Chemical composition and antifungal activity of essential oils from medicinal plants of Kazakhstan

Abstract The composition of essential oils from leaves of Kazakhstan medicinal plants was analysed by GC-MS. The major compounds identified were 1,8-cineole (34.2%), myrcene (19.1%) and α-pinene (9.4%) in Ajania fruticulosa; 1,8-cineole (21.0%), β-thujone (11.0%), camphor (8.5%), borneol (7.3%) and α-thujone (6.5%), in Achillea nobilis; camphor (47.3%), 1,8-cineole (23.9%), camphene (9.8%) and β-thujone (6.0%) in Artemisia terrae-albae; 1,8-cineole(55.8%) and β-pinene (6.2%) in Hyssopus ambiguus; α-thuyene(46.3%) and δ-cadinene(6.3%) in Juniperus sibirica; sabinene (64%) in Juniperus sabina; and α-pinene (51.5%), β-phellandrene (11.2%) and δ-cadinene (6.3%) in Pinus sibirica. The essential oils did not show antifungal effect (MIC > 1.20 mg/mL) on Aspergillus carbonarius and Aspergillus niger, while the oils from A. nobilis, A. terrae-albae, H. ambiguus and J. sabina exhibited moderate and moderate to weak antimicrobial activities on Fusarium verticillioides (MIC = 0.60 mg/mL) and Fusarium graminearum (MIC = 0.60–1.20 mg/mL), respectively. A principal component analysis associated the antifungal activity (r2 > 0.80, p = 0.05) with the presence of borneol, camphor, camphene, 1,8-cineole,α- and β-thujone, and of the oxygenated monoterpenes.


Introduction
The Kazakhstan flora is rich in aromatic plants (Sampietro et al. 2016). It includes Asteraceae species such as Ajania fruticulosa, Artemisia terrae-albae and Achillea Nobilis, Lamiaceae herbs like Hyssopus ambiguus, Cupressaceae shrubs such as Juniperus Sabina and Juniperus sibirica, and Pinaceae trees such as Pinus sibirica. Traditional uses of the aerial parts of these plants suggest that they exert antimicrobial activities. For example, A. fruticulosa is used against tuberculosis (Shatar et al. 2010), several Achillea species are used for wound healing (Karamenderes et al. 2007;Venditti et al. 2014Venditti et al. , 2016 and some Artemisia species are natural antiseptics (Kapustina et al. 2001;Ornano et al. 2016). Juniperus sabina is used to treat diarrhoea (Adams et al. 2006) while J. sibirica is utilised against urinary and kidney infections, pneumonia and dysentery (Efremov et al. 2012). P. sibirica is used to treat liver and kidney disorders (Shatar & Adams 1996). The antifungal activity of the oils produced by these plants remains largely unexplored. As part of a systematic search for plant antifungals, the aim of this work was to establish the chemical composition of essential oils extracted from leaves of native species from Kazakhstan and their antifungal activity against toxigenic strains of Fusarium and Aspergillus.
All our essential oils were tested against strains of F. verticillioides, F. graminearum, A. niger and A. carbonarius. Both Aspergillus strains were insensitive to the essential oils (Table S2). Although all the oils reached the IC 50 on the Fusarium species, only those of A. nobilis, A. terrae-albae, H. ambiguus and J. sabina completely suppressed fungal growth with MIC values that indicated moderate (0.10 mg/mL < MIC ≤ 1.00 mg/mL) and weak (MIC > 1.00 mg/ mL) antifungal activity (Pandini et al. 2015). A principal component analysis was performed with the percentages of the major constituents of the oils and the MIC values obtained for the Fusarium species. It revealed an inverse correlation (r 2 > 0.80, p = 0.05) between the content of some constituents (borneol, camphor, camphene, 18-cineole, α and β-thujone, and the whole content of oxygenated monoterpenes) and the MIC values. This is visualised by the obtuse angles formed between each vector of the mentioned constituents and the vectors of the MIC values observed in the biplot of component 1 vs. component 2 ( Figure S1).

Conclusions
The leaf oils of A. nobilis, A. terrae-albae, H. ambiguus and J. sabina displayed moderate or weak antifungal activity on the Fusarium strains tested. The antifungal activity was explained by the contents of camphene, borneol, camphor, 18-cineole, αand β-thujone, and the whole content of oxygenated monoterpenes.

Supplementary material
Experimental details, Figure S1 and Tables S1-S2 are available online.

Disclosure statement
No potential conflict of interest was reported by the authors.