**1. Introduction**

Cucurbits are an important source of income for countries in the Mediterranean basin, with a total production of nearly 3,356,669 tonnes in 2018 [1]. Squash (*Cucurbita maxima* Duchesne; *Cucurbita moschata* Duchesne) is one of the major cucurbits grown in tropical and temperate regions. *Cucurbita* spp. can be affected by a number of fungal pathogens, which can cause major economic losses [2]. The majority of these fungi are seedborne, such as gummy stem blight (with foliar symptoms) and black rot (with fruit symptoms), which are caused by *Stagonosporopsis cucurbitacearum* (Fr.) Aveskamp, Gruyter & Verkley (anamorph: *Phoma cucurbitacearum* (Fr.) Sacc.), synonym *Didymella bryoniae* (Fuckel) Rehm, and which represent serious diseases that are a major constraint to cucurbit production worldwide [2–4]. Nuangmek et al. [5] reported that losses in cantaloupe can also reach 100% under conditions conducive to *S. cucurbitacearum*. *Alternaria alternata* (Fr.) Keissl. is the

**Citation:** Moumni, M.; Romanazzi, G.; Najar, B.; Pistelli, L.; Ben Amara, H.; Mezrioui, K.; Karous, O.; Chaieb,I.; Allagui, M.B. Antifungal Activity and Chemical Composition of Seven Essential Oils to Control the Main Seedborne Fungi of Cucurbits. *Antibiotics* **2021**, *10*, 104. https://doi.org/10.3390/ antibiotics10020104

Academic Editors: Edoardo Marco Napoli and Maura Di Vito

Received: 30 December 2020 Accepted: 20 January 2021 Published: 22 January 2021

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**Copyright:** © 2021 by the authors. 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/).

agen<sup>t</sup> of leaf spot, which is a further major factor responsible for low cucurbit production. The genus *Alternaria* affects the plant seedlings, leaves, stalks, stems, flowers and fruit. Yield losses of 50% and more can occur under weather conditions that are conducive to leaf spot, and in particular temperatures of 25 to 32 ◦C associated with 40% relative humidity during the day and 95% at night [6]. Many other pathogens have been detected on cucurbits seeds, such as *Fusarium solani* [7,8], *Alternaria cucumerina* [9], *Paramyrothecium roridum*, and *Albifimbria verrucaria* [10,11].

The most important unit of the squash crop is the seed, which should be of high quality and pathogen free. The propagation of such seedborne fungi is generally controlled by chemical treatments [7,12,13]. Indeed, there have been many studies on chemical control against seedborne *S. cucurbitacearum* [14–16]. Sudisha et al. [17] reported that seed treatment with the Dithane M-45 (Mancozeb 75% WP) fungicide can reduce the incidence of gummy stem blight in muskmelon crops, although this active ingredient was recently refused approval for use in the European Union, so its use will be banned in few months. Chemical fungicides are generally adopted for disinfestation, disinfection, and protection of seeds and the emerging plantlets. However, these chemicals can also cause environmental pollution due to their high persistence in the soil and water, because of their slow biodegradability [18,19].

In recent years, alternatives to synthetic fungicides have been investigated due to the extensive use of fungicides for plant and seed treatments, the problems of pathogen resistance to fungicides that this causes, and the increased demand for organic and freeof-residue vegetables [20–23]. Natural organic compound, such as plant extracts and essential oils, are among the environmentally friendly alternatives that are being developed and tested for antifungal activities against seedborne pathogens [24]. Essential oils are a rich source of broad-spectrum antifungal plant-derived metabolites that inhibit both fungal growth and their production of toxic metabolites [25]. Tea tree essential oil contains terpinen-4-ol, 1,8-cineole, and γ-terpinene, and at 2%, it has shown potent inhibition of mycelial growth of *Fusarium graminearum, Fusarium culmorum*, and *Pyrenophora graminea* [26]. Riccioni and Orzali [27] reported that tea tree essential oil represents a source of sustainable eco-friendly botanical fungicides, because of its efficacy in the control of seedborne fungi. The genus *Cymbopogon* (Poaceae) is known for its essential oils, especially for extracts of lemongrass (*Cymbopogon citratus* (DC.) Stapf). The in vitro evaluation of the effectiveness of this essential oil on the main seedborne pathogens of cucurbits was reported previously [28–30].

The objectives of the present study were to evaluate the inhibitory effects of seven essential oils that differ in their chemical compositions and to determine what the most important compounds in these seven essential oils might be, using gas chromatography– mass spectrometry (GC-MS) analysis.
