Molecular mechanism of Cinnamomum zeylanicum and Citrus aurantium essential oils against the root-knot nematode, Meloidogyne incognita

Abstract

The root-knot nematode Meloidogyne incognita is the most harmful and destructive nematode species due to its widespread distribution and its ability to destroy a wide range of agriculturally and economically important crops. Plant-derived essential oils (EO) are one of the promising strategies for nematode management showing high nematicidal potential. Very little is known about the molecular mechanisms activated by EOs in M. incognita. In our study, we assessed the effects of Cinnamomum zeylanicum, Citrus aurantium and the chemical nematicide Oxamyl on the mortality of M. incognita juveniles (J2) at different doses and exposure. The toxicity of C. zeylanicum and C. aurantium EOs to M. incognita J2 was largely different, peaking 94.7 and 26.7% mortality rates after a 24-hour exposure to 100 µg mL^{- 1} EO concentrations, respectively. The different nematicidal activity of the two EOs was also confirmed by their LC₅₀ values, ranging between 0.1 and 399 mg mL^{- 1} concentrations for the 24-hour treatment, respectively.The sublethal dose (0.78 µg mL^{- 1}), the concentration that does not cause mortality but still triggers physiological responses, was chosen for both EOs and Oxamyl to investigate the expression levels of Mi-ace-1, Mi-ace-2, and Mi-hsp90, involved in host finding processes, and Mi-far-1, involved in the cuticle protection, by using real time PCR. Our results reveal that C. zeylanicum is toxic at lower doses than C. aurantium. The different expression level of Mi-far-1 in J2s treated with C. zeylanicum suggests a different action mode compared to C. aurantium and Oxamyl. Understanding the action mode of these compounds at molecular level will help to develop more potent and effective nematicides safer for environment and humans.

Keywords: Mi-ace-1; Mi-ace-2; Mi-far-1; Mi-hsp90; Essential oils; Gene expression; Nematode control; Root-knot nematode; Toxicity mechanism.

Fig. 1

Relative expression of genes Mi-ace-1 (A), Mi-ace-2 (B), Mi-hsp90 (C) and Mi-far-1 (D) in Meloidogyne incognita after a 2- and 4-hour exposure to 0. 78 µg mL^− 1 solutions of Citrus aurantium, Cinnamomum zeylanicum essential oils and to a 2 ml L^− 1 water solution of Oxamyl. At each exposure time, bars marked with the same letters are not significantly different according to the Least Significant Difference Test (P ≤ 0.05).