Properties studied Plant height (cm) Oil yield (%) Colour Specific gravity at 25 ◦C Refractive index at 20 ◦C Optical rotation Saponification value Acid value Ester value Citral (%) Solubility | Observations 158–180 0.4 Light yellow 0.905 1.4721 –0.33 ◦ 42.14 6.99 35.15 68–80 90% alcohol |
Results
The leaves of Cymbopogon flexuosus (lemon grass) on hydro-distillation yielded 0.4% essential oil. The physicochemical properties of the oil are shown in Table 1 The oil exhibited broad antifungal activity, the minimum bioactive concentrations with fungistatic action (temporary inhibition) of the oil was found to be 0.1 /xl ml-1 for Alternaria alternata, 0.2 /xl ml-1 for Penicillum italicum, P. implicatum, P. minio-luteum, 0.3 /xl ml-1 for Aspergillus flavus, A. fumigatus, A. niger, A. parasiticus, Botrytis cinerea, Cladosporium cladosporioides, Colletotrichum capsici, C. falcatum, Curvu-laria lunata, Fusarium cerealis, F. culmorum, F oxysporum, F udum, Gloeosporium fructigenum, Helminthosporium oryzae, H. maydis, Penicil-lium expansum, P. digitatum, P. variable, Rhizopus nigricans and 0.4 /xl ml-1 for Phoma violacea (Table 2). The minimum bioactive concentrations with fungicidal action (permanent inhibition) of the oil was found to be 0.2 µl ml-1 for Alternaria alternata, 0.4 µl ml-1 for Aspergillus flavus, A. fumigatus, A. niger, A. parasiticus, Cladosporium cladosporioides, Colletotrichum capsici, C. falcatum, Curvularia lunata, Fusarium cerealis, F. culmorum, F. oxysporum, F. udum, Gloeosporium fructigenum, Penicillium expansum, P. italicum, P. implicatum, P. digitatum, P. minio-luteum, P. variable, and 0.5 µl ml-1 for Botrytis cinerea, Helminthosporium oryzae, H. maydis, Phoma violacea, Rhizopus nigricans (Table 2). The oil inhibited heavy doses (30 fungal mycelial disc, each of 5 mm in diameter) of inoculum at 1 µl ml-1 concentration. The bioactivity of the oil persisted up to 100 ◦C, and it did not expire even after 48 months of storage.
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The oil did not exhibit any phytotoxic effect up to 50 µl ml–1 level on fruit skin. Formulation of the oil was prepared at different concentrations (10–50 µl ml-1) in the form of fungicidal spray ‘SEB-2000’. The fungicidal spray, when tested in vivo on Malus pumilo for checking the rotting, showed complete inhibition at 20 µl ml–1 concentration by pre inoculation treatment while in post inoculation treatment 30 µl ml–1 concentration of spray solution was required for the 100 % control of rotting (Table 3). The fungicidal spray was found to be cost effective and free from any side effect.
Discussion
Although many plants belonging to different angiospermic families have been screened for their antifungal activity, Cymbopogon flexuosus belonging to the family Poaceae is reported for its antifungal activity against post harvest fungal pathogens probably for the first time. A substance may inhibit the growth of fungi either temporarily (fungi-static) or permanently (fungicidal). Essential oils obtained from the leaves of Cymbopogon martinii var. motia (Dikshit et al., 1980), Hyptis suaveolens (Pandey et al., 1982), Melaleuca leucodendron (Dubey et al., 1983) and the rhizome of Alpinia galganga (Tripathi et al., 1983) have been found to contain fungistatic activity. On the other hand there are some essential oils, Cymbopogon pendulus (Pandey et al., 1996) which have fungicidal action. However, in the present investigation the oil of C. flexuosus like those of Eucalyptus oil (Shahi et al., 1999, 2000) prove to have fungistatic action at lower concentration and fungicidal action at higher concentration.
A fungicide must not be affected by extreme temperatures. Only a few researchers have studied the effect of temperature on antifungal activity of the oils. The oil of Pepromia pellucida was reported to the active up to 80 ◦C
Table 2
Minimum bioactive concentrations of the oil of Cymbopogon flexuosus against fungal pathogens
Fungi | % mycelial growth inhibition at different concentration (µl ml–1) | ||||||||||
0.1 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.7 | 0.8 | ||||
Alternaria alternata | 100s | 100s | 100s | 100s | 100s | 100s | 100s | 100s | |||
Aspergillus flavus | 49.1 | 78.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Aspergillus fumigatus | 54.9 | 92 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Aspergillus niger | 55.1 | 88 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Aspergillus parasiticus | 41.9 | 97 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Botrytis cinerea | 44 | 87.8 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Cladosporium cladosporioides | 76.3 | 81.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Colletotrichum capsici | 83.4 | 93.1 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Colletotrichum falcatum | 69 | 76.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Curvularia lunata | 80.1 | 90.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Fusarium cerealis | 71.3 | 93.1 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Fusarium culmorum | 70 | 86.7 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Fusarium oxysporium | 73.2 | 89.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Fusarium udum | 66.7 | 76.9 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Gloeosporium fructigenum | 54.2 | 86.2 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Helmenthosporium maydis | 81 | 91.4 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Helmenthosporium oryzae | 79 | 90.2 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillium digitatum | 56.2 | 77.3 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillium expansum | 33.3 | 86.1 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillium italicum | 73 | 100s | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillium implicatum | 75.5 | 100s | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillum minio-luteum | 61 | 100s | 100s | 100s | 100s | 100s | 100s | 100s | |||
Penicillum variable | 45.5 | 76.1 | 100s | 100s | 100s | 100s | 100s | 100s | |||
Phoma violacea | 33.1 | 69.2 | 80 | 100s | 100s | 100s | 100s | 100s | |||
Rhizopus nigricans | 54.3 | 87.2 | 100s | 100s | 100s | 100s | 100s | 100s | |||
s, fungistatic action; c, fungicidal action.
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Table 3