Evaluation of the Activity of Estragole and 2-Isopropylphenol, Phenolic Compounds Present in <i>Cistus ladanifer</i>

A large number of studies of <i>Cistus ladanifer</i> highlight this Mediterranean shrub as a source of the phenolic compounds responsible for the allelopathic potential of this species. There are few phenolic compounds present in <i>C. ladanifer</i> that have not yet been studied. The objective of this work was to evaluate the activity of estragole and 2-isopropylphenol on filter paper and soil on monocotyledons (<i>Allium cepa</i>) and dicotyledons (<i>Lactuca sativa</i><b>).</b> The results showed that when the test was carried out on paper, the germination and the growth of the <i>L. sativa</i> was strongly inhibited by 2 isopropylphenol and estragole. 2 isopropylphenol showed an IC₅₀ on the germination of 0.7 mM and 0.1 mM on the germination rate, 0.4 mM on the size of radicle and 0.3 mM on the size of hypocotyl. Estragole showed an IC50 on the germination rate of 1.5 mM and 1.1 mM on the size of hypocotyl. The effects of these pure compounds on <i>A. cepa</i> were lower, and when the assays were performed on the soil, they were dissipated. The mixture of these compounds on <i>A. cepa</i> had 0.6 mM IC₅₀ for the length hypocotyl on paper and 1.1 mM for the length of the radicle on soil. The mixture on <i>L. sativa</i> also inhibited the length of the radicle with an IC₅₀ of 0.6 mM. On the other hand, it was also observed that estragole stimulated the growth of the <i>A. cepa</i> radicle length on soil, showing a hormetic effect with an EC₅₀ of 0.1 mM. In conclusion, it can be said that for a species to be allelopathic in nature, it is essential to verify the effect of its possible allelochemicals on the target species, on the soil in which they will exert their action and at the concentrations found in their usual environment, in addition to taking into account the interaction with other compounds present in the medium.