Effects of hydro-alcoholic extract of some medicinal plants on control of Alternaria solani fungus causing tomato early blight disease

Tomato early blight disease, caused by Alternaia solani fungus, is one of the most important diseases of tomato in the world, and also in Iran. In order to investigate the antifungal activity of some medicinal plants to control this fungus, separate experiments were conducted in a completely randomized design under in vitro and greenhouse conditions. In the first experiment, the effect of concentrations of 200, 400 and 600 ppm of hydro-alcoholic extract (70% methanol and 30% water) of Thymbra spicata L., Thymus eriocalyx (Ronniger) Jalas, Satureja khuzistanica Jamzad and Oliveria decumbents Vent. with the negative (distilled water) and positive (Daconil, 3 g l-1) controls on the growth of A. solani fungus was studied under in vitro conditions. The results of the first experiment indicated complete inhibiting of fungal colony growth in all treatments. In the second experiment, 72 hours after contamination of tomato plants with A. solani fungus in an isolated greenhouse, contaminated plants were sprayed with the above-mentioned treatments and monitored for the disease symptoms 14 days later. In the third experiment, the protective effect of the above-mentioned treatments was studied. The results of the second and third experiments showed that with an increase in the extract concentration, the inhibitory and protective effects of the treatments increased. Although all treatments reduced the disease severity compared to the control, the concentrations of 600 ppm of T. spicata, 600 ppm of T. eriocalyx and 400 ppm of T. spicata, respectively had the most effective inhibitory and protective effects on the growth of fungus studied. Therefore, the use of the above treatments is recommended as a practical method for biological control of A. solani.