Background Aboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between-and withinplant signalling, however, are still poorly documented in the scientific literature. Scope Given that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between-and withinplant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions. Conclusions We conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between-and within-plant signalling.

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.

Nitrogen fertilization increases crop yield but excessive nitrate use can be a major environmental problem due to soil leaching or greenhouse gas emission. Root traits have been seldom considered as selection criteria to improve Nitrogen Use Efficiency of crops, due to the difficulty of measuring root traits under field conditions. Nonetheless, learning about mechanisms of lateral root (LR) growth stimulation or repression by nitrate availability could help to redesign root system architecture (RSA), a strategy aimed at developing plants with a dense and profound root system and with higher N uptake efficiency. Here, we explored the genetic diversity provided by natural populations of the model species Arabidopsis thaliana to identify potentially adaptive differences in biomass production and root morphology in response to nitrate availability. A core collection of 24 accessions that maximizes the genetic diversity within the species and Col-0 (the reference accession) were grown vertically on agar medium at moderate (N+) nitrate level for 6 days and then transferred to the same condition or to low (N-) nitrate concentration for 7 days. There was a major nutritional effect on the shoot biomass and root to shoot biomass ratio. The variation of the root biomass and RSA traits (primary root length, LRs number, LR mean length, total LRs length and LR densities) was primarily genetically determined. Differences in RSA traits between accessions were somewhat more pronounced at N-. Some accessions produced almost no visible LRs (Pyl-1, N13) at N-, while other produced up to a dozen (Kn-0). Taken together our data illustrate that natural variation exists within Arabidopsis for the studied traits. The identification of RSA ideotypes in the N response will facilitate further analysis of quantitative traits for root morphology.