Effect of harvest timing on leaf production and yield of diterpene glycosides in Stevia rebaudiana Bert: A specialty perennial crop for Mississippi

Stevia rebaudiana (Bertoni), a perennial herb of the Asteraceae, is one of the most important sources of non-caloric natural sweeteners. Stevia's plant extracts and glycosides have been used by indigenous cultures for centuries in Paraguay and Brazil. Several studies suggest that Stevia and its glycosides exert beneficial effects on human health, including anti-hyperglycemic and antihypertensive properties (Jeppesen et al., 2000). The objectives of this study were to evaluate Stevia's cold hardness in Mississippi and determine the effects of different harvest timing 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 in. per week during summer. To protect plants during the winter of 2010 a plastic in field low tunnel was used, while in 2011 plants remained uncovered. Leaf biomass production and yield of diterpene glycosides were evaluated based on three different harvest timings: (1) Three harvests at 60 day intervals, two leaf harvests at a 90-day interval and a single harvest after 180 days of cultivation. Results revealed that leaf production from plants harvested once a year yielded more than the yield of multiple harvests (2 and 3 harvests per growing season). A total of 13,896.37 kg per hectare of stem and leaves were harvested in a single harvest. The glycosides productivity obtained from a single harvest; rebaudioside A (398.80 kg ha−1) and stevioside (512.21 kg ha−1) was also greater than the yields of multiple harvests (2 and 3 harvests).