The extensive use of chemical pesticides leads to risks for both the environment and human health due to the toxicity and poor biodegradability that they may present. Farmers therefore need alternative agricultural practices including the use of natural molecules to achieve more sustainable production methods to meet consumer and societal expectations. Numerous studies have reported the potential of essential oils as biopesticides for integrated weed or pest management. However, their phytotoxic properties have long been a major drawback for their potential applicability (apart from herbicidal application). Therefore, deciphering the mode of action of essential oils exogenously applied in regards to their potential phytotoxicity will help in the development of biopesticides for sustainable agriculture. Nowadays, plant physiologists are attempting to understand the mechanisms underlying their phytotoxicity at both cellular and molecular levels using transcriptomic and metabolomic tools. This review systematically discusses the functional and cellular impacts of essential oils applied in the agronomic context. Putative molecular targets and resulting physiological disturbances are described. New opportunities regarding the development of biopesticides are discussed including biostimulation and defense elicitation or priming properties of essential oils.

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IntroductionThe dynamic headspace sampling technique using thermal desorption, gas chromatography‐mass spectrometry (TD‐GC/MS) is a powerful method for analysing plant emissions of volatile organic compounds (VOCs), and experiments performed in sterile and controlled conditions can be useful for VOC metabolism investigations.ObjectiveThe main purpose of this study was to set up a laboratory high‐throughput glass chamber for whole plant volatiles analysis. Brassica napus L. plantlets were tested with the developed system to better understand the relationship between low emission of induced terpene and cadmium (Cd)‐related abiotic stress.MethodologyVOCs emitted by 28‐day‐old Brassica napus L. plantlets cultivated in vitro were trapped with our device using adsorbent cartridges that were desorbed with a thermal desorption unit before cryofocusing with a cooled injection system and programmable temperature vaporising inlet into an HP‐5 ms GC column. Terpene detection and quantitation from chromatogram profiles were acquired using selected ion monitoring (SIM) mode during full scan analysis and mass spectra were obtained with a quadrupole‐type mass spectrometer.ResultsThe new trapping method produced reliable qualitative profiles of oilseed rape VOCs. Typical emissions of monoterpenes (myrcene, limonene) and sesquiterpenes (β‐elemene, (E,E)‐α‐farnesene) were found for the different concentrations tested. One‐way analysis of variance for quantitative results of (E,E)‐α‐farnesene emission rates showed a Cd concentration effect.ConclusionThis inexpensive glass chamber has potential for wide application in laboratory sterile approach and replicated research. Moreover, the non‐invasive dynamic sampling technique could also be used to analyse volatiles under both abiotic and biotic stresses.

Epoxiconazole like others triazole fungicides are known to be persistent in the soil. Several studies using foliar application experiments demonstrated the effect of its triazole metabolite as plant growth regulator through the anti-gibberellin activity. And notably, the reduction of Brassica napus L. growth can be attributed to the inhibition of gibberellin biosynthesis at the stage of conversion of ent-kaurene to entkaurenoic acid. We describe here an in vitro experiment studying the relationship between epoxiconazole in culture medium (0 mg L⁻¹, 0.120 mg L⁻¹ and 0.200 mg L⁻¹) and the phenotyping (root and shoot growth) of three varieties of winter rapeseeds (Brassica napus L. var. Catalina, var. ES Astrid and var. Toccata). Plantlets fungicide content was quantified using the QuEChERS extraction method following by an automated UHPLC-MS/MS analysis. Results showed that the shoots and roots growth of Brassica napus L. plantlets was significantly inhibited by epoxiconazole at 0.120 mg L⁻¹ independently of the variety. The concentration of 0.200 mg L⁻¹ leaded to necrosis and anthocyanosis symptoms and can be considered as lethal for in vitro growing explants. The huge epoxiconazole absorption by rapeseed plantlets clearly showed a dose-dependent relationship and was closely similar for the three varieties.

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