Geraniol and Carvacrol in Essential Oil Bearing Thymus pulegioides: Distribution in Natural Habitats and Phytotoxic Effect.

Kristina Ložienė,Vaida Vaičiulytė

doi:10.3390/molecules27030986

Abstract

Phenolic and non-phenolic chemotypes of Thymus pulegioides L. are common in Europe. Essential oils of these chemotypes, as various compositions of allelochemicals, can have different phytotoxic effects on neighboring plants in natural habitats. The aim of this study was to establish the distribution of carvacrol and geraniol in T. pulegioides, growing wild in Lithuania, and compare phytotoxity of essential oils of carvacrol and geraniol chemotypes on selected plant species. In investigating 131 T. pulegioides habitats, essential oils were isolated by hydrodistillation and analyzed by GC-FID and GC-MS. Phytotoxity of essential oils extracted from carvacrol and geraniol chemotypes transmitted through water and air to selected plants was determined under laboratory conditions. Pharmacologically valuable Hypericum perforatum L. and the important forage grass Phleum pratense L. were respectively selected for experimentation from among 35 medicinal plants and 10 feed Poaceae species, growing in T. pulegioides habitats. Field results showed that carvacrol is common throughout Lithuania’s territory, whereas the geraniol is predominantly located under the continental climatic conditions of the eastern region of the country. In the laboratory experiment, it was established that there was stronger inhibition of P. pratense seed germination by the essential oil of the geraniol chemotype than the carvacrol chemotype. None of the H. perforatum seeds germinated after exposure to the essential oil of the geraniol chemotype. In general, this study builds on previous studies by providing further evidence that different T. pulegioides chemotypes have contrasting phytotoxic effects on neighboring plants within their natural habitats.

Highlights

Species of the genus Thymus (Lamiaceae) are aromatic, essential oil-bearing plants with characteristic intraspecific chemical polymorphism among chemotypes classified on the basis of the chemical composition of their essential oils [1]
Carvacrol was found in almost all habitats (Table 1, Figure 1); in most habitats, the percentage of this phenol varied from 5% to 25% (N = 99) and only in 14 habitats amounted to 14% or 30% higher (Table 1)
Published data indicate that the Thymus vulgaris geraniol chemotype is more resistant to low temperature and greater temperature amplitude during winter, whereas the carvacrol chemotype is more widely distributed where the winters are milder [26,27,28]

Summary

Introduction

Species of the genus Thymus (Lamiaceae) are aromatic, essential oil-bearing plants with characteristic intraspecific chemical polymorphism among chemotypes classified on the basis of the chemical composition of their essential oils [1]. This phenomenon has practical benefits because these chemotypes have different taste, antimicrobial, antioxidant, and flavoring properties which extend the application of oil extracts from Thymus spp. in food, pharmaceutical, and cosmetics industries [2,3,4,5]. They are biologically active compounds which are used in various industries, e.g., commercially important geraniol is characterized by antimicrobial (against foodborne and human pathogens), antioxidant, anti-inflammatory properties, is used in cosmetic and non-cosmetic products as an aromatic ingredient, an added as a flavoring agent in the beverage and food industries [14,15]; the monoterpenic phenol carvacrol has a wide spectrum of antimicrobial and antioxidant activity, and is widely usable in food production and pharmaceutical industries [16,17]

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