Abstract
The allelopathic properties of the essential oils have been exploited because they are biodegradable natural compounds that can be used in combination or as prototypes for new bioherbicides. The objectives of this study were to chemically characterize the essential oils from B. dracunculifolia, C. bonariesis and T. diversifolia and to evaluate their allelopathic potential. The essential oils were extracted by hydrodistillation and their chemical compositions were determined by GC-MS. Allelopathic activities were determined by methods that evaluate the effects of volatile compounds and direct contact of those compounds on the seed germination and seedling vigor of lettuce. The principal constituents of the essential oil from B. dracunculifolia were limonene, trans-nerolidol and β-pinene; those in the oil from C. bonariesis were limonene, trans-β-ocimene and cis-verbenol (4.4%); and those in the oil from T. diversifolia were β-pinene, α-pinene and limonene. Minor differences in the germination and vigor of lettuce seedlings were observed when they were exposed to the volatile essential oils from the leaves of the three species of the Asteraceae family. However, upon direct contact with these oils, those of C. bonariesis presented the greatest allelopathic potential, which was attributed to its higher content of oxygenated monoterpenes.
Highlights
Essential oils are secondary metabolites produced exclusively by plant and are composed of complex mixtures of many compounds
The yields of essential oil obtained from the leaves of Baccharis dracunculifolia, Conyza bonariesis and Tithonia diversifolia were 0.8, 0.4 and 0.2%, respectively
We identified 95.2, 97.3 and 99.7% of the chemical compounds in the essential oils from fresh leaves of B. dracunculifolia, C. bonariesis and T. diversifolia, respectively
Summary
Essential oils are secondary metabolites produced exclusively by plant and are composed of complex mixtures of many compounds. According to Almeida et al (2010) [2], terpenoid compounds are considered to be important bioactive compounds involved in the defense of plant organisms, which is a reason why essential oils stand out for their allelopathic properties. In addition to this natural property, these volatile compounds do not persist in the soil and contaminate the groundwater and present little or no toxicity to mammals [3], which makes these metabolites an alternative to new synthetic herbicides. Species are very varied in appearance, being composed mainly of small herbs or shrubs comprising about 1100 genera and 25,000 species found mainly in the tropical mountain regions of South America [5]
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