IMPROVEMENT OF STEVIA (Stevia rebaudiana BERTONI) AND STEVIOL GLYCOSIDE THROUGH TRADITIONAL BREEDING AND BIOTECHNOLOGICAL APPROACHES

Stevia rebaudiana Bertoni, widely known as sweet leaf, is a perennial herbal species of the Asteraceae family, which is widely used as a natural sweetener in many countries around the world due to the great demand for its steviol glycosides (SVgly) contents particularly rebaudioside A (Reb. A). This review article shows some important selected data accessible in previous scientific studies on crop improvement and SVgly production in stevia by traditional breeding methods and biotechnological breeding approaches. This review article reflects on improve the production of Stevia rebaudiana by using different breeding methods. S. rebaudiana plants are conventionally propagated through cuttings, but this traditional method cannot produce a large number of plants. The seeds of this species are smaller in size and the germination percentage is very low with a significant problem of low fertility and typically displays a low rate of germination. The seed yield and poor germination ability are some of the significant constraints caused by self-incompatibility. Therefore, modern techniques of propagation such as in vitro regeneration or tissue culture are needed to enhance the production for this important species. A real breeding key of stevia is developing SVgly and yield. It is attractive to develop and select a new variety with a higher content of stevioside and a higher Rebaudioside A (Reb. A). Recurrent selection is a particularly appropriate method for the enhancement of stevia quantitative traits in cross-pollinated species. Heterosis may also be a method for breeders to produce new improved varieties. The mutation method could play a significant role in the breeding improvement programs of stevia. Breeding of polyploidy could be valuable as they have larger leaves and potential for higher SVgly than the standard diploid. Modern techniques can also be explored, such as molecular markers, HPLC and mass spectrometry, to assist in quicker breeding for higher glycoside and yield traits.