germplasm within the species by using the combination of the results obtained from rpoB2, rpoC1, and matK.
DNA barcoding analysis was useful in the authentication of Polygonatum species, especially, when the limitation of using a single primer is supplemented by combining two or more primer sequences. In addition, the results of this research will be used for standardization of medicinal herbs resources as well as the development of molecular markers for the authentication of Polygonatum medicinal materials.