Comprehensive Identification of Rhubarb Species Based on DNA Barcoding and Multiple-Indicator Quantification

Rhubarb is a significant medicinal herb in China. Its adulteration or fabrication is common in the market. Consequently, it is necessary to establish a comprehensive identification method to accurately identify genuine rhubarb and its adulterants. In this study, the sequences of chloroplast genes rps3-rpl22 and rpl16 from three genuine rhubarbs (Rheum tanguticum, Rh. palmatum and Rh. officinale) and their adulterants (Rumex japonicus and Rumex spp.) were amplified, sequenced and subjected to genetic analyses. The genetic distances for rps3-rpl22 and rpl16 between genuine rhubarbs and their adulterants showed that there was an evident barcoding gap, which allowed the adulterants to be distinguished from the genuine rhubarbs, as demonstrated by a neighbor joining tree. Additionally, Rh. officinale could be distinguished from the other two genuine rhubarbs. The anthraquinone, sennoside, polysaccharide and protein contents were analyzed in seven rhubarbs using high-performance liquid chromatography and ultraviolet spectrophotometry. Cluster and principal component analyses results showed that Rh. tanguticum and Rh. palmatum could be effectively distinguished. The study suggests that DNA barcoding based on rps3-rpl22 and rpl16 sequences coupled with multiple-indicator quantification can be successfully applied to identify rhubarb species and distinguish among the three genuine rhubarbs, and this can provide a scientific foundation for rhubarb quality assurance.