Effect of acute gamma irradiation towards morphological characteristics, genetic variations and stevioside compound of Stevia rebaudiana / Aida Khalida Hamdan

Stevia rebaudiana is a short-day plant that would generate flower early under a constant day length less than 12 hours in Malaysia. The main problem of stevia in Malaysia is its photoperiod sensitive trait that could stop producing more leaf biomass and resulting in low content of steviol glycosides compound. Cultivation of stevia in Malaysia is a challenge due to the lack of suitable variety that suit the local condition. Therefore, development of new stevia variety is needed. The method applied was acute gamma irradiation with six doses (50 Gy, 100 Gy, 250 Gy, 325 Gy, 400 Gy and 500 Gy) to investigate the effect of radiation on stevia seeds. The qualitative and quantitative analysis were carried out to determine the changes of morphological traits of irradiated stevia. The LD50 value was at 182 Gy indicated that 50% of irradiated stevia seedlings would die if exposed to more than 182 Gy. The number of days for seed to germinate varied in all treatments and none of the seedlings survived at 400 Gy and 500 Gy of irradiation. The plant height recorded was highest in treatment 50 Gy (142.0cm±1.98). Meanwhile, for other parameters such as the number of leaves, the number of branches were decreased as the dose increases. The parameter mentioned on 250 Gy and 325 Gy obtained decreased in numbers as the doses were exceed the LD50. The findings of this study suggest that doses of radiation range below than 325 Gy were recommended for the improvement of stevia by acute gamma irradiation. Next, study on genetic variation and steviol glycosides content were carried out to evaluate the effect of gamma irradiation on the stevia plant. The study on molecular analysis was performed using PCR based ISSR marker to assess the genetic variation of the irradiated stevia by using
ten ISSR primers. Based on the observation, ISSR molecular analysis generated 81.48% of genetic polymorphism and showed 18.52% on monomorphism.