**2. Antimicrobial, Phytotoxic Activity, and Agri-Food Applications**

Recently, the use of some EOs as alternative antimicrobial and pharmaceutical agents has attracted considerable interest from scientists worldwide [1]. In particular, Abd-ElGawad et al. [2] reviewed the phytotoxic effect of some EOs and their chemical compositions as reported in bibliographic research from 1972 to 2020. The same authors used chemometric analysis to build a structure–activity relationship between phytotoxicity and EO chemical composition. In particular, the analysis of the collected data revealed that oxygenated terpenes and mono- and sesquiterpenes play principal roles in the phytotoxicity of EOs [2].

Another important study, conducted by Abd-ElGawad et al. [3], deals with the chemical composition of EO extracted from the aerial parts of *Persicaria lapathifolia* and its free radical scavenging activity and its herbicidal effect on the weed *Echinochloa colona*. The

**Citation:** Elshafie, H.S. Plant Essential Oil with Biological Activity. *Plants* **2022**, *11*, 980. https://doi.org/ 10.3390/plants11070980

Academic Editor: Filippo Maggi

Received: 31 March 2022 Accepted: 1 April 2022 Published: 4 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

results obtained showed that the extracted EO of *P. lapathifolia* exhibited substantial allelopathic activity against the germination, seedling root, and shoot growth of the weed *E. colona* in a dose-dependent manner [3]. In addition, *P. lapathifolia* EO demonstrated promising antioxidant activity [3]. On the other hand, Abd-ElGawad et al. [4] evaluated the phytotoxic activity of EOs extracted from two ecospecies of *Pulicaria undulata* (Saudi and Egyptian) against the weeds *Dactyloctenium aegyptium* and *Bidens pilosa*. The results obtained showed that the EO of the Egyptian ecospecies showed more phytotoxic activity against *D. aegyptium* and *B. pilosa* than the Saudi ecospecies [4].

An important study conducted by Ibáñez and Blázquez [5] reviewed the agri-food applications of *Curcuma longa* L. rhizome EO. This review study focused on some interesting information regarding conventional and recent extraction methods of *C. longa* rhizome oil, their characteristics, and their suitability to be applied at the industrial scale [5].

An important study published in this Special Issue, conducted by Xylia et al. [6], evaluated the efficacy of an eco-friendly product based on rosemary and eucalyptus Eos and two different application methods (vapor and dipping) on the quality attributes of tomato fruits, and the obtained results indicated that eco-friendly products based on the studied EOs were able to maintain the quality of tomato fruits. In addition, Chrysargyris et al. [7] studied the vapor application of sage EO for maintaining tomato fruit, where the quality attributes were more affected in green fruits and were less affected red fruits. The results also showed that sage EO has a lowering effect of the total phenolics, acidity, total soluble solids, and fruit chroma, with no specific trend found in both breaker and red tomatoes.

Calvopiña et al. [8] studied the chemical analysis of a new sesquiterpene essential oil from the native Andean species *Jungia rugosa* and studied its cholinergic activity. The results showed that the volatile fraction of this EO was exclusively composed of sesquiterpenes, specially curcumene (more than 45%) and sesquiphellandrene (about 17%). This EO demonstrated weak inhibition activity against AChE.

Regarding the antimicrobial activity, Camele et al. [9] studied the potential microbicide activity of *Mentha piperita* cv. 'Kristinka' and its main constituents against some common phytopathogens (*Botrytis cinerea*, *Monilinia fructicola*, *Penicillium expansum,* and *Aspergillus niger*). The results obtained showed that the tested EO has promising antifungal activity against all tested fungi. In addition, Soliman et al. [10] studied the antifungal activity of *Mentha spicata* and *Mentha longifolia* EOs against *F. oxysporum*. The results obtained also showed that the single compounds (thymol, adapic acid, menthol, and menthyl acetate) possess antifungal effects through the malformation and degradation of the fungal cell wall [10].
