Physico-chemical properties of the oil of Cymbopogon flexuosus

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.

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.