Effects of Three Essential Oils on the Growth of the Fungus Alternaria solani

The early blight of tomato disease, caused by the fungus Alternaria solani, affects the tomato plant, Lycopersicon esculentum, by causing brown leaf spots and concentric black circles on the tomato fruit. In this experiment, it was tested to see if various essential oils have any inhibitory effect on the growth of the Alternaria solani fungus and are able to replace the fungicides, such as azoxystrobin and pyraclostrobin, that are being used or have been used worldwide against the early blight of tomato disease. Three essential oils fromCarum copticum (ajowan), Zataria multiflora (Shirazi thyme), and Satureja hortensis (savory)- were tested in vitro in a 200 and 400 ppm dosage to examine their effects on the growth of A. solani. The 200 ppm dosage of Carum copticuminhibited the growth of A. solani by 99.5%, while the 400 ppm dosage allowed absolutely no growth of the fungus over the period of twelve days. The essential oils of Zataria multiflora and Satureja hortensis were not very effective on inhibiting the growth of the pathogen. The 400 ppm of Satureja hortensis even fostered the growth of the fungus. Consequently, Carum copticum can potentially replace the substances that are commercially used to treat the early blight of tomato disease.