Plant essential oils (EOs) are gaining interest as biopesticides for crop protection. EOs have been recognized as important ingredients of plant protection products including insecticidal, acaricidal, fungicidal, and nematicidal agents. Considering the growing importance of EOs as active ingredients, the domestication and cultivation of Medicinal and Aromatic Plants (MAPs) to produce chemically stable EOs contributes to species conservation, provides the sustainability of production, and decreases the variations in the active ingredients. In addition to these direct effects on plant pests and diseases, EOs can induce plant defenses (priming effects) resulting in better protection. This aspect is of relevance considering that the EU framework aims to achieve the sustainable use of new plant protection products (PPPs), and since 2020, the use of contaminant PPPs has been prohibited. In this paper, we review the most updated information on the direct plant protection effects of EOs, focusing on their modes of action against insects, fungi, and nematodes, as well as the information available on EOs with plant defense priming effects.

Summary: Root knot nematodes (RKNs) penetrate into the root vascular cylinder, triggering morphogenetic changes to induce galls, de novo formed ‘pseudo‐organs’ containing several giant cells (GCs). Distinctive gene repression events observed in early gall/GCs development are thought to be mediated by post‐transcriptional silencing via microRNAs (miRNAs), a process that is far from being fully characterized. Arabidopsis thaliana backgrounds with altered activities based on target 35S::MIMICRY172 (MIM172), 35S::TARGET OF EARLY ACTIVATION TAGGED 1 (TOE1)‐miR172‐resistant (35S::TOE1^R) and mutant (flowering locus T‐10 (ft‐10)) lines were used for functional analysis of nematode infective and reproductive parameters. The GUS‐reporter lines, MIR172A–E::GUS, treated with auxin (IAA) and an auxin‐inhibitor (a‐(phenyl ethyl‐2‐one)‐indole‐3‐acetic acid (PEO‐IAA)), together with the MIR172C AuxRE::GUS line with two mutated auxin responsive elements (AuxREs), were assayed for nematode‐dependent gene expression. Arabidopsis thaliana backgrounds with altered expression of miRNA172, TOE1 or FT showed lower susceptibility to the RKNs and smaller galls and GCs. MIR172C−D::GUS showed restricted promoter activity in galls/GCs that was regulated by auxins through auxin‐responsive factors. IAA induced their activity in galls while PEO‐IAA treatment and mutations in AuxRe motifs abolished it. The results showed that the regulatory module miRNA172/TOE1/FT plays an important role in correct GCs and gall development, where miRNA172 is modulated by auxins.