Bioactivity of Monoterpene Alcohols as an Indicator of Biopesticidal Essential Oils against the Root Knot Nematode Meloidogyne ethiopica

Sustainable farming practices are becoming increasingly important, due to the need for a high yielding and zero carbon agriculture. Pesticide application remains one of the most efficient methods to control phytophagous parasites in crops. Yet, the use of pesticides has been subjected to tighter regulations as they can lead to substantial ecological and human health problems. Biopesticides present a sustainable alternative based on natural products with improved biocidal properties. Essential oils (EOs) are complex mixtures of highly active compounds that have previously shown to possess successful nematicidal activities. EOs are often mainly composed of terpenoids (mono- sesqui- and a few diterpenes) and phenylpropanoids. In the present work, the antinematodal activity of four pure monoterpene alcohols, which are generally found in high amounts on EOs of some aromatic and medicinal plants, was analyzed against the root knot nematode Meloidogyne ethiopica. Antinematodal activity was studied through direct contact bioassays, by adding ca. 50 nematodes to aqueous solutions of 1 mg/mL of geraniol, linalool, menthol or α-terpineol pure compounds. Toxicity was assessed by determining nematode mobility after 24, 48, 72 and 96 h. The monoterpene alcohols induced different responses in M. ethiopica throughout the time-course study. Geraniol induced complete immobility after 48h and maintained its activity throughout, while linalool reached its peak activity at 48 h and then decreased at 72 and 96 h. Menthol and α-terpineol had the highest activity at 24 h but decreased substantially throughout the time-course study. Geraniol showed an intense and lasting antinematodal activity against M. ethiopica, suggesting that EOs rich in this compound can be used in the development of nematicidal biopesticides to integrate sustainable pest management strategies.