Phylogenetic analysis of Indian Dioscorea and comparison of secondary metabolite content with sampling across the tree

Abstract

Dioscorea (Dioscoreaceae) is a large monocot genus of species with either underground tubers or rhizomes. Many species of Dioscorea are used for food or medicine. Dioscorea is as an emerging model organism that is important in understanding plant biology and evolution. Dioscorea is rich in secondary metabolite content (e.g., diosgenin). The first objective of this study was phylogenetic analysis of Indian Dioscorea. Sampling included 16 Indian species representing approximately 50% of total Indian species. In molecular phylogenetic analyses, using plastid markers (matK, rbcL, atpB-rbcL and ndhF), the tuberous and rhizomatous species formed separate clades with strong support and members of each section formed distinct clade supporting the traditional morphology based sectional classification of Dioscorea. Results of phylogenetic analyses of Indian Dioscorea formed the basis for sampling of species for the second objective of this study, which was to compare the secondary metabolite (phenolics and flavonoid) content in representatives from different sections of Indian Dioscorea. The phenolic content and associated antioxidant activity were studied using methanolic extracts of underground parts. Six species from different sections were used in this study, which are Dioscorea alata L. (six cultivars; Enantiophyllum), D. pentaphylla L. (sect. Botryosicyos), D. esculenta (Lour.) Burkill (sect. Combilium), D. bulbifera L. (sect. Opsophyton), D. deltoidea Wall. ex Griseb. and D. prazeri Prain et Burkill (sect. Stenophora). The rhizomatous species D. prazeri and D. deltoidea showed higher phenolic and flavonoid contents than the tuberous species. Significant differences were also observed in the phenolic content and antioxidant activities among different cultivars of D. alata.