Effective techniques to break seed dormancy and stimulate seed germination in Rheum ribes L

Rheum ribes is a plant species in Polygonaceae family which grows in Iran and is considered as a valuable medicinal species in traditional medicine. Rheum ribes seeds hardly germinate because of seed dormancy and may cause difficulties for its massive industrial cultivations. This study was performed to determine the best treatment for seed dormancy breaking. To achieve this goal, several treatments were applied comprising: Hot water (70 and 90 ˚C) for 15 minutes, moist chilling (at 2 ˚C) for 5, 10, 15, 20 and 25 days, sulfuric acid 75% (5 and 15 minutes), KNO3 (0.2%), gibberellic acid, kinetin, auxin (100, 250, 500 and 1000 ppm) and 24-epibrassinolid (0.5 and 1 ppm), for 24 and 48 h washing (for 24 and 48 h), and finally a combined treatment of gibberellic acid (500 ppm) and chilling at 2 ˚C for 5, 10, 15, 20 and 25 days. According to the results, seed dormancy in Rheum ribes is physiological since the highest germination percentage (96%) was obtained by using the combined treatment of gibberellic acid (500 ppm) and pre-chilling (for 25 days). In addition, the effect of moist chilling treatment –by itself- on breaking seed dormancy was remarkable in this plant as germination increased up to 89%. Effects of hormones were also statistically significant on increasing seed germination but compared with the salient effect of combined chilling and gibberellic acid treatment was not so remarkable. On the other hand, other applied treatments had no effects on breaking seed dormancy in Rheum ribes which indicates that the type of seed dormancy in Rheum ribes is not physical or due to the accumulation of inhibitory substance in seed coat.