Phytotoxicity and Plant Defence Induction by Cinnamomum cassia Essential Oil Application on Malus domestica Tree: A Molecular Approach

Essential oils (EOs) are actively investigated as an alternative to numerous synthetic biocideproducts. Due to their large spectra of biological activities, the impact of EOs on non-target organismsshould be characterized for biopesticide development purposes. In this study the potential phytotoxicityof Cinnamomum cassia EO (CEO) on apple trees (Malus domestica) was investigated in terms of oxidativeburst (glutathione redox state) and damage (malondialdehyde). At 2%, CEO concentration the reducedglutathione leaf content drops from 269.6 ± 45.8 to 143 ± 28.4 nmol g−1FW, after 30 min, illustratinga 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 previouslysuspected after trans-cinnamaldehyde (CEO main compound) application. Therefore, the elicitorpotential was investigated by qRT-PCR, on the expression level of 29 genes related to major defencepathways (PR protein, secondary metabolism, oxidative stress, parietal modification). Multivariate analysis and increased expression levels suggest induction of systemic resistance. Hence, thepresent 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 pestmanagement strategies considering both their risks (phytotoxicity) and benefits (defence activationcombined with direct biocide properties).