Allelopathic, Phytotoxic, and Insecticidal Effects of Thymus proximus Serg. Essential Oil and Its Major Constituents.

Shixing Zhou,Chenpeng Zhang,Hua Shao,Nigora Kuchkarova,Caixia Han,Chi Zhang,Caixia Wei

doi:10.3389/fpls.2021.689875

Abstract

The chemical profile of Thymus proximus essential oil (EO) and its allelopathic, phytotoxic, and insecticidal activity was evaluated. Carvacrol, p-cymene, and γ-terpinene were detected as the major components of the EO, representing 85.9% of the total oil. About 50 g fresh plant material of T. proximus in a 1.5-L air tight container completely inhibited the seed germination of Amaranthus retroflexus and Poa anuua. Meanwhile, the EO exhibited potent phytotoxic activity, which resulted in 100% germination failure of both the test species when 2 mg/ml (for A. retroflexus) and 5 mg/ml (for Poa annua) oil was applied. The EO also triggered a significant insecticidal activity on Aphis gossypii with a LC50 value of 6.34 ppm. Carvacrol was identified as the main active compound responsible for both the plant suppressing effect and the insecticidal activity of the EO. Our study is the first on the allelopathic, phytotoxic, and insecticidal activity of T. proximus EO, and the determination of the responsible compound, which indicated their potential of being further explored as environment friendly biopesticides.

Highlights

Essential oils (EOs) are mixtures of plant-derived secondary metabolites that are extensively applied in food preservation and medical practices for thousands of years (Majewska et al, 2019; Suteu et al, 2020; Giunti et al, 2021)
The EO of T. proximus was obtained by the traditional hydrodistillation method using fresh aboveground plant materials
In the case of T. proximus EO, we discovered that the insecticidal activity of p-cymene, γ-terpinene, and the mixture of three major constituents was much weaker than carvacrol, which suggested that carvacrol might be the main responsible insecticidal compound in the oil

Summary

Introduction

Essential oils (EOs) are mixtures of plant-derived secondary metabolites that are extensively applied in food preservation and medical practices for thousands of years (Majewska et al, 2019; Suteu et al, 2020; Giunti et al, 2021). Many aromatic plants are known for their extraordinary ability to produce a large amount of EOs that can repel grazers, kill pests, or inhibit the growth of competing plants growing in the neighborhood (Willmer et al, 2009; Aungtikun et al, 2021; Han et al, 2021; Sousa et al, 2021). Due to these qualities, certain EOs obtained from aromatic plants, including their major constituents, have the potential to be used as environmentally compatible alternatives to synthetic pesticides and herbicides. The commercial production of pest management products based on plant EOs appears to have lagged significantly behind, indicating a major disconnect between academic research and industrial practice (Isman, 2017).

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