The Effect of Auxin and Cytokinin on Some Morpho-Physiological and Germination Characteristics of Stevia (Stevia rebaudiana Bertoni)

This research was conducted to investigate the efficiency of hormonal pretreatment on increasing germination and early growth of seedling, in the seed technology laboratory of Shahed University in 2015 as a factorial experiment based on completely randomized design with 4 replications. The treatments were: 5 levels of IAA (indole-3-acetic acid) include of zero, 0.1, 0.5, 1 and 1.5 mg/L and 5 levels of PBA (Tetra hydro pyranyl ­benzyl­ adenine) include of zero, 0.5, 1, 1.5 and 2 mg/L. Analysis of variance indicated that the use of two hormones or their interactions had a significant effect on all traits such as seed germination, biomass, leaf relative water content and photosynthetic pigments. The highest percentage of germination (66.66%) was obtained in 1.5 mg/L IAA with 1 mg/L PBA. 0.5 mg/L PBA and in 0.1 mg/L IAA the longest shoot (1.28 and 1.17 cm, respectively) was obtained. Germination coefficient decreased about 12.5% by increasing IAA from 0.1 to 1.5 mg/L. The greatest relative water content (42.73% and 37.38%) obtained with 0.5 mg/L PBA and 1.5 mg/L IAA, respectively. Combination of IAA㰐 (0.1 mg/L) on the length of the root and seedling had a positive effect. The high concentrations of PBA and the lowest amount of IAA had similar results of plant biomass. The highest of plant biomass (4.33 mg) was obtained in seed treated with 2 mg/L of cytikinin and 0.1 mg/L of auxin. Photosynthetic pigments were also affected by these two hormones though the IAA was more effective than PBA. It was con­cluded that auxin and cytokinin increases germination and improves the morpho-physiological indicators and thus increase the yield of Stevia.