Phytogenotoxicity of thymol and semisynthetic thymoxyacetic acid in pre/post emergence of model plants and weeds.

Herbicides are commonly used to control weed. However, some plants are resistant to such products. To identify less harmful herbicides, it is crucial to search for different mechanisms of action. Thymol is an easily acquired allelopathic compound, capable of producing its respective semisynthetic derivative, thymoxyacetic acid. The aim of this study was to determine the effects of thymol and thymoxyacetic acid molecules as bioherbicides in greenhouse at the concentration of 3 mmol L-1 in pre- and postemergence applications in five species: Amaranthus viridis L., Cucumis sativus L., Lactuca sativa L., Eleusine indica L., and Sorghum bicolor L. The initial seedling development and DNA changes were analyzed. These molecules were contrasting with the solvent, in the negative control, and with the glyphosate, in the positive control, promoting phytogenotoxic activities. The toxic effect of thymoxyacetic acid was more effective in preemergence and thymol's in postemergence. We also observed a reduction in the germination speed index and root growth with a negative correlation to the increase in potassium leaching. Damage to the root and shoot of the seedlings was verified at the DNA level, and the phytotoxicity of the plants treated with the herbicide glyphosate was similar to the plants treated with the natural molecules tested. The bioherbicidal effect of thymol and thymoxyacetic acid exacerbates the reduction of the environmental impact caused by the disordered and increased use of residual pesticides.

Phytocytotoxicity of volatile constituents of essential oils from Sparattanthelium Mart. species (Hernandiaceae).

The intensive application of agrochemicals in crops has negatively impacted the environment and other organisms. The use of naturally occurring compounds may be an alternative to mitigate these effects. Plants are secondary metabolite reservoirs and may present allelopathic activity, which is potentially interesting to be used in bioherbicide formulations. In this context, the present work aimed to evaluate the phytotoxic and cytotoxic effects of essential oils extracted from leaves of Sparattanthelium botocudorum and Sparattanthelium tupiniquinorum in bioassays with the plant models Lactuca sativa L. and Sorghum bicolor L. Moench. The essential oils were applied at concentrations of 3,000, 1,500, 750, 375 and 187.5 ppm. Chemical characterization of the oils was performed, and their impact on the percentage of germinated seeds, initial development of L. sativa and S. bicolor seedlings, and changes in the mitotic cycle of meristematic cells from L. sativa roots was evaluated. The major compound of the essential oils was germacrene D, followed by bicyclogermacrene, ß-elemene and germacrene A. The phytotoxicity assay showed that the essential oils of both species reduced the root and shoot growth in L. sativa and decreased the germination and shoot growth in S. bicolor. Inhibition was dependent on the tested oil concentration. In the cytotoxicity assay, a decrease in mitotic index and chromosomal and nuclear alterations were observed, which resulted from aneugenic and clastogenic action.