Abstract
Background: essential oils are well known for their pharmacological effectiveness as well as their repellent, insecticide, and herbicide activities. The emergence of resistant weeds, due to the overuse of synthetic herbicides, makes it necessary to find natural alternatives for weed control. The aim of this study was to evaluate the phytotoxic effects of Eucalyptus citriodora, Lavandula angustifolia, and Pinus sylvestris, three common commercial essential oils, on weeds (Portulaca oleracea, Lolium multiflorum, and Echinochloa crus-galli), food crops (tomato and cucumber), and the invasive species Nicotiana glauca. Methods: to determine herbicidal effects, essential oils were tested at different concentrations (0.125–1 µL/mL). The index of germination and seedling length data were recorded over 14 days. Results: the in vitro assays showed that L. angustifolia with linalool (38.7 ± 0.1%), 1,8-cineole (26.5 ± 0.1%), and camphor (14.2 ± 0.1%) as the main compounds showed the most phytotoxic effects affecting seed germination in weeds and tomato, and the aforementioned invasive species. L. multiflorum was the most sensitive weed, particularly to lavender essential oil, which decreased the growth of its hypocotyl and radicle by 87.8% and 76.7%, respectively, at a dose of 1 µL/mL. Cucumber was the most resistant food crop, with no significant reduction observed in seed germination and hypocotyl growth with E. citriodora and L. angustifolia essential oils. Conclusions: lavender essential oil represents a promising candidate for the development of effective and safe herbicides in the management of L. multiflorum affecting cucumber crops.
Highlights
The particular characteristics of essential oils—natural mixtures of volatile compounds—provide them with certain pharmacological properties, including their well-known antibacterial, antioxidant, anti-inflammatory, and cancer chemoprotective effects, as well as their repellent, herbicidal, and insecticidal biological activities [1,2,3,4], which have led to valuable applications in human health, food, and cosmetics industries, and in environment and agriculture
P. sylvestris exhibited some inhibition of the early root growth of Cassia occidentalis (L.) Link. [10], and E. citriodrora essential oil affected the development of certain weeds, the seed germination of Amaranthus viridis
L.), an annual weed commonly affecting cultivated land, protected agriculture, forests, plantations, and orchards, where it competes for resources with many field crops, including cruciferous crops, potato, and tomato, among others [12]; (ii) Italian ryegrass (Lolium multiflorum Lam.), an annual to biennial poaceous species largely spread globally due to its cultivation as a pasture grass [13], which has developed considerable resistance against glyphosate and other synthetic herbicides as an acetolactate synthase (ALS) inhibitor [14,15]; and (iii) barnyardgrass (Echinochloa crus-galli (L.) Beauv.), considered one of the world’s worst weeds, affecting agricultural land and grasslands as well as irrigation channels and wetlands, being, a very serious weed in rice crops [16]
Summary
The particular characteristics of essential oils—natural mixtures of volatile compounds—provide them with certain pharmacological properties, including their well-known antibacterial, antioxidant, anti-inflammatory, and cancer chemoprotective effects, as well as their repellent, herbicidal, and insecticidal biological activities [1,2,3,4], which have led to valuable applications in human health, food, and cosmetics industries, and in environment and agriculture. Certain essential oils have already demonstrated their influence on both the seed germination and seedling growth of weeds [5,6]. The development of natural herbicides based on essential oils could decrease these negative impacts, mainly by counteracting resistant weeds, since it is difficult to develop resistance using mixtures of natural components with different mechanisms of action. In this sense, agricultural compositions, including oregano essential oil together with others belonging to the Lamiaceae family such as Lavandula, Mentha, Rosmarinus, and Salvia species, have been elaborated as natural pesticides [22]. Lemongrass essential oil (Cymbopogon citratus, Poaceae) has been included as a principal ingredient in a natural herbicide invention to control the germination and growth of weeds [23]
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