Gamma radiation induced variation in growth characteristics and production of bioactive compounds during callogenesis in Stevia rebaudiana (Bert.)

Stevia rebaudiana Bertoni is an important anti-diabetic medicinal herb containing non-caloric sweet compounds. In this study, the effect of gamma irradiation on growth kinetics and accumulation of various bioactive compounds were investigated during callogenesis. Callus was developed from leaf pieces inoculated on Murashige and Skoog (MS) medium containing combination of 6-benzyladenine (BA; 1.0 mg l−1), α-naphthalene acetic acid (NAA), indole butyric acid (IBA) and gibberellic acid (GA3; 0.3 mg l−1). After 30-days, vigorous calli were transferred to fresh medium and exposed to various gamma irradiations (5.0, 10, 15 and 20 Gy). It has been observed that the increasing doses of gamma rays inhibited callus proliferation (88.61–79.16%) as compared to control (95.83%). Similarly, 10, 15 and 20 Gy doses induced friable, granular and spongy callus as compared to control (compact). Furthermore, 5.0, 10 and 20 Gy doses significantly reduced the fresh callus biomass (FCB), however, 15 Gy dose enhanced FCB (1660 mg) and dry callus biomass (DCB; 159.36 mg) than control (1520; 145.92 mg). The chromatographic data revealed that 15 Gy dose slightly enhanced stevioside content (0.251 mg/g-DCB) than control (0.232 mg/g-DW), while other doses showed a negative effect on stevioside content. Higher antioxidant activity (88.73%) was observed in 20 Gy treated callus cultures. However, higher total phenolic content (TPC; 43.90 mg/g DCB) and total flavonoids content (TFC; 6.87 mg/g DCB) were observed in 15 Gy treated callus cultures. The application of gamma irradiation did not show major variation in biomass and bioactive compounds production in callus cultures of S. rebaudiana.