Search for fungitoxic potential in essential oils of Asteraceous plants
Mahendra Rai and Deepak Acharya
Department of Botany, Danielson College, Chhindwara-480 001, M.P. state, India
Fusarium oxysporum and Trichophyton mentagrophytes were tested for their sensitivity to essential oils of some plants of compositae. In vitro effect of essential oils was evaluated by disc diffusion method. The maximum inhibition was shown by oils of Tagetes erecta and T. patula followed by Cyathocline purpurea, Blumea mollis and B. balsamifera, whereas the minimum inhibition was exhibited by Ageratus conyzoides, Dahlia pinnata, and Chrysanthemum indicum. T. mentagrophytes was found to be more sensitive as compared to F. oxyxporum.
Many plants produce essential oils as secondary metabolites. But, their exact role in the life processes of the plant is unknown. A review of literature reveals that a large number of essential oils were reported to possess fungitoxic activity ( Barnes, 1963; Korta & Starzyk, 1963; Maruzzella, 1963; Hiller, 1964; Birch,1966; Korbely & Florian,1971; Garg, 1974; Zutschi et al., 1975; Overeem, 1976; Goutam et al., 1980; Jain et al.,1980; Ikram & Haq 1980,1984; Deshmukh et al.,1986; Singh et al., 1986; Kishore & Dwivedi, 1991; Jain & Agarwal, 1992; Perrucci et al., 1994; Rai et al., 1999). The most members of family Asteraceae are known to contain essential oils which usually have antifungal / cytotoxic sesquiterpene lactons.
The main object of the present investigation was to evaluate essential oils extracted from 11-plant species of family Asteraceae against Two fungi, viz.. Fusarium oxysporum (opportunistic human pathogen) and Trichophyton mentagrophytes (potential human pathogen).
Materials and Methods
The test plants
The test plants of family Asteraceae were collected from various localities of Chhindwara and suburbs. The voucher specimens of test plants, viz., A. conyzoides, B. mollis, B. balsamifera, C. axillaris, C. indicum, C. purpurea, D. pinnata, E. triplinerve, S. acmella, T. erecta and T. patula were deposited at the Department of Botany, Danielson College, Chhindwara, M.P.
Extraction of essential oils
The plant samples were shade-dried and powdered. About 200 g of each of the dried samples were subjected to hydrodistillation for 4 hours using a Clavenger apparatus in order to obtain essential oils.The test fungi
F. oxysporum, an opportunistic pathogen and T. mentagrophytes, a potential human pathogen were selected from the locally isolated human-pathogenic fungi. The pure cultures of both the test fungi were maintained on Sabouraud Glucose Agar (SGA) at 280C. One-week old cultures were washed with sterile saline and the spore suspensions were prepared by using glasswool filtration. The rate of the colony-forming units was determined and the test inocula were adjusted to 1.5 X 105 spores per ml.
The paper disc technique
Petri dishes were filled with 10 ml of SDA in aseptic conditions, and 1 ml of the spore suspension was added per plate after the medium was solidified. Sterile discs (5 mm diameter, Whatman filter paper no. 42) were soaked in essential oils upto saturation. These saturated discs were placed in the centre of the petri dishes, which were then incubated at 370C for 48 h. For each oil, triplicates were maintained. The clear inhibition zones were measured and noted.
Results and discussion
The results of the agar diffusion tests are summarized in Table1. The data suggest that the maximum inhibition of Fusarium oxysporum and Trichophyton mentagrophytes was shown by oil of flowers of Tagetes erecta and T. patula followed by Cyathocline purpurea and whole plant of Tagetes erecta, Eupatorium triplinerve and Tagetes patula (whole plant), whereas the minimum inhibition was exhibited by oil of Dahlia pinnata, Ageratum conyzoides and Chrysanthemum indicum. Similarly, Kishore & Dwivedi (1991) reported that oil of T. erecta was significantly effective against Pythium aphanidermatum. Singh et al. (1986) found that the mycelial discs of Epidermophyton floccosum, Microsporum canis and Trichophyton mentagrophytes were completely killed when dipped in oil of Ageratum conyzoides. In the present investigation, however, oil of A. conyzoides exhibited relatively low inhibitory activity which must be due to more tolerance of test fungi to the oil of A. conyzoides. Zutschi et al. (1975) first reported fungicidal activity of Caesulia axillaris. In the present studies also, oil of C. axillaris was effective against F. oxysporum and T. mentagrophytes. Both the test fungi, viz., F. oxysporum and T. mentagrophytes were much sensitive to oil of Eupatorium triplinerve, which corroborates the earlier findings with some plant pathogenic fungi (Garg, 1974; Yadav & Saini, 1990).
It was also observed that the sensitivity shown by T. mentagrophytes to oil of Blumea mollis and Eupatorium triplinerve was equal to the sensitivity exhibited by F. oxysporum to oil of Cyathocline purpurea. Similarly, F. oxysporum was equally sensitive to oils of E. triplinerve and whole plant of T. erecta. Moreover, it was also recorded that T. mentagrophytes was more sensitive to majority of the essential oils tested in the present investigation.
It can be concluded that the essential oil of both the species of Tagetes can be utilized topically on skin infections caused by T. mentagrophytes or F. oxysporum. But prior to this, detailed pharmacological studies are required. Acknowledgements
The authors wish to express their gratefulness to Professor Bertil Nordenstam, Director, the Swedish Museum of Natural History, Stockholm, Sweden for constant encouragement, and to Professor S A Brown, Principal, Danielson College, Chhindwara, M.P. state, India for providing laboratory facilities. Thanks are also due to University Grants Commission, New Delhi for financial assistance.
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