SummaryThe effect of four monoterpenes ‐ citronellol, citronellal, cineole and linalool ‐ on the germination, growth and physiology of Cassia occidentalis was investigated. All four monoterpenes reduced germination of C. occidentalis seeds but to varying extents. Citronellal and linalool completely inhibited germination beyond the concentrations of 55 and 110 μM, respectively, whereas in response to treatment of citronellol no germination was observed beyond 330 μM. Further, the growth of seedlings, measured in terms of seedling length and biomass, was also adversely affected. A reduction in chlorophyll content of the cotyledonary leaves of C. occidentalis was also noticed, indicating an adverse effect on photosynthesis. Likewise, respiratory ability of growing seeds was also impaired in response to all four monoterpenes, clearly indicating that monoterpenes affect energy metabolism. On the basis of overall phytotoxicity, potency of monoterpenes was in the order of citronellal > linalool > citronellol > cineole. The results from this study suggest that both citronellal and linalool possess strong phytotoxic potential and can thus serve as lead molecules for the synthesis of bioherbicides.

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A study was undertaken to explore the effect of volatile oils from Eucalyptus citriodora and its major constituent citronellal against two wellknown rice pathogens Rhizoctonia solani and Helminthosporium oryzae The radial growth and dry weight of both the test fungi were drastically reduced in response to the volatile oils A complete inhibition of R solani and H oryzae was observed at 10 and 20 ppm respectively Citronellal alone was found to be more effective than eucalypt oils Based on the study it was concluded that eucalypt volatile oils have potential for the suppression of phytopathogenic fungi

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