**Abstract**

Artemisinin is an anti-malarial sesquiterpene lactone isolated from *Artemisia annua* L., a traditional Chinese herb of the family Asteraceae. The plant contains relatively low artemisinin content, ranging from 0.01 to 0.8% of the plant dry weight, depending on the geographical origin, seasonal, and somatic variations. Ionizing radiation has been recognized as a powerful technique for plant improvement, especially in crop plants. This technique creates genetic variability in plants, which can be screened for desirable characteristics. Very little is known about the effect of gamma irradiation on the potential increase of artemisinin production in *A. annua*. In this study, 130 shoot tips excised from the population of in vitro *A. annua* plantlets (with an average leaf artemisinin content of 0.18 ± 0.09%) were exposed to 5 Gy 60Co gamma irradiation and subsequently transferred to a suitable medium for in vitro development of plantlets. The resulting 90 stable survived after four passages appeared to have a wide variation of artemisinin content, ranging from 0.02 to 0.68% of dry weight. All the viable plantlets were then transferred from the in vitro cultures to ex vitro conditions both in a greenhouse and an open field. A significant correlation was observed between artemisinin content among individual pairs of the vitro plantlets and ex vitro mature plants, with the correlation coefficient (R<sup>2</sup> ) values of 0.915 for the greenhouse plants and 0.797 for the open field plants. Among these, the highest artemisinin-containing plant appeared to accumulate 0.84% artemisinin of dry weight in the open field, which is almost five times higher than the original plants. These results suggest that gamma irradiation with 5-Gy dose can produce viable variants of *A. annua* that can maintain the biosynthetic capability of artemisinin throughout the in vitro-ex vitro transfer and development of the first generation of mature plants.

**Keywords:** artemisinin, *Artemisia annua* L., gamma irradiation, in vitro plantlets, ex vitro plants
