Natural products have been used since ancient times by the most different people, with
the purpose of treating diseases. Brazil has the greatest plant biodiversity in the world.
The Myrtaceae family is widely used by the population. It is the target of several studies
because it presents compounds with different biological properties. This family has
around 132 genera, including the Psidium genus with approximately 64 species.
Psidium guajava stands out because it has high levels of vitamins and is traditionally
used both in food and in the treatment of diseases. Furthermore, its leaves have a high
content of essential oil with various biological activities. However, there is a lack of
work evaluating the allelopathic potential, that is, its action on plant growth and
development. In this sense, the objective of this work was to evaluate the yield,
chemical composition and allelopathic activity of the essential oil from Psidium guajava
leaves. Psidium guajava leaves were collected and subjected to hydrodistillation in the
Clevenger apparatus to extract essential oils. At the end of the extraction, the oil yield
was determined, which was 0.41%. Forty-three compounds were identified, with trans caryophyllene (13.8%) and bicyclogermacrene (12.0%) as the main constituents. The
allelopathic test was carried out in a germination chamber at 25 ºC and 12 hours of
photoperiod, using concentrations of 0.001; 0.01; 0.1 and 1% of the essential oil on 20
seeds of each crop (Lactuca sativa and Cucumis sativus). The essential oil showed a
reduction in the germination percentage, in the average germination time, in the
average germination speed and in the vigor according to the germination speed index
of lettuce seeds. For cucumber seeds, there was an induction in the percentage of
germination and a reduction in other variables.
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