The present study 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, adopting a completely randomized design with 4 replications. The treatments were: 5 levels of IAA (indole-3-acetic acid) namely, zero, 0.1, 0.5, 1 and 1.5 mg/L and 5 levels of PBA (Tetrahydro pyranyl benzyl adenine), which were zero, 0.5, 1, 1.5 and 2 mg/L. Analysis of variance showed that the use of the two hormones and 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 by about 12.5% by increasing IAA from 0.1 to 1.5 mg/L. The greatest relative water content (42.73% and 37.38%) was obtained with 0.5 mg/L PBA and 1.5 mg/L IAA, respectively. Combination of IAA+PBA (0.1+0 mg/L) had a positive effect on both the length of the root and seedling. The high concentration of PBA and the lowest amount of IAA had similar results in terms of plant biomass. The highest plant biomass (4.33 mg) was obtained in seeds treated with 2 mg/L of cytokinin and 0.1 mg/L of auxin. Photosynthetic pigments were also affected by these two hormones through the IAA was more effective than PBA. The finding was that auxin and cytokinin increase germination and improve the morpho-physiological indicators and thus increase the yield of Stevia.
