Abstract
Water shortage throughout the world, especially in arid regions in the later decades has led to search for alternatives to save potable fresh water. Treated wastewater (TWW) appears to be an opportunity for irrigation. However, it could represent a stress factor for plants, and influence their metabolism, changing their secondary metabolites and, consequently, their biological properties. Eucalyptus camaldulensis essential oil (EO) had been reported to possess phytotoxic activity. The main objective of this work was to compare the chemical composition and herbicidal activity of E. camaldulensis EO obtained from leaves of young plants and old trees irrigated with well water (WW) and TWW. Germination tests were performed in vitro against Amaranthus hybridus, Chenopodium album, Echinochloa crus-galli and Lolium perenne. The EOs composition was analyzed by gas chromatography and gas chromatography/mass spectrometry. A high percentage of oxygenated monoterpenes, with 1,8-cineole as main compound, was found in the EOs from leaves of young plants irrigated with both types of water. The EO from leaves of old trees irrigated with WW contained a main fraction of monoterpene hydrocarbons (45.17%) with p-cymene as principal compound. The highest herbicidal potential was shown by the EO from young plants irrigated with TWW. It completely inhibited A. hybridus and L. perenne germination, and nearly blocked the others at all concentrations assayed. It also showed strong phytotoxic activity on seedling length. The results suggest the possible use of TWW to irrigate Eucalyptus crops as it enhances the EOs herbicidal potential that could be used as natural herbicides.
 
 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
Highlights
The agricultural system is exposed to several threats that can influence crop yields and sustainability such as diseases and pests especially weeds (Vyvyan, 2002)
Chemical composition was different for each essential oil (EO): 39 compounds were identified in E. camaldulensis EO from young plants irrigated with well water (EO1), accounting for 96.01% of the total EO composition, while 35 compounds were identified for E. camaldulensis EO from young plants irrigated with treated waste water (EO2), being 94.11% of the total EO
In E. camaldulensis EOs from old trees irrigated with well water (EO3) 35 compounds were identified, representing 91.83% of the total EO composition, compounds were identified in E. camaldulensis EOs from old trees irrigated with treated waste water (EO4) defining 96.42% of the total EO
Summary
The agricultural system is exposed to several threats that can influence crop yields and sustainability such as diseases and pests especially weeds (Vyvyan, 2002). Weeds take benefit of the advantageous conditions that occur in agricultural fields and present a good adaptability to different environments. There are many methods for weed management (cultural, mechanical, chemical, biological and biotechnological) but in most cases control relies in the use of synthetic herbicides. Received in revised form: 02 Dec 2019.
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