Abstract
Essential oils (EOs) are actively investigated as an alternative to numerous synthetic biocide products. Due to their large spectra of biological activities, the impact of EOs on non-target organisms should be characterized for biopesticide development purposes. In this study the potential phytotoxicity of Cinnamomum cassia EO (CEO) on apple trees (Malus domestica) was investigated in terms of oxidative burst (glutathione redox state) and damage (malondialdehyde). At 2%, CEO concentration the reduced glutathione leaf content drops from 269.6 ± 45.8 to 143 ± 28.4 nmol g−1FW, after 30 min, illustrating a rapid and strong oxidative burst. Regarding oxidative damage, malondialdehyde increased significantly 24 h post application to 10.7 ± 3.05 nmol g−1FW. Plant defence induction was previously suspected after trans-cinnamaldehyde (CEO main compound) application. Therefore, the elicitor potential was investigated by qRT-PCR, on the expression level of 29 genes related to major defence pathways (PR protein, secondary metabolism, oxidative stress, parietal modification). Multivariate analysis and increased expression levels suggest induction of systemic resistance. Hence, the present research illustrates the dose–dependent phytotoxicity of CEO in terms of lipid peroxidation. Transcriptional data illustrates the elicitor properties of CEO. These findings can help to design pest management strategies considering both their risks (phytotoxicity) and benefits (defence activation combined with direct biocide properties).
Highlights
Owing to their antibacterial [1], fungicidal [2], insecticidal [3], acaricidal [4], nematicidal [5] and herbicidal [6] properties, essential oils (EO) are increasingly investigated to be included in agricultural practices as biopesticides
The objective of this study is to investigate the molecular mechanisms resulting from different concentrations of Cinnamomum cassia EO application (1–2%) on young Malus domestica trees, especially the resulting oxidative burst and the potential oxidative damage
As for many other EOs it seems that foliar application of cassia EO (CEO) triggers an oxidative burst as suggested by the drastic decrease in reduced GSH and ratios observed
Summary
Owing to their antibacterial [1], fungicidal [2], insecticidal [3], acaricidal [4], nematicidal [5] and herbicidal [6] properties, essential oils (EO) are increasingly investigated to be included in agricultural practices as biopesticides. According to Dayan et al [7], the fungicidal mode of action (Moa) consists of the inhibition of synthesis of the fungal cell wall component chitin. EO physiological actions on insects suggest a neurotoxic Moa [8,9], notably through octopamine synapses, γ-aminobutyric acid (GABA) and acetylcholinesterase (AChE) inhibition [10,11]. The aforementioned biological properties make them a good alternative to synthetic pesticides. They follow the European directive (2009) of a reduced risk for human health and to the environment. Their phytotoxic properties make them suitable for weed control, but are not desirable in other application contexts. In order to enable their large-scale use in the field, their potential phytotoxicity with non-target organisms, especially crop plants from an agronomic perspective must be assayed
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