Yield of Diterpene Glycosides from the Leaves of Stevia rebaudiana: A Specialty Crop for Mississippi
Stevia rebaundiana (Bertoni), a perennial shrub of the Asteraceae family, is one of the most important sources of non-caloric natural sweeteners. Stevia's plant extracts and glycosides have been used for several years in Paraguay and Brazil. Studies suggest that Stevia and its glycosides exert beneficial effects on human health, including anti-hyperglycemic and antihypertensive, properties . The objectives of this study were to evaluate Stevia's cold hardiness in Mississippi and to determine the effects of different harvest schedules on leaf production and yield of diterpene glycosides. Plants purchased from Ritchers Herbs were the source of nodal explants for in vitro clonal propagation. Rooted plantlets adapted in trays were later transplanted in the field of the University of Mississippi Biological Field Station. Plant spacing was 30 cm between plants in a row and 60 cm between rows. Drip irrigation supplied water to the field at rate of ¼ to ½ inches per week during summer. To protect plants during the winter of 2010 a plastic in a field low tunnel was used, while in 2011 plants remained uncovered during the winter. Leaf biomass production and yield of diterpene glycosides were evaluated based on three different harvest schedules: 1) Three harvests in 60 day intervals, two leaf harvests in 90-day intervals and a single harvest after 180 days of cultivation. Results revealed that leaf production harvested once a year yielded more than the yield of multiple harvests (2 and 3 harvests per growing season). A total of 13896.37 Kg per hectare of stem and leaves were obtained in a single harvest, and the glycosides productivity obtained from a single harvest (rebaudioside A (398.80 Kg/ha) and stevioside (512.21 Kg/ha) was also greater than the yields of multiple harvests (2 and 3 harvests). Acknowledgements: The authors would like to thank the USDA Agricultural Research Service Specific Cooperative Agreement No 58 – 6408 – 02 – 1-612 for the partial financial support to the first author, We also acknowledge the Foundation Coordination for the Improvement of Higher Education Personnel, of the Ministry of Education, Brazil” (CAPES) and National Counsel of Technological and Scientific Development (CNPq), for a Doctor's Degree scholarship granted to the second author. We also would like to thank Mr. Solomon Green III, Mr. Gregory Swain and Mr. Mark Baker for their help with extraction and field work. References:  Jeppesen PB, Gregersen S, et al. (2000) Metabolism, 49(2): 208 – 214.