POLYPOLIDY AND SWEETENER INDUCTION IN DIFFERENT STEVIA VARIETIES USING COLCHICINE

The aim of the present investigation was to improve steviol glycosides (SGs) of three stevia varieties; Sponti (SPNT), China1 (CHN) and EGY1 (EGY) by obtaining new genotypes with high ratio of rebaudioside A (rebA)/stevioside (stv) using five different doses of colchicine(0, 0.025, 0.05, 0.1 and 0.2%), during 2018 and 2019 seasons at ElSabahya Research Station, Alexandria Governorate. Plants with a significant large leaf area/plant and significantly high number of leaves/plant, as well as dry matter content from the three commercial varieties, were selected and evaluated for their steviol glycosides content by using high performance liquid chromatography (HPLC). Results of buds survival rate, showed that SPNT and EGY varieties performed better than CHN. SPNT-22, CHN-31, EGY-22, EGY-23and EGY-31 mutated clones showed a significant superiority for most desirable morphological characters (leaf area/plant, number of leaves/plant as well as dry matter content)compared to other tested genotypes. HPLC showed that the sweetener contents stv and reb A percentages were affected by polyploidy induced by colchicine. Best ratio of reb A/stv was recorded by CHN-31 (3.846) which was 4.2 times higher than CHN (0.919). CHN-31, EGY-22 and EGY-31 clones recorded the highest reb A + stv percentage (77.25, 78.33 and 76.18, respectively). For EGY-31(a new clone), rebA/stv percentage was 2.6 higher compared to its commercial variety, this, consequently, decreases the bitter taste and aftertaste and increases sweet flavor. New genotypes (CHN-31and EGY-31) were obtained and selected as the best clones due to the higher sweeteners percentages recorded, which might help in meeting diabetics needs in the future