Phytotoxicity of Essential Oils: Opportunities and Constraints for the Development of Biopesticides. A Review.

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.

Epoxiconazole exposure affects terpenoid profiles of oilseed rape plantlets based on a targeted metabolomic approach.

Epoxiconazole is a broad-spectrum fungicide described as highly persistent in soil and as such can be considered as an abiotic agent like other problematic agrochemicals. Furthermore, the plant phenotyping tool involving non-invasive monitoring of plant-emitted volatile organic compounds (VOCs) may be useful in the identification of metabolic markers for abiotic stress. We therefore decided to profile the VOCs from secondary metabolism of oilseed rape through a dose-response experiment under several epoxiconazole concentrations (0, 0.01, 0.1 and 1 mg L-1). VOC collections of 35-day-old whole plantlets were performed through a dynamic headspace sampling technique under defined and controlled conditions. The plantlets grew freely within a home-made, laboratory and high-throughput glass chamber without any disturbance. Putative metabolic markers were analysed using a targeted metabolomic approach based on TD-GC-MS method coupled with data acquisition in SIM mode in order to focus on terpenes and sulphur-containing volatiles. Chromatograms of emitted terpenes were achieved accurately for the 35-day-old oilseed rape plantlets. We also analysed the presence of sulphur-containing volatiles in samples of shoot and root tissues using an innovative DHS-TD-GC-MS method, but no difference was found between qualitative profiles. Nevertheless, we demonstrated through this experiment that sesquiterpenes such as ß-elemene and (E,E)-α-farnesene are involved in epoxiconazole dose-response. In particular, (E,E)-α-farnesene could serve as a metabolic marker of fungicide exposure for oilseed rape plantlets.

A laboratory high-throughput glass chamber using dynamic headspace TD-GC/MS method for the analysis of whole Brassica napus L. plantlet volatiles under cadmium-related abiotic stress.

INTRODUCTION: The 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. OBJECTIVE: The 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. METHODOLOGY: VOCs 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. RESULTS: The new trapping method produced reliable qualitative profiles of oilseed rape VOCs. Typical emissions of monoterpenes (myrcene, limonene) and sesquiterpenes (ß-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. CONCLUSION: This 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.