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<span>One of the important aspects of hybridization is to understand the interaction between hybrid plants and the pests and diseases of the parental taxa. The foliar chemical attributes were compared between the hybrid of </span><em>Eucalyptus citriodora</em><span> and </span><em>E. torelliana</em><span> and its parental taxa. The fungus, </span><em>Cylindrocladium quinqueseptatum</em><span>, to which the hybrid and one parent </span><em>E. torelliana</em><span> have been observed resistant in the field, was used to examine patterns of resistance in relation to foliar constituents found active in labo-ratory bioassays. Concentration of active constituents of the hybrid was higher (monoterpenes- a-pinene, ß-pinene and citronellal, and total phenolics) than either parent or equivalent (ursolic acid) to parent E. torelliana thus suggesting an resistance pattern of hybrid. Beta-pinene, ursolic acid and total phenolics were found to be heritable. The findings suggest a chemical basis for fungal resistance and also indicate that the constituents could be used for screening of the disease resistant progeny in this tree system. </span>