Effects of plant density and transplanting date on herbage, stevioside, phenol and flavonoid yield of Stevia rebaudiana Bertoni

Stevia rebaudiana Bertoni is a natural sweetener plant. The leaves of Stevia are the source of glycosides. Even more, stevia contains a high percentage of phenols, flavonoids and antioxidant activity. Planting density and transplanting date are the most important agronomical factors that may affect the quality and quantity of yield. This study was conducted in Guilan province, on the base of a split-plot field experiment in a randomized complete block design for two cultivation seasons (2009-2010 and 2010-2011). Tissue culture-derived stevia plantlets were transplanted on 15 March, 30 March and 15 April in rows 50-cm apart with an inter-row spacing of 20, 25, 35, and 50 cm. Transplanting date and spacing significantly (P < 0.05) affected plant height, herbage (leaf and stem) fresh and dry weight and also stevioside, phenol and flavonoid yield. Maximum plant height (80 cm), total fresh (2017.21 g/m2) and dry (588.69 g/m2) herbage weight, and the highest stevioside (34.51 g/m2), phenol (1.5 g/m2) and flavonoid (1.97 g/m2) yield were obtained in the 50×20 cm spacing when plants were transplanted on the 15 March.