Profiling the Variability of Eucalyptus Essential Oils with Activity against the Phylum Nematoda

Abstract

The genus Eucalyptus (Myrtaceae) comprises more than 800 species, mostly native to Australia. Eucalyptus shoots essential oils (EOs) are well-known for their extremely high qualitative and quantitative variation in terpenes (mainly mono-and sesquiterpenes). These EOs have a wide range of uses, from the taxonomic characterization of populations based on the chemical profiling of EO chemotypes, to industrial applications, including pharmaceutical, agrochemical, and in food and fragrances. In this study, we reviewed the available information concerning the chemical variability of EOs from Eucalyptus spp. assayed against nematodes. Among the most active EOs, those from E. globulus, E. staigeriana, and E. citriodora were more frequently used. EO chemical composition was mainly dominated by 1,8-cineole, limonene, p-cymene, citronellal and piperitone in varying proportions. Nematicidal activity of Eucalyptus EOs was reported against animal-parasitic nematodes, including gastrointestinal nematodes (e.g., Haemonchus contortus), plant-parasitic nematodes, such as root-knot nematodes (e.g., Meloidogyne incognita and M. chitwoodi) or the pinewood nematode Bursapelenchus xylophilus, and the free-living nematode Caenorhabditis elegans. Correlation between EO qualitative and quantitative composition with its respective activity may provide valuable information on the nematicidal specificity of EOs. This knowledge can be useful for devising environmentally safer pest management strategies in the conservation of ecosystems biodiversity.

A Review of the Potency of Plant Extracts and Compounds from Key Families as an Alternative to Synthetic Nematicides: History, Efficacy, and Current Developments

“…Several species of Myrtaceae are known for the characteristic feature of harboring significant concentrations of foliar EOs ( Keszei et al, 2008 ). Many EOs from these species do not only play the natural defensive roles against pathogens, but are a resource in cosmetic and pharmaceutical industries ( Keszei et al, 2008 ; Rodrigues and Faria, 2021 ). The genus Eugenia is one of the most important genera within the family.…”

“…On the other hand, Eucalyptus is also known to contain high foliar terpene-dominated EOs which have been implicated in defensive roles against pathogens ( Elbadri et al, 2008 ; Rodrigues and Faria, 2021 ). However, Eucalyptus spp.…”

“…are also known to exhibit qualitative and quantitative variations in EO chemotype composition even among trees of the same species. The monoterpenic aldehyde citronellal, eucalyptol and the ketone piperitone from E. citriodora and E. globulus have been strongly implicated in having significant bioactivity against PPNs ( Laquale et al, 2015 ; Pandey et al, 2000 ; Rodrigues and Faria, 2021 ). Other terpenes contained in these two species are: α-pinene, β-pinene, eucalyptol, isopulegol, citronellol, citronellyl formate, β-caryophyllene, β-myrcene, α-terpinene, p- cymene, γ-terpinene, terpinen-4-ol-acetate and α-terpinyl-acetate ( D’Addabbo et al, 2020 ; Rodrigues and Faria, 2021 ).…”

“…The monoterpenic aldehyde citronellal, eucalyptol and the ketone piperitone from E. citriodora and E. globulus have been strongly implicated in having significant bioactivity against PPNs ( Laquale et al, 2015 ; Pandey et al, 2000 ; Rodrigues and Faria, 2021 ). Other terpenes contained in these two species are: α-pinene, β-pinene, eucalyptol, isopulegol, citronellol, citronellyl formate, β-caryophyllene, β-myrcene, α-terpinene, p- cymene, γ-terpinene, terpinen-4-ol-acetate and α-terpinyl-acetate ( D’Addabbo et al, 2020 ; Rodrigues and Faria, 2021 ). EOs of E. citriodora showed strong bioactivity against M. incognita , causing almost 100% mortality on exposure of J2s to a 12.5 μg/ml preparation for 8 h; and when applied in soil at a rate of 200 μg/kg soil, significantly lower numbers of eggs and J2s were recovered from tomato roots ( D’Addabbo et al, 2020 ).…”

“…Also, EOs from E. meliodora were found to contain the aromatic aldehyde benzaldehyde, which exhibits a strong nematicidal activity (EC 50/24h = 9 μg/ml) ( Ntalli et al, 2011 ). In the Cluster analysis performed by Rodrigues and Faria (2021) , EOs of E. globulus were deemed to be quite similar to EOs of other species ( E. camaldulensis , E. saligna , E. botryoides , E. polyanthemos , E. viminalis , E. cordieri , E. bosistoana , E. smithii , E. cinerea , and two unidentified Eucalyptus species). EOs of E. camaldulensis , with eucalyptol and α-pinene as the main components have already been tested and implicated in inhibiting egg hatchability, and causing mortality of J2s of M. incognita ( El-Baha et al, 2017 ).…”