Ecotoxicity of a new biopesticide produced by Lavandula luisieri on non-target soil organisms from different trophic levels

Plant-based biopesticides have become an eco-friendly alternative to synthetic pesticides by reducing the undesired environmental impacts and side-effects on human health. However, their effects on the environment and especially on non-target organisms have been little studied. This study analyses the ecotoxicological effects of the extract of Lavandula luisieri on soil non-target organisms from different trophic levels: the earthworm Eisenia fetida, the plant Allium cepa and a natural-soil microbial community whose taxonomy was analysed through 16S rRNA gene sequencing. The extract tested is the hydrolate -product from a semi industrial steam distillation process- of a Spanish pre-domesticated variety of L. luisieri. This hydrolate has been recently shown to have bionematicide activity against the root-knot nematode Meloidogyne javanica. A previous study showed that the main components of the hydrolate are camphor and 2,3,4,4-Tetramethyl-5-methylidenecyclopent-2-en-1-one. Hydrolate caused acute toxicity (LC₅₀ 2.2% v/v) on A. cepa, while only a slight toxicity on E. fetida (LC₅₀ > 0.4 mL/g). All the concentrations tested (from 1 to 100% v/v) caused a significant decrease in bacterial growth (LC₅₀ 9.8% v/v after 120 h of exposure). The physiological diversity of the community was also significantly altered, except in the case of the lowest concentration of hydrolate (1% v/v). The ability of soil microbial communities to use a variety of carbon sources increased for all substrates at the highest concentrations. These results show that both the plants and bacterial communities of the soil can be affected by the application of biopesticides based on these hydrolates, which highlights the need for a more detailed risk assessment during the development of plant-based products.

In vitro susceptibility of Trypanosoma brucei brucei to selected essential oils and their major components

Aiming for discovering effective and harmless antitrypanosomal agents, 17 essential oils and nine major components were screened for their effects on T. b. brucei. The essential oils were obtained by hydrodistillation from fresh plant material and analyzed by GC and GC-MS. The trypanocidal activity was assessed using blood stream trypomastigotes cultures of T. b. brucei and the colorimetric resazurin method. The MTT test was used to assess the cytotoxicity of essential oils on macrophage cells and Selectivity Indexes were calculated. Of the 17 essential oils screened three showed high trypanocidal activity (IC₅₀ < 10 μg/mL): Juniperus oxycedrus (IC₅₀ of 0.9 μg/mL), Cymbopogon citratus (IC₅₀ of 3.2 μg/mL) and Lavandula luisieri (IC₅₀ of 5.7 μg/mL). These oils had no cytotoxic effects on macrophage cells showing the highest values of Selectivity Index (63.4, 9.0 and 11.8, respectively). The oils of Distichoselinum tenuifolium, Lavandula viridis, Origanum virens, Seseli tortuosom, Syzygium aromaticum, and Thymbra capitata also exhibited activity (IC₅₀ of 10-25 μg/mL) but showed cytotoxicity on macrophages. Of the nine compounds tested, α-pinene (IC₅₀ of 2.9 μg/mL) and citral (IC₅₀ of 18.9 μg/mL) exhibited the highest anti-trypanosomal activities. Citral is likely the active component of C. citratus and α-pinene is responsible for the antitrypanosomal effects of J. oxycedrus. The present work leads us to propose the J. oxycedrus, C. citratus and L. luisieri oils as valuable sources of new molecules for African Sleeping Sickness treatment.

Antibacterial and antioxidant activity of Portuguese Lavandula luisieri (Rozeira) Rivas-Martinez and its relation with their chemical composition

Lavandula luisieri (Rozeira) Rivas-Martinez is an endemic aromatic Labiatae the Iberian Peninsula, common in semi-arid regions of southern Portugal and southwestern Spain, that produces an active antibacterial essential oil from the leaves and flowers. This work presents the study of the chemical variation in various stages of growth of leaves and flowers of L. luisieri. It has been found that the essential oils are mainly constituted by 1,8-cineol, camphor, linalool and trans-α-necrodil acetate. It was also studied the total phenol content and the antioxidant activity on leaves and flowers. The ethanol extraction from de leaves contents the highest total phenol, important factor for the antioxidant activity of the plant, extract. It has been studied too, the antibacterial activity against Escherichia coli, Salmonella spp. and Staphylococcus aureus. In accordance with the obtained results, the antibacterial activities stand out against Staphylococcus, of the oil of L. luisieri (leaves and flowers).

Nematicidal activity of essential oils and volatiles derived from Portuguese aromatic flora against the pinewood nematode, Bursaphelenchus xylophilus

Twenty seven essential oils, isolated from plants representing 11 families of Portuguese flora, were screened for their nematicidal activity against the pinewood nematode (PWN), Bursaphelenchus xylophilus. The essential oils were isolated by hydrodistillation and the volatiles by distillation-extraction, and both were analysed by GC and GC-MS. High nematicidal activity was achieved with essential oils from Chamaespartium tridentatum, Origanum vulgare, Satureja montana, Thymbra capitata, and Thymus caespititius. All of these essential oils had an estimated minimum inhibitory concentration ranging between 0.097 and 0.374 mg/ml and a lethal concentration necessary to kill 100% of the population (LC(100)) between 0.858 and 1.984 mg/ml. Good nematicidal activity was also obtained with the essential oil from Cymbopogon citratus. The dominant components of the effective oils were 1-octen-3-ol (9%), n-nonanal, and linalool (both 7%) in C. tridentatum, geranial (43%), neral (29%), and β-myrcene (25%) in C. citratus, carvacrol (36% and 39%), γ-terpinene (24% and 40%), and p-cymene (14% and 7%) in O. vulgare and S. montana, respectively, and carvacrol (75% and 65%, respectively) in T. capitata and T. caespititius. The other essential oils obtained from Portuguese flora yielded weak or no activity. Five essential oils with nematicidal activity against PWN are reported for the first time.