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.

Phytophthora cinnamomi is a destructive phytopathogen responsible for crown rot, trunk canker, and root rot in over 5,000 plant species worldwide. Despite its significant impact, the molecular interactions between this oomycete and host plants are not well understood. This study aimed to investigate the physiological and molecular responses of Solanum lycopersicum (tomato) to P. cinnamomi infection. The initial defense response in tomato seeds included the production of reactive oxygen species and callose deposition. Screening of commercial tomato varieties revealed varying levels of susceptibility, with the cultivar Marmande exhibiting heightened vulnerability. Three days postinoculation, Marmande showed increased expression of genes associated with reactive oxygen species generation and biosynthesis pathways for phenylpropanoids and flavonoids. Additionally, 850 genes related to cell wall remodeling, including those involved in lignin biosynthesis and pectin methyl esterase inhibitors, were significantly upregulated. Seven days postinoculation, a stronger transcriptional response was observed, with activation of ethylene and jasmonic acid signaling pathways, whereas salicylic acid showed minimal activity. Metabolomic analysis of infected roots revealed elevated levels of metabolites linked to lycopene, flavonoids, and phenylpropanoids. Furthermore, infected roots exhibited a significant reduction in pectin levels, which was corroborated by in vitro assays showing zoospore-mediated pectin degradation. These results suggest that degradation of root pectin is a key mechanism facilitating zoospore invasion in susceptible tomato hosts. This study provides new insights into the molecular mechanisms underlying host–pathogen interactions and identifies potential targets for managing P. cinnamomi-induced diseases in crops. [ ] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .