B1OLOGIA PLANTARUM (PRAHA) 33 (6):475-483, 1991 Allelopathic Impact of Volatile Components from Eucalyptus on Crop Plants R. K. KOHLI and DALJIT SINGH Allelopathy Research Laboratory, Department of Botany, Panjab University, Chandigarh - 160 014, India Abstract. The effect of crude volatile oils from the leaves of Eucalyptus globulus and E. citriodora and the pure terpenes - cineole and limonene from these oils, (in vapour form) was studied on Phaseolus aureus, Lens esculentum, Hordeum vulgare and Arena sativa. The parameters like germination of seeds, seedling growth, values of cell survival, and content of water and chlorophyll of the crops formed the system of bioefficacy study. The allelopathic impact of the oil vapours from the eucalypt tree becomes evident from the negative response of the parameters studied. The impact of the E. citriodora oil vapours compared to that of E. globulus oil or the pure terpenes was seen to be relatively greater in almost all parameters under investigation. A strong reciprocal correlation that exist between the concentration and the seedling growth or the water content of the crops under study supports the dose linked allelopathic phenomenon. It is suggested that oil vapours of Eucalyptus exert their effect through impairing the respiratory as well asphotosynthetic ability of the target plants. Eucalyptus is alleged to discourage the growth of other plants under its canopy, in spite of enough light, space, nutrients and soil humidity (Del Moral 1970). Relatively very low density and diversity of vegetation under 7 year old Eucalyptus tereticornis plantation compared to that of Grevillea robusta has been demonstrated by Bhaskar and Dasappa (1986). A1-Mousawi and A1-Naib (1975) reported paucity of herbaceous vegetation under E. microtheca, a-pinene, 13-pinene, camphene, and cineole (A1-Mousawi and AI-Naib 1976) and phenolic acids (AI-Naib and AI-Mousawi 1976) have been proposed to be the substances responsible for the inhibitory action. The allelochemic caused inhibition of vegetational composition, and density is well documented by Muller (1966). The leaves of Eucalyptus are intensely aromatic releasing a number of volatile terpenes into the environment (Muller and Muller 1964, Del Moral and Muller 1970). Baker (1966) evidenced the inhibition of the growth of radicles of Cucumis sp. by volatile oils of E. globulus. Essential oils from Eucalyptus have been shown to affect the diffusibility and transpiration of leaves of other plants (Polov~t and Vicherkov/t 1986, Vicherkov/t and Polov/t 1986). The volatiles from Received July 28, 1989; accepted November 11, 1990 475