2019 ASHS Annual Conference

Stevia rebaudiana is the source of steviol glycosides, which act as natural non-caloric sweeteners. It would be economically advantageous to increase the productivity of steviol glycosides. Previous research has described tetraploids with shorter internode lengths and enhanced leaf size, leaf thickness, leaf productivity, and concentrations of the rebaudioside A. Rebaudioside A is a commercially important steviol glycoside. A common method to generate tetraploids has been to treat Stevia seed with colchicine and then evaluate the seedling plants produced in comparison with the parental lines. The methodology of treating seeds leaves in doubt whether or not the improved performance is a result of the creation of tetraploids or the inadvertent result of selection among the progeny. Stevia rebaudiana is inherently an outcrossing species and the seedlings vary genetically from the parents. To examine the potential advantages of tetraploids, the apical meristems of a diploid line with high rebaudioside A productivity were treated with colchicine, inducing a tetraploid line. Following vegetative reproduction through cuttings, both the diploid line and the resulting tetraploid were evaluated for leaf size leaf productivity, and 14 steviol glycosides in a field experiment at Ontario, Oregon in 2017. Although tetraploid leaf size was larger, the tetraploid resulted in decreases in dry leaf rebaudioside A content (8.4% vs 9.4%, P=0.009), dry leaf total steviol glycoside content (11.4 vs 12.8% P =0.01), and dry leaf productivity (3.3 vs 4.0 Mg/ha, P =0.008). The entire laboratory, vegetative reproduction, and field procedures were repeated in 2018 to compare three tetraploids with their diploid lines. In 2018 the leaf size and thickness were greater in the tetraploids. The tetraploids had statistically similar but lower levels of rebaudioside A (14.4% vs 15.1%, P =0.61) and total steviol glycosides (18.6 vs 18.9% P =0.75), but again leaf productivity declined (4.3 vs 6.0 Mg/ha, P =0.0002). These results suggest that improvements in Stevia productivity or steviol glycoside content via the generation of tetraploids alone may have limited success.