Studies on the induction of hairy roots in Stevia rebaudiana Bertoni

Abstract

Hairy roots are the source of secondary metabolites that are present in many medicinal plants from several years because of their characteristic properties such as to grow indefinitely on basal medium and to have stable productivity. The present study was focused on establishment of hairy roots from the leaf explants of Stevia rebaudiana Bertoni using various strains of A. rhizogenes. Amongst various strains tested, strain R1000 and R1022 were effective in inducing hairy roots. Various factors such as bacterial density of the suspension, infection duration and different period of co-culture were optimized for hairy root induction in S. rebaudiana. Among different factors studied, bacterial density of 0.6 with an infection duration of 15 min and 48 h co-cultivation period was found to be most effective. The results indicated that maximum hairy root induction (51.3 %) was observed in case of R1022 after 15 days of infection on explants. However, only 38.7% explants induced hairy roots in R1000 strain after 25- 30 days on medium containing cefotaxime (200 mg/l). The various growth parameters such as secondary root density, root elongation and root biomass production were also studied. Maximum secondary root density (3.8 roots per cm) was observed in roots transformed with R1022 strain while roots transformed with R1000 showed lower secondary root density i.e. 2.1 roots per cm. About 7.5 fold increase in root biomass accumulation was achieved in transformed roots as compared to normal roots. Thus, present study can be expanded for the possible isolation of various secondary metabolites of Stevia rebaudiana.