Abstract
Naturally produced by aromatic plants, essential oils (EO) contain a wide range of volatile molecules, including mostly secondary metabolites, which possess several biological activities. Essential oils properties such as antioxidant, antimicrobial and anti-inflammatory activities are known for a long time and hence widely used in traditional medicines, cosmetics and food industries. However, despite their effects against many phytopathogenic fungi, oomycetes and bacteria as well as weeds, their use in agriculture remains surprisingly scarce. The purpose of the present review is to gather and discuss up-to-date biological activities of EO against weeds, plant pathogenic fungi, oomycetes and bacteria, reported in the scientific literature. Innovative methods, potentially valuable to improve the efficiency and reliability of EO, have been investigated. In particular, their use towards a more sustainable agriculture has been discussed, aiming at encouraging the use of alternative products to substitute synthetic pesticides to control weeds and plant diseases, without significantly affecting crop yields. An overview of the market and the recent advances on the regulation of these products as well as future challenges to promote their development and wider use in disease management programs is described. Because of several recent reviews on EO insecticidal properties, this topic is not covered in the present review.
Highlights
Plants are naturally able to produce a wide range of molecules, especially secondary metabolites, which are known to perform a function in protecting plants against pathogens, owing to their biological properties [1]
It has been demonstrated through many studies that the response of a specific phytopathogenic fungus in contact with essential oils (EO) was highly variable from one EO to another: Botrytis cinerea is inhibited by EO from black caraway and fennel, but not from peppermint [50]
Several authors previously synthesized EO herbicidal and phytotoxic properties in reviews [133,134]. These phytotoxic effects have been demonstrated for Amaranthus retroflexus, Chenopodium album and Rumex crispus being completely inhibited in contact with Origanum acutidens EO [135], for Raphanus sativus, Lactuca sativa and Lepidium sativum tested with EO of Thymus vulgaris, Verbena officinalis and Melissa officinalis [136] and for A. retroflexus, Cirsium arvense and Lactuca serriola treated with Achillea gypsicola and Achillea biebersteinii EO [137]
Summary
Plants are naturally able to produce a wide range of molecules, especially secondary metabolites, which are known to perform a function in protecting plants against pathogens, owing to their biological properties [1]. Among these molecules, more than 3000 essential oils (EO), which are complex mixtures mostly constituted of secondary metabolites, are identified and known [2]. The current overuse of synthetic pesticides, causing environment and human health negative effects and pesticide-resistant biotypes, the emergence of resistance phenomena and the pesticides’ withdrawal and restrictions (Directive 91/414/EEC, July 1993 and Regulation 1107/2009/EC, 2011) on a European and on a worldwide scale, are encouraging a reduction in pesticides’ use and the need for alternative control methods and integrated pest management (IPM) systems [9]. As insecticide use has been the most reviewed biological property, in comparison with other ones against plant pathogens, with the recent contribution of several authors on that subject [13,14,15,16,17,18,19], as well as in several book chapters [20,21,22], it is not covered in the current paper
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