| Stevia rebaudiana (stevia) is gaining agricultural importance due to its natural production of non-caloric steviol glycosides, which can be extracted and incorporated into natural, zero-calorie sweeteners. Of the several steviol glycosides produced by stevia, those produced in the largest concentrations, such as rebaudioside A, are often criticized by consumers as having a bitter aftertaste. Other glycosides, such as rebaudioside D, are reported to have a superior flavor profile, but are produced in much smaller concentrations. The environmental and genetic control of steviol glycoside synthesis is poorly understood. The objectives of this research were: 1) to determine how daily light integral (DLI) influences glycoside concentrations and relative proportions, particularly for rebaudioside D and 2) to elucidate the genetic control of rebaudioside D synthesis from rebaudioside A. DLI influenced both glycoside concentration and relative proportion in a glycoside-specific manner. Using traditional breeding, populations were created via controlled crosses where parents varied in the percentage of rebaudioside D calculated from the total of rebaudiosides A and D. The production of rebaudioside D appears to be regulated by a single dominant gene controlling the presence/absence of the precursor compound, rebaudioside A. Some of the individual populations in this study exhibited correlations unique to each population regarding traits of interest, demonstrating the variability in stevia. Future breeding efforts could harness this variability in addition to knowledge of precursor glycoside content as a resource to improve future stevia lines. |
