USE OF ESSENTIAL OILS FOR CONTROLLING BACTERIAL ANGULAR LEAF SPOT DISEASE OF CUCUMBER
2008
Gomah A A
Activity of commercially and purified essential oils of aloes, anise, black cumin, caraway, carna-tion, cumin, fennel, garlic, jojoba, lavender, onion, rue and thyme were tested against growth of Pseudomonas syringae pv. lachrymans, caused bacterial angular leaf spot disease of cucumber, in vitro and in vivo. Three essential oils had an inhib-itory effect, based on the determination of the min-imum inhibitory concentrations (MICs 0.25-2.0%). Carnation, fennel and thyme were inhibito-ry at MIC 0.5%. The three mentioned oils showed considerable variation in the inhibitory effect by the disk diffusion method, though the recognized similarity in fumigation treatments. The greatest activity was recorded with thyme (18mm) followed by carnation (15 mm) while fennel showed the low-est effect (9mm). Soaking cucumber seeds of differ-ent cultivars in 2% emulsified oils for a period rang-ing from 0.25 to 4 hours significantly decreased the percentage of germination. Shorter duration of seed soaking, 0.25 to 0.5 hours, showed lower deleterious effect on germination and fennel oil showed greater harmful effect. In greenhouse experiments, the three oils significantly controlled the disease incidence compared to the check treatment, being more pro-nounced for thyme oil followed by fennel and carna-tion oils. Analysis of the essential oils in concern showed eugenol, dieugenol, linolenic acid, methyl chavicol (estragol), anisole and thymol, as an active ingredients.
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