Antifungal and phytotoxic activity of essential oil from root of Senecio amplexicaulis Kunth. (Asteraceae) growing wild in high altitude-Himalayan region

Abstract This work was aimed to evaluate the essential oil from root of medicinally important plant Senecio amplexicaulis for chemical composition, antifungal and phytotoxic activity. The chemical composition analysed by GC/GC–MS showed the presence of monoterpene hydrocarbons in high percentage with marker compounds as α-phellandrene (48.57%), o-cymene (16.80%) and β-ocimene (7.61%). The essential oil exhibited significant antifungal activity against five phytopathogenic fungi, Sclerotium rolfsii, Macrophomina phaseolina, Rhizoctonia solani, Pythium debaryanum and Fusarium oxysporum. The oil demonstrated remarkable phytotoxic activity in tested concentration and significant reduction in seed germination percentage of Phalaris minor and Triticum aestivum at higher concentrations. The roots essential oil showed high yield for one of its marker compound (α-phellandrene) which makes it important natural source of this compound. Graphical abstract


Introduction
There is a growing public concern over increased level of synthetic chemicals used to protect agricultural crops in field and processed food on market shelf. So, there is a need to search new and novel compounds of plant origin with biological activities, which lead the researchers to evaluate plant base natural products like essential oils and extracts as possible natural substitutes for conventional synthetic molecules (Cowan 1999). Essential oils are blend of secondary metabolites with a variety of functional groups giving them different biological activities (Sati et al. 2013;Ahluwalia et al. 2014;Seo et al. 2014).
The genus Senecio is distributed worldwide with more than 1500 species. Different parts of the plants of this genus have been chemically investigated and different classes of compounds with different biological activities have been reported (Yang et al. 2011;Tundis et al. 2012). The essential oil from different geographical regions from this genus has also been investigated for their chemical constituents and biological activities (Chalchat et al. 2004;Belaunde et al. 2007;Tundis et al. 2007;Nori-Shargh et al. 2008;Usta et al. 2009;Kahriman et al. 2011;Maggio et al. 2015;Sharma & Shah 2015). Senecio amplexicaulis Kunth. (Asteraceae) belongs to genus Senecio and grows wild in high-altitude Himalayan region. We report the chemical composition and biological activity from the essential oil of root of S. amplexicaulis collected from high-altitude Himalayan region (3600 m). The investigation was done keeping in mind that particular region and environmental conditions could significantly affect the chemical composition and biological activity of oil. To the best of our knowledge, this is the first report of chemical composition and biological activities from the essential oil of root from S. amplexicaulis.

Essential oil composition
The hydrodistillation of shade-dried roots yielded yellow colour essential oil (0.66% v/w). In total, 18 compounds were identified accounting for 94.70% of oil. The chemical class distribution shows that roots oil is rich in monoterpenes (Table 1). Marker constituents of the essential oil are represented by three compounds as α-phellandrene (48.57%), o-cymene (16.80%) and β-ocimene (7.61%). Sesquiterpenes hydrocarbons constituted only 11.08% of oil, while oxygenated monoterpenes were present in the least quantities (3.78%). Valencene (4.68%) was present as major constituent from sesquiterpene hydrocarbons in the oil. Earlier investigations for the chemical composition from different parts of the world are in agreement with our results showing monoterpenes as major constituents of essential oils. But there is contradicting findings between earlier and our report in marker compounds of monoterpene constituents. Our report shows α-phellandrene (48.57%) as marker compound of essential oil. Essential oil shows variability in chemical composition according to different geographical regions, plant parts and continent. Essential oil from S. graciliflorus collected from Kashmir valley in Western Himalaya was rich in α-pinene, cis-ocimene, 1,2,3-trimethylcyclohexane and β-pinene (Lone et al. 2014), while S. squalidus collected from Serbia shows p-cymene (29.3%) as marker compound (Chalchat et al. 2004). Another report shows α-pinene (48.3%) as major constituent from S. farfarifolius from Turkey region (Baser & Demirci 2004). Previously, essential oil with spathulenol/m-Cymene/1,8cineole as major components is reported for S. vernalis from Iran (Nori-Shargh et al. 2008).

Antifungal activity
The essential oil was evaluated for antifungal activity against five plant pathogenic fungi. Oil exhibited concentration-dependent inhibition of fungal growth. The essential oil shows the highest activity against Macrophomina phaseolina (EC 50 = 157.04 ± 0.25 μg/mL) and the lowest activity against Rhizoctonia solani (EC 50 = 199.27 ± 1.23 μg/mL) ( Table 2). The oil showed lower activity compared with a well-known triazole fungicide hexaconazole (4.45 ± 0.31-25.92 ± 0.40 µg/mL). El-Shazly and co-workers (2002) screened flower and leaf volatile oil of S. aegyptius against two fungi Candida albicans and A. flavus. Results showed that both oils were more active against C. albicans as compared to A. flavus. In another report, essential oil of S. pandurifolius having α-phellandrene and o-cymene as major component showed remarkable antifungal activity against C. albicans (Kahriman et al. 2011). Literature report showed that essential oils activity may be due to cell membrane disruption by lipophilic compounds (Cowan 1999). Therefore, we infer that the activity of the oil is probably related to the marker compounds or synergism/antagonism between constituents of the oil.

Phytotoxic activity
The root essential oil was evaluated in this study for the phytotoxic activity using Triticum aestivum and Phalaris minor. Oil inhibited germination of both T. aestivum (65.00 ± 1.00%) and P. minor (58.34 ± 1.52%) at 500 μg/mL compared to the control. At higher concentration (500 μg/mL), oil inhibited the shoot length and root length of both test crops. As the concentration of essential oil decreases, there was a decrease in the activity, so we can say that phytotoxicity of oil was dose dependent. In our study, oil with high percentage of monoterpene hydrocarbons showed good phytotoxicity activity. This may be due to synergistic effect between marker compounds (α-phellandrene, o-cymene and β-ocimene) or between marker compounds and other compounds with less concentration (Table 3).

Conclusion
Chemical profiling of essential oil from roots of S. amplexicaulis Kunth revealed the presence of high percentage of monoterpenes. Also, the major marker compound of the essential oil is α-phellandrene, which can be of industrial use also. Results on antifungal and phytotoxic activity show that essential oil exhibited moderate to good activity and plant can be explored as natural biocontrol agent as alternative to synthetic agents. The results are encouraging keeping in view natural origin and possible synergistic or antagonistic effects of the marker components. The essential oil or its marker compounds could be combined with other biocontrol agents and trial can be conducted to access activity under field condition.

Supplementary material
Experimental section is available as supplementary information.

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