An Uncommon Plant Growth Regulator, Diethyl Aminoethyl Hexanoate, Is Highly Effective in Tissue Cultures of the Important Medicinal Plant Purple Coneflower (Echinacea purpurea L.)

We investigated the effects of various concentrations of diethyl aminoethyl hexanoate (DA-6) on the regeneration and growth of adventitious buds in in vitro purple coneflower cultures. Among the 3 types of explants tested, leaf explants required higher concentrations of DA-6 than petiole and root explants in order to obtain high regeneration rates, while root explants required the lowest concentration of DA-6. Additionally, explants with higher ploidy levels were more sensitive to the addition of DA-6, while explants with lower ploidy levels required higher concentrations of DA-6 to achieve its maximal regeneration rate. Interestingly, the application of a concentration that was conducive to the regeneration of explants with lower ploidy levels was inhibitory to the regeneration of explants with higher ploidy levels. Moreover, during the growth of regenerated buds, DA-6 application significantly improved plant height and weight, root weight, root thickness, root number, primary root length, total root length, and root/top ratio. Differences in the responses of explants to supplementation with DA-6 were also observed among explants with different ploidy levels, with buds having lower ploidy levels responding to lower concentrations of DA-6. Taken together, the results of the present experiments showed that proper application of DA-6 could increase in vitro culture efficiency in purple coneflower.