Positive effects of karrikin on seed germination of three medicinal herbs under drought stress

Improper seed germination is a serious challenge for medicinal herbs under drought stress conditions in semi-arid and arid regions. A new group of plant growth regulators known as karrikins have been proved useful to improve seed germination in some plants. In this regard, the effects of karrikin on seed germination and vigor of three medicinals under drought stress were examined. Seeds of Trachyspermum copticum (L.) Link, Foeniculum vulgare Miller, and Cuminum cyminum L. were sowed under drought treatments (-1, -1.5, -2 and -2.5 MPa of PEG 6000), with and without synthetic Karrikin GR24 (10µM). Results indicated increasing osmotic pressure seed germination characteristics were severely reduced; however, karrikin significantly increased the seed germination of the three herbs. The application of karrikin in all drought conditions significantly increased germination percentage, germination rate, germination index, seedling vigor, shoot length and radicle length of all herb seedlings. Ajwain (T. copticum) showed a greater drought tolerance compared to the other medicinal species.