Abstract
Large-scale artificial cultivation of medicinal Glycyrrhiza plants is imperative due to the short supply and the dramatic decline in wild populations. Xinjiang is the main Glycyrrhiza production area of China, but the quality of cultivated Glycyrrhiza plants is low due to the mixed cultivation of multiple seeds of unknown origins. To explore the identification method and efficient cultivation of elite Glycyrrhiza germplasms in Xinjiang, China, in this study, the differences in leaf micromorphological characteristics and main active ingredients of 6 Glycyrrhiza species and 2 hybrids in Xinjiang were clarified, and then identification on the basis of DNA barcode was conducted. The results showed that: (1) The combination of nuclear gene ITS2, chloroplast nucleic acid sequences trnH-psbA and trnV-ndhC could accurately identify Glycyrrhiza species and hybrids, and the calculation of genetic distance could preliminarily determine the maternal species of hybrids. (2) The upper and lower epidermal cells of the Glycyrrhiza plant leaves were nearly polygonal, and the anticlinal walls were deep or shallowly corrugated. The upper and lower epidermis had stomata, and rectangular or oblong-oval stomata could be classified according to the length-to-width ratio. The quantitative traits such as glandular trichomes’ diameter and density were significantly different between species. The ornamentation of epidermal wax had three types: smooth, coarse-grained, and dense and fine-striped. (3) Cluster analysis of 11 micromorphological traits such as glandular trichomes diameter (GTDi) with absolute weight above 0.7 from the first four components showed that the 6 Glycyrrhiza species and 2 hybrids were clustered into one category, and the hybrids had a close genetic relationship with G. uralensis and G. inflata, which was consistent with the DNA barcode identification results. (4) The comprehensive evaluation of germplasms in Xinjiang found that Glycyrrhiza glabra was superior to other germplasms (Glycyrrhiza glabra > G. glabra var. Glandulosa > G. uralensis > G. inflata > G. aspera > hybrid I > G. prostrata > hybrid II), indicating that the hybridization reduced the medicinal value of Glycyrrhiza species. This study is of great significance for the identification of Glycyrrhiza species, the conservation of elite Glycyrrhiza germplasms, and the healthy development of the medicinal plant market.