Phytotoxic Effects of Plant Essential Oils: A Systematic Review and Structure-Activity Relationship Based on Chemometric Analyses

Abstract

Herbicides are natural or synthetic chemicals used to control unwanted plants (weeds). To avoid the harmful effects of synthetic herbicides, considerable effort has been devoted to finding alternative products derived from natural sources. Essential oils (EOs) from aromatic plants are auspicious source of bioherbicides. This review discusses phytotoxic EOs and their chemical compositions as reported from 1972 to 2020. Using chemometric analysis, we attempt to build a structure-activity relationship between phytotoxicity and EO chemical composition. Data analysis reveals that oxygenated terpenes, and mono- and sesquiterpenes, in particular, play principal roles in the phytotoxicity of EOs. Pinene, 1,8 cineole, linalool, and carvacrol are the most effective monoterpenes, with significant phytotoxicity evident in the EOs of many plants. Caryophyllene and its derivatives, including germacrene, spathulenol, and hexahydrofarnesyl acetone, are the most effective sesquiterpenes. EOs rich in iridoids (non-terpene compounds) also exhibit allelopathic activity. Further studies are recommended to evaluate the phytotoxic activity of these compounds in pure forms, determine their activity in the field, evaluate their safety, and assess their modes of action.

Prevalence of Diterpenes in Essential Oil of Euphorbia mauritanica L.: Detailed Chemical Profile, Antioxidant, Cytotoxic and Phytotoxic Activities

“…The E. aellenii showed a positive correlation with E. hirta (r=0.70), while E. caracasana showed a strong correlation with E. cotinifolia . The observed correlations among different Euphorbia species could be attributed firstly to the genetic variation and maybe ascribed also to the variation in the climatic and environmental variables [2,3] …”

“…Secondary metabolites of plants have gained great interest, due to their significant role in the treatment of various diseases with fewer side effects [1] . Essential oils have been reported to exhibit different biological activities such as sedative, anxiolytic, stress reliever, anti‐depressant, antimicrobial, anti‐inflammatory, and anticancer activities besides their nutritional and cosmetic applications [2] . Moreover, EOs have a great contribution in the agrochemical field due to their allelopathic effects on several harmful weeds which may stop and/or decrease the use of synthetic pesticides in the near future [2] .…”

“…Essential oils have been reported to exhibit different biological activities such as sedative, anxiolytic, stress reliever, anti‐depressant, antimicrobial, anti‐inflammatory, and anticancer activities besides their nutritional and cosmetic applications [2] . Moreover, EOs have a great contribution in the agrochemical field due to their allelopathic effects on several harmful weeds which may stop and/or decrease the use of synthetic pesticides in the near future [2] . Chemically, EOs compose of a complex mixture of compounds that are grouped into several classes of terpenes as mono‐, sesqui‐, and diterpenes, including oxygenated and non‐oxygenated forms, that greatly participated in the different biological activity [3] …”

A Study on the Phytotoxic Potential of the Seasoning Herb Marjoram (Origanum majorana L.) Leaves

“…The criteria for the selection of those compounds were the amount obtained and whether information was available regarding their phytotoxicity in the literature. Monoterpenes, such as 1 and 3 , were already described as phytotoxic compounds that can be found in the essential oils of several species [ 33 ]. Regarding the new compound 4 , only 2.3 mg had been obtained, which was not enough to carry out the bioassay.…”

Biochemistry of Terpenes and Recent Advances in Plant Protection

“…Studies have shown that monoterpenes, citronellal, linalool, and cineole prolong the weed germination time and also reduce their development, e.g., Cassia occidentalis . Citronellal and linalool at 110 M and 55 M concentrations, respectively, completely stifled weed germination [ 112 ]. A related study on Raphanus sativus L. and Lepidium sativum , geraniol, carvone, borneol, and citronellol conferred significant inhibitory effects on seed sprouting and radical elongation of the two species of plants [ 113 , 114 ].…”