Antimicrobial and Phytotoxic Activity of Origanum heracleoticum and O. majorana Essential Oils Growing in Cilento (Southern Italy)

Abstract

There is a growing interest in a potential use of essential oils (EOs) as a replacement for traditional pesticides and herbicides. The aims of this study were to: (i) Identify the chemical composition of the two EOs derived from Origanum heracleoticum L. and O. majorana L., (ii) evaluate the in vitro antifungal activity of the EOs against some postharvest phytopathogens (Botrytis cinerea, Penicillium expansum, Aspergillus niger and Monilinia fructicola), (iii) evaluate the in vitro antibacterial activity against Bacillus megaterium, Clavibacter michiganensis, Xanthomonas campestris, Pseudomonas fluorescens and P. syringae pv. phaseolicola, (iv) evaluate the effect of both studied EOs on the spore germination percentage and their minimum inhibitory concentration (MIC) against M. fructicola, and (v) study the possible phytotoxicity of the two EOs and their major constituents, carvacrol for O. heracleoticum and terpinen-4-ol for O. majorana, against tha germination and initial radicle growth of radish, lettuce, garden cress and tomato. The two EOs demonstrated promising in vitro antimicrobial and antifungal activities against all tested microorganisms. EOs showed high inhibition of spore germination percentage at the minimal inhibitory concentration of 500 and 2000 µg/mL, respectively. Moreover, both germination and radical elongation of selected plant species were sensitive to the oils.

Thymol Chemotype Origanum vulgare L. Essential Oil as a Potential Selective Bio-Based Herbicide on Monocot Plant Species

“…In the studies where oregano EO was tested on its phytotoxic activity, we have noted different species of oregano as well as different chemotypes. The relative species analyzed were O. heracleoticum with its high content of carvacrol (77.8%), O. majorana with the chemical composition of dominant components terpinen-4-ol 29.6%, δ-2-carene 20%, and camphene 13% [5], O. onites and O. acutidens with their high content of carvacrol (66% and 87%) [27,36]. High content of carvacrol (84%) was also evaluated in oregano hybrid: O. vulgare L. ssp.…”

“…All studies focused of testing the phytotoxic activities on dicot model plant species and the results showed strong activity in each of these studies, although different EO doses were used. The herbicidal effect was evaluated on seed germination as well as on root length respective to seedling development [5,8,27,28,36,38].…”

“…Thus, the discovery of new herbicides with new MOAs is particularly urgent [2]. Based on the ecological and political press on environmental protection, there is new attention on the search for natural compounds with herbicidal and/or pesticidal effect [3][4][5]. Plants and some animals have developed specific mechanisms to protect themselves against enemies by production of secondary metabolites, which could be the source of new herbicides and/or pesticides.…”

“…The use of plant EOs as possible synthetic substitutes has attracted a high interest from many scientists all over the world [5,[10][11][12]. Volatile terpenes and EOs have been reported as regulators of germination and growth of other species in several ecosystems [13].…”

“…Karst. ; Amaranthus retroflexus L., Chenopodium album L., and Rumex crispus L.) [5,27]. Scientific studies noted potential phytotoxic effect of O. vulgare which were tested on various dicot plant species (Sinapis arvensis L., Phalaris canariensis L., Lepidium sativum and Raphanus sativus.…”