characteristics and biological activities of characteristics and biological activities of characteristics and biological activities of characteristics and biological activities of Eucalyptus torquata Eucalyptus torquata

Eucalyptus has become one of the most widely planted genera in the world because of its tolerance to a wide range of soil types and climates, as well as for its many industrial, commercial and medicinal uses. Eucalyptus torquata Luehm. is a plantation species frequently planted in semi-arid and arid regions for its ecological, forestry, ornamental and melliferous interests. Based on literature, drought tolerance of this species was mostly directed to adaptation mechanisms. Physiological investigations reveal the importance of stomatal closure and increased solute contents suggesting that osmotic adjustment is one of the main responses to drought in E. torquata . On the other hand, it showed low sensitivity to salt stress. This paper also highlights the immense benefits of E. torquata which contains essential oils with variable chemical composition and rich essentially in 1,8-cineole, torquatone, α-pinene, trans-myrtanol, α-eudesmol, β-eudesmol, globulol, trans-pinocarveol and aromadendrene. These oils, as well as the methanol and aqueous extracts possess a wide variety of bioactivities of great importance which are particularly valuable as antibacterial and antifungal agents also have a strong toxicity against insects and mites in addition to antiproliferative and cytotoxic effects against different types of cancer cells.


Introduction Introduction Introduction Introduction
Eucalypts (Eucalyptus spp.) are endemic to Australia; however, its few species are indigenous to neighboring countries. The genus Eucalyptus comprises more than 800 species and hybrids, which includes 3 and pollen for honeybees as showing an abundant flowering of long period and good quality of pollen and nectar for the nutrition of bee; for these reasons, it is frequently planted in arid regions (Eisikowitch et al., 2012;Saadaoui et al.,2022 ).
The purpose of this study is to provide the readers with information concerning the tolerance and behavior of E. torquata under drought and salt stress, also, exploring the potency and diversity of extracts and essential oils of this species in terms of chemical composition and biological activities.
Evaluation of the tolerance Evaluation of the tolerance Evaluation of the tolerance Evaluation of the tolerance of of of of E. torquata E. torquata E. torquata E. torquata to drought and salt stress to drought and salt stress to drought and salt stress to drought and salt stress Drought and the salinization of soil are a widespread environmental problems and an important factors determining plant productivity and distribution (Teulières, 2010).For landscape applications like reclamation of dry and arid saline lands, Eucalyptus is a good choice, it's a versatile woody species that develops an extensive deep root system and presents the challenge of finding a good compromise between adaptation to specific environmental conditions and productivity (Teulières et al., 2007).

Responses to drought
Drought is the second productivity-limiting stress after cold to find subsequently biotic and abiotic stresses, it was suggested that the availability of water is the important determining factor for the distribution of Eucalyptus (Li and Wang, 2003). In fact, among 117 Eucalyptus species introduced in Tunisia, E. torquata is considered a drought-resistant species (Khouja et al., 2001;Saadaoui et al., 2017). Australian Native Plants Nursery (2015) mentioned that E. torquata is tolerant of extended dry periods (El-juhany et al., 2008), also, in Saudi Arabia it was classified among the high tolerating species to drought (El-juhany and Al Al-Shaikh, 2015). In the Mediterranean arid regions, E. torquata showed a high tolerance level and flower abundance also in the southern provinces of North Africa (Chemlali et al., 2022). Mechanisms employed for drought resilience of E. torquata were investigated by Souden et al. (2020) which reported physiological and biochemical responses of this species subjecting to a dehydration period followed by rehydration. It reported that E. torquata was less resilient to drought than E. camaldulensis. Nevertheless, common responses were shown during the dehydration phase including lowering cell water potential from -1MPa to -4.9MPa after 28 days and to -7.1MPa after 45 days of no irrigation which was restored with 88% after rewatering. In the face of water stress, lowering the water potential of the cells by the plant, help to maintain the water content of the cells and, consequently, the turgor (White et al., 2000). Other physiological responses for E. torquata are observed including the early closure of stomata which starting from -3.5MPa to prevent water loss, the net photosynthesis was decreased to achieve less than 2 μmol.m⁻ .s⁻ . The chlorophyll fluorescence parameters Fv/Fm (maximum photochemical efficiency of PSII) was decreased and after 30 days of re-watering, E. torquata restored the structural and functional integrity of its photosynthetic machinery. Changes in xylem conductivity under water deficit also showed which conducted to minimal xylem embolism for E. torquata and the value of Ψ xylem which induced 50% PLC (Ψ50) is-4.6MPa, obviously, the level of xylem cavitation decreased after rehydration (Souden et al., 2020). It has been shown also that in case of drought and/or salinity, osmotic adjustment is the key to the adaptation of plants at the cellular level this by the accumulation of organic and inorganic solutes which helps to reduce the water potential without reducing the actual water content (Sanders and Arndt, 2012). For E. torquata, water stress induced accumulation of soluble sugars (glucose and fructose) and cyclitols (pinitol, myo-inositol) for its osmotic adjustment (Souden et al., 2020). These adaptive traits are the key factor in the determination of E. torquate drought resistance.

Responses to salinity
Another major stress for plants is the salinity of soils. In fact, the exposure to salt stress triggers many common reactions in Eucalyptus species which have developed several strategies to cope with these challenges (Assareh, 2016). However, three strategies for achieving greater salt tolerance: damage prevention, homeostasis establishment and growth regulation (Zhu, 2001). How E. torquata deal with and respond to salinity stress has been reported by Balti et al. (2021) and the study showed that E. torquata was the salt-sensitive even at lower salt concentrations (80 mM NaCl) among other species such as E. gomphocephala and E. loxophleba. Salt stress induces certain biochemical and physiological changes in E. torquata, also visible symptoms mainly by the development of necrotic spots in leaves after exposure to 170 mM of NaCl for 30 days which indicates saltinduced damage at cellular level. Slower growth was not observed for E. torquata indicating the inability of growth modulating under salt stress. Changes in photosynthesis also observed, salt stress majorly affect optimal protein function in the photosynthetic electron transport chain (pETC). The chlorophyll fluorescence-based PSII-related parameters calculated showed lower values, in addition to that, a decline in chlorophyll and carotenoids contents in leaves has been observed. The K + /Na + ratio for E. torquata declined significantly than other species mainly for E. loxophleba which have the ability to selectively increase K + amounts over Na + (Balti et al., 2021). Moreover, NaCl salinity causes a significant effect on Na + , K + and Cluptake and their distribution, in this, higher levels of external Na + interfere with K + acquisition limiting plant K uptake. Therefore, one of the important physiological mechanisms for salinity tolerance is the K + selective absorbance (Nasim et al., 2008). Germination also is strongly influenced by osmotic pressure caused by salts in the soil solution (Madsen and Mulligan, 2006). Mechergui et al. (2019) reported that seeds of E. torquata were not able to germinate at up to 9, 12 and 15 g.L⁻ NaCl that means that the salinity levels influenced significantly the percentage of germination. For the responses of E. torquata to salt stress in relation to growth, it reported that this species showed low survival percentages and volume growth to age 20 years under salt water irrigation (El-Juhany and Al Al-Shaikh, 2015). All these results suggest a good drought tolerance of this forest species; however, it shows a relative sensitivity to the presence of NaCl in the growing medium and soils.
Yields of Yields of Yields of Yields of E. torquata E. torquata E. torquata E. torquata on essential oils on essential oils on essential oils on essential oils The essential oils of E. torquata may be obtained from different plant parts; however, as observed in Table1, the highest was found in the leaves whose production was much higher than that in the trunk bark. Hydro distillated leaves of E. torquata ranged 1.15-3% of essential oil. Similar essential oils yield (1.21-3.1%) has been reported for E. globulus, as the principal source of Eucalyptus oil in the world (Derwich et al., 2009;Mossi et al., 2011;Mulyaningsih et al., 2011;Harkat-Madouri et al., 2015). The geographical origin also highly affects this production; in this, good extraction yields were observed for plants from Tunisia. In fact, several studies reviewed the parameters that can influence the total essential oil content of plant including part of plant (Silva et al., 2011), geographic origin (Gilles et al., 2010;Almas et al., 2018), the seasonal variations (Silva et al., 2011), the phenological stage (Salem et al., 2018), method of extraction (Ben Hassine et al., 2010;Herzi et al., 2013;Chamali et al., 2021), rainfall and harvesting regime (Gilles et al., 2010). Chemical profiling of Chemical profiling of Chemical profiling of Chemical profiling of E. torquata E. torquata E. torquata E. torquata essential oils essential oils essential oils essential oils Essential oils obtained from Eucalyptus are usually rich in monoterpenes and in some cases sesquiterpenes. Nevertheless, the chemical profile and main components of oils from Eucalyptus varied significantly between species. Mostly, the main components were the oxygenated monoterpenes 1,8-cineole and the monoterpene hydrocarbons α-pinene with various percentages dependent on the specific species (Goldbeck et al., 2014;Ishnava et al., 2013). Other compounds also are detected as major component in Eucalyptus oils as example; limonene in E. crebra oils, citronellal in E. citriodora oils (Ghaffar et al., 2015) and p-cymene in E. oleosa (Chamali et al., 2019). In Tunisia, most of Eucalyptus species oils showed that the oxygenated monoterpenes constituted the major fraction as the 1,8-cineole was the major component (Elaissi et al., 2010;Elaissi et al., 2011a, 2011b, Elaissi et al., 2011Sebei et al., 2015;Limam et al., 2020;Ameur et al., 2021).
A wide number of terpenes have been identified in the leaves essential oil of E. torquata, using analyses by GC-FID, GC or GC-MS (Table 2). In spite of current variations of the origin of the analyzed plants, there is consistence that 1,8-cineole and α-pinene are a characteristic compound of this species. 1,8-cineole was isolated in concentrations between 11 and 70% also the α-pinene obtained with concentration between 10 and 20%. Other compounds detected such as trans-pinocarveol, α-terpineol and borneol from chemical class of oxygenated monoterepenes. The oils also contain considerable amount of the monoterpene hydrocarbons pcymene, also the aromadendrene and alloaromadendrenefrom chemical class of sesquiterepene hydrocarbons. α-eudesmol, β-eudesmol, γ-eudesmol and globulol are the main oxygenated sesquiterpenes. A high percentage of torquatone also was detected. This last compound forms a member of acylphloroglucinols which was a class of specialized metabolites with relatively high content in Eucalyptus with diverse structures and bioactivities (Singh et al., 2009;Yao et al., 2021). Torquatone was first isolated from E. torquata and E. caesia Benth growing in Australia with 25 and 50% of the essential oil fraction respectively (Bowyer and Jefferies, 1959). It derivative also from the essential oils of number of Eucalyptus species and absent in others and present with relative high concentration in E. torquata (Ghisalberti, 1996;Bignell et al., 1997aBignell et al., , 1997bElaissi et al., 2010;Yiğit Hanoğlu et al., 2022). The chemical formula of torquatone is C16H24O4; there is 4,6-trimethoxy-3,5-dimethyl-1-(3methylbutyroyl)-benzene (Menut et al., 1999; Figure 1 for E. torquata with 42% also the low percentage of sesquiterpenes hydrocarbons and oxygenated monoterpene with a low quantity of 1,8-cineole (12%) and a relative high amounts of α-pinene (10.5%), α-eudesmol (2.9%), β-eudesmol (10.1%) and γ-eudesmol (1.3%). Eucalyptus woodwardii oil had resembling chemical characteristics to E. torquata oil essentially in major compounds detected (Elaissi et al., 2010;Ben Amor, 2021). Plants cultivated in different countries produce essential oils with variable composition as can be seen from Table 2. Torquatone is detected as a major component of E. torquata leaves essential oils from Tunisia (42%), Australia (42%) and Cyprus (29%) while totally absent in oils from Iran and Morocco. The same for αeudesmol, β-eudesmol and γ-eudesmol that are not detected in Iranian species. An intra-specific variation is also recorded and explained by geographical, environmental and climatic variations which affect the chemical composition of essential oils. Also, it was proven that essential oils of different plant parts have different chemical composition ( Table 2). The trunk bark essential oil of E. torquata growing in Tunisia has a completely distinct chemical profile compared to the leaf essential oils. The 1,8-cineole was totally absent and the major constituents being the oxygenated monoterpenes (84.7%), with trans-myrtanol (73.4%) and myrtenol (4.7%) as the main components. The apocarotene cis-β-ionone and the fatty acid nonanoic acid also identified in significant percentages of 3.9% and 2.4% respectively, the sesquiterpene hydrocarbons were represented with only 2% with γ-maaliene as the main component (1.3%) (Lahmadi et al., 2021). Therefore, there are notable quantitative and qualitative differences in E. torquata essential oils compositions; it is mentioned in literature that these differences are attributed to several exogenous factors: harvest time, seasonal factors, soil composition, geographical position and the method of drying of plants. Endogenous factors are involved including genetic makeup and the ontogenetic development stage (Marzoug et al., 2011;Zandi-Sohani and Ramezani, 2015).
Since the chemical composition of the Eucalyptus essential oils is directly associated with their biological activities, the following discussion will be focused on such activities of E. torquata. The specific and different composition in E. torquata can only act on these activities.  Antimicrobial activity of E. torquata essential oils Eucalyptus essential oils endowed antimicrobial action against a large spectrum of bacteria and fungi which consist to its therapeutic properties as a promising alternative to drugs for several diseases and disorders (Zhang et al., 2010;Barbosa el al., 2016;Dhakad et al., 2018). Additionally, the possible interactions of Eucalyptus essential oils with conventional antimicrobial agents was studied that could lead to new treatment strategies involving reduced antibiotic doses and for higher therapeutic efficacy (Knezevic et al., 2016;Scazzocchio et al., 2016;Al-Qaysi el al., 2020). The bioactivity of Eucalyptus essential oils may be due to their monoterpene components; in fact, antimicrobial activity could be attributed to the presence of compounds such as 1,8-cineole, α-pinene, β-pinene and limonene (Dhakad et al., 2018). However, the interactions of different constituents may be responsible for the total bioactivity of Eucalyptus essential oils that can potentially lead to additive, synergistic, or antagonistic effects (Mulyaningsih et al., 2010).
Eucalyptus torquata essential oils marked antimicrobial activities against a large spectrum of bacteria based on agar diffusion method and the microdilution method (Table 3) the bioassays confirm that Grampositive bacteria are more sensitive compared to Gram-negative ones. Indeed, leaves, stems and flowers essential oils of E. torquata exhibited a moderate to high antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis and Bacillus subtilis with inhibition zones in the range of 10 and 22 mm of diameter and against the two bacteria Klebsiella pneumoniae and Proteus mirabilis with inhibition zones in the range of 8 and 10 mm of diameter while not active against salmonella typhi. Also, E. torquata flowers essential oil demonstrated antibacterial action against Pseudomonas aeruginosa with inhibition zone of 11mm (Ashour, 2008;Bardaweel et al., 2014) this last bacteria was resistant to essential oils obtained from several Eucalyptus species and from other plants (Elaissi et al., 2011;Wilkinson and Cavanagh, 2005). In other hand, Pseudomonas aeruginosa with Escherichia coli are resistant to leaves essential oils of E. torquata grown in Egypt while susceptible to that grown in Jordan with inhibition zones of 11 and 9 mm respectively (Ashour, 2008;Bardaweel et al., 2014). Minimum inhibitory concentration (MIC) of leaves essential oils of E. torquata from Jordan was calculated by the microdilution method, Norfloxacin 1 mg/ml was used as reference controls for antibacterial activity. The MIC values for Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeuriginosa are 198, 201, 197, 204 and 217 μg/ml respectively (Bardaweel et al., 2014).
E. torquata essential oils also cause growth inhibition of some fungal species, oils from flowers, stems and leaves of E. torquata from Egypt and Jordan exhibited a moderate to high antifungal activities against mycelial fungi Aspergillus flavus and Aspergillus nigeralso against the yeast Candida albicans. Flowers essential oil from Egypt showed the maximum zone inhibition against Aspergillus flavus and Candida albicans with inhibition zones of 17 and 15 mm respectively, while the leaves essential oil is active with inhibition zones of 10 and 14 mm respectively. Nevertheless, essential oils from Jordan are active against Aspergillus flavus and Candida albicans with inhibition zones of 10 mm and with MIC values of 198 and 192 μg/ml respectively (Ashour, 2008;Bardaweel et al., 2014).
As a result, the difference in the chemical composition of E. torquata essential oils shown previously could be the cause of the difference in their biological and therapeutic activities.
Antimicrobial activities of E. torquata extracts Hence, there is an urgent need to find alternative antimicrobial agents for the treatment of resistant pathogenic microorganisms. The use of plant-based antimicrobials has several advantages over synthetic chemicals since the lower incidence of numerous side effects, low toxicity for mammals and high degradability 9 (Raja, 2014). Eucalyptus species are known to be a rich source of bioactive compounds, including phenolic, flavonoid, terpenoids, tannins, phloroglucinol and cardiac glycosides, which had potential antimicrobial activities (Luís etal., 2016;Elansary et al., 2017;Bhuyan et al., 2017;Sabo and Knezevic, 2019). Indeed, phenolic compounds are those which contribute significantly to the antioxidant activities of plant extracts (Siramon and Ohtani, 2007;Ghaffar et al., 2015). Two studies conducted in Morocco revealed that aqueous extracts of powdered waste from E. torquata ( leaves, stems, twigs and other parts) contained total polyphenols amounts of 73.48 and 76.68 mg GAE/g DW and flavonoids content of approximately 58 mg RE/g DW in which significant antioxidant capacity has been investigated for these extracts (Bouhlali et al., 2020;Bouhlali et al., 2021). Additionally, methanol and aqueous extracts from leaves, stems and flowers of E. torquata showed antibacterial action against different medically bacteria such as Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Bacillus subtilis and Escherichia coli with different inhibition zones in the range of 7 and 25 mm, also, it marked an antifungal activity against the yeast Candida albicans with inhibition zones in the range of 9 and 14 mm of diameter (Ashour, 2008).
In another way, the growing interest in the use of natural plant products in the biological control of plant disease through the use of biological methods has been a great challenge for agriculture for a long time. In fact, Eucalyptus species possess fungicidal properties against large spectrum of phytopathogenic fungi (Zhou et al., 2016;Gakuubi et al., 2017;Abdelkhalek et al., 2020). Also, aqueous extracts from E. torquata waste (leaves, branches, twigs) showed an antifungal activity against two fungal pathogens Fusarium oxysporum f. sp. albedinis and Mauginiella scaettae in a dose dependent manner and more stronger than extracts from other plants such as Acacia cyanophylla, Cupressus atlantica, Nerium oleander and Schinus molle (Bouhlali et al., 2020;Bouhlali et al., 2021). These soil-borne fungal pathogens caused a serious threat to date palm (Phoenix dactylifera L.) in Morocco. "Bayoud" disease and inflorescence rot are the principal enemy of palm trees caused by these pathogens and researchers suggest the use of this plant to control these diseases. It reported that at every concentration tested, E. torquata extract showed the strongest inhibition activity on fungal mycelia growth of pathogens. At a dose of 4% of extract, the spore germination of Fusarium oxysporum inhibited with 79.21% after 7 days of incubation and strong sporulation reductions is shown with 44.97% of extract after 10 days of incubation (Bouhlali et al., 2020). 100% inhibition of spore germination of Mauginiella scaettae at a low concentration of 1% of E. torquata extracts after 24h of incubation and a great reduction in sporulation by 88.05% at a dose of 4%. The inhibitory effect of these extracts is related to their composition; moreover, content in polyphenols and flavonoids in aqueous extracts of E. torquata are found to be correlated with this antifungal activity as well as their antioxidant properties (Bouhlali et al., 2021). Table 3. Table 3. Table 3.

Anticancer activity
The cytotoxic effect of extracts and components isolated from different species of Eucalyptus has been studied by several researchers. Anti-tumor properties of phenolics, terpenoids (monoterpenes, sesquiterpenes, diterpenoids and triterpenoids) derived from Eucalyptus plants have been discussed by Abiri et al. (2021) which explain the broad spectrum of toxicity, antitumor properties, and mechanisms against cancerous cell lines of Eucalyptus-derived essential oil which can be a promising green anti-cancer drugs. Also, Bardaweel et al. (2014) demonstrated the cytotoxic effect of essential oils from E. torquata gorwn in Jordan which reported that it was varied and highly cell line dependent; in fact, various cytotoxicity levels have been observed on the cancer cell lines treated with essential oil after exposure time of 48 h at 37 °C based on MTT assay. It reported that the EBV-negative Burkitt's lymphoma BJAB cell and the human Burkitt's lymphoma Raji cell line are the most sensitive cell lines with IC50 values of 33 and 39 μg/ml respectively. Although, cytotoxic proprieties also observed against the human breast adenocarcinoma MCF7 cell line (IC50 values of 115 μg/mL), the human ductal breast epithelial tumor cell line T47D (IC50 values of 82 μg/mL), the human clear cell renal cell carcinoma Caki cell (IC50 values of 94 μg/mL), the human kidney carcinoma cell line A498 line (IC50 values of 87 μg/mL), the human prostate cancer PC3 cell line (IC50 values of 108 μg/mL), the human colon adenocarcinoma Caco-2 cell line (IC50 values of 108 μg/mL) and the human epithelial carcinoma HeLa cell line (IC50 values of 91 μg/mL). Also, the Lactate dehydrogenase (LDH) activity and the decrease in DNA content of cell line treated indicated that the cytotoxic activity of E. torquata essential oils probably mediated through induction of cell death by apoptosis (Bardaweel et al., 2014).
The trunk bark essential oil of E. torquata grown in Tunisia displayed significant antiproliferative effect against two human cancer cell lines: breast carcinoma cell lines MDA-MB-231 and colorectal cancer cell lines SW620 which demonstrated inhibitory effect on the tested cell lines proliferation in a dose-dependent manner after 48 h of incubation using Crystal Violet Staining (CVS) assay, the highest cytotoxic activity of essential oil is observed at 100μg/mL and it's shown that colon carcinoma cells are more sensitive against essential oils (with IC50 values of 26.71 μg/mL) than breast MDA-MB-231 (with IC50 values of 40.66 μg/mL) (Lahmadi et al., 2021). According to the protein-staining sulphorhodamine B (SRB) assay for cell growth, essential oils of E. torquata from Egypt (extracted from stem with IC50 value of 1.34 μg/mL and leaves with IC50 value of 5.22 μg/mL) have a cytotoxic effect on the Human breast adenocarcinoma cell line (MCF7) and failed to exert a considerable effect on Human hepatocellular carcinoma cell line (HEPG2) (Ashour, 2008). These studies increase the attention in exploring this species and improving the therapeutic opportunities against cancer.

E. torquata as pesticide
Attacks and infection by pests (especially weeds, pathogens and animal pests) are the largest competitor of agricultural crops that severely reduce crop productivity (Oerke, 2006). However, the excessive use of synthetic pesticide residue in food, accumulated in the environment and increasing health hazards to humans in addition to the increasing risk of pesticide resistance (Pimentel et al., 1992), is thus pertinent to explore the pesticidal activities of natural products. Eucalyptus species are known to be a rich source of bioactive compounds that allow it to act directly as natural pesticide (Radwan et al., 2000;Shukla et al., 2002;Batish et al. 2008;Anita et al., 2012;Barbosa et al., 2016;Adak et al., 2020). Absolutely, E. torquata has been shown insecticidal properties against the Cochineal, Dactylopius opuntiae, an insect that highly damaging the cactus plants in Morocco, , , , it found that three applications of aqueous extract (60%) of E. torquata leaves are needed to reduce mealybug populations also caused the death of 65% of females and 50% of nymphal stages of Dactylopius spp. after 72 h after spraying with E. torquata extract which could be an alternative for the control of wild cochineal (El Finti et al., 2022). Also, E. torquata essential oils showed a great insecticidal potential on the adults of Rhyzopertha dominica, an insect pest of stored products, in which significant fumigant toxicity against insect which was augmented by increasing the concentration of E. torquata essential oils and the exposure time. The LC50 value decreased with increasing exposure time from 37.728 (µL/L of Air) after 24 h to 31.567 (µL/L of Air) after 72 h of exposure with essential oil. In fact, sublethal biochemical disruption has been shown in treated insects, including the reduction of energy content resulting from the significant decrease of the protein and glycogen contents. In other hand, an inhibition of digestive amylase and protease enzyme activities, also, a significant decreases in the relative growth rate of insects (Ebadollahi et al., 2022) which confirm that E. torquata extract and essential oils can be used to control insect pests. Also, it found that possess acaricidal properties as reported by Ebadollahi et al. (2017) which demonstrated that E. torquata leaves essential oils have strong toxicity against the adult females of Tetranychus urticae Koch and the observed LC50 values in the fumigation test was 3.59 μL/L air after 24 h.

Conclusions Conclusions Conclusions Conclusions
With many Eucalyptus species adapted to arid conditions, E. torquata is considered drought tolerant. The corresponding tolerance mechanisms developed by this species were demonstrated in this review. To assume, drought resistance of E. torquata was manifested by stomatal closure to prevent water loss. Osmotic adjustment was a coping strategy to water stress by increasing the accumulation of solutes, including soluble sugars (glucose and fructose) and cyclitols (pinitol and myo-inositol) in addition to that, the resilience to xylem embolism. However, salt stress may have a negative impact on E. torquata which appears sensitive to the presence of NaCl that acts in particular on photosynthesis. This paper showed also the large variability in yields and chemical composition that exists among E. torquata hydro distillated essential oils from several origins. The majority of oils produced are rich in 1,8-cineole, α-pinene and torquatone. It can be concluded that E. torquata derived essential oils are a rich resource of active phytochemicals which can possess a wide range of biological activities; From the present review, it is clear that possess potent antimicrobial capacity and exhibit an advances anticancer and biocidal effects.