Antifungal Effect of 27 Medicinal Plant Species Crude Extracts Against Tomato Early Blight Agent Alternaria solani

In recent years, synthetic pesticides are known to be the most effective method of the pest and disease control. However, they are not considered as a long-term solution due to the concerns associated with pesticides application such as problems of public health, environmental pollution, reduction in crop quality, toxic effect on non-target organisms and causing resistance in pest and disease agents. Nowadays, using plant secondary compounds has been increased and these compounds are used for plant protect against post and pre-harvest diseases. Therefore, considerable research to search for biocides that are environmentally safe and easily biodegradable have been carried out during last two decades. So, using extracts from plants containing natural antifungal compounds for plant disease control is considered to be one of the desirable methods for plant protection in agriculture. The main goal of this report was studying the antifungal effect of 27 medicinal plant species crude extracts against Alternaria solani were investigated. Twenty-seven medicinal plant species including Anethum graveolens, Ocimum basilicum, Quercus sp. Althaea sp.. Heracleum persicum, Cinnamomum sp., Caryophillium aromaticus, Mentha puleguim, Mentha piperita, Lavandula sp., Valerianae sp., Borago officinalis, Urtica dioica, Petroselinum sp., Salvia officinalis, Trigonella foenum-graecum, Thymus sp., Foeniculum vulgare, Pimpinella anisum, Alliuma mpeloprasum, Adiantum capillus – veneris, Viola odorata, Papaver sp., Rosa hybrida, Malva sylvestris, Artemisia dracunculus, Matricaria recutita were collected. These plants were randomly collected to increase the chance of finding plants with bioactive extracts. Each sample was cleaned, air dried in the shade and ground to a fine powder. The powdered plant materials were extracted using ethanol and water. In the ethanolic extraction, 5 g ground sample was extracted with 100 ml ethanol for 24 h by shaking on an orbital shaker at 300 rpm. Then 30 ml distilled water was added to 70 ml of the ethanolic extract and lipids were removed with 100 ml n-Hexane mixed at 250 rpm for 2 h. Finally, Ethanolic phase was concentrated using a rotary evaporator. In aqueous extraction, 5 g ground sample was extracted with 100 ml distilled, and sterilized water warmed on a magnetic hot plate. The obtained extract was filtered over Whatman No.1.Paper filter and the filtrates were collected and dried in 50 °C oven. The inhibitory effect of these extracts was examined against Alternaria solani via paper disc method. In paper disc method, each disc was loaded with 50 mg/paper disc of crude extract. The discs were dried well after loading to remove the solvent. Loaded paper discs were placed on the plate. Plates were incubated at 25°C and the radius zone of inhibition (distance between the center of the paper disc and margin of the inhibited mycelium) was recorded. The experiments were performed in four replicates. Results showed that the most inhibition on A. solani belonged to aqueous extract of, Papaver sp., Allium ampeloprasum, and Ocimum basilicum with 10.22 ± 0.22, 10 ± 0.39 and 9.87±0.17 mm inhibition, respectively. Ethanolic extract of Foeniculum vulgare had remarkable inhibitory effect against A. solani with 8.33±0.51 mm inhibitory radius zone. Results indicated the presence of antifungal compounds in different plant extracts and that was in agreement with the results reported by authors who tested the plant extracts on different plant pathogens using paper disc method. In this study, preliminary phytochemical screening of the extracts showed the different groups of components such as Alkaloids, terpenoids, flavonoids, sterols, carbohydrates and tannins. These results showed that medicinal plants can be considered as rich sources of plants with antifungal activity. Given the effect of the plant species origin and genetic diversity on chemical composition, studies screening for novel antifungal compounds in plants grown in different parts of the world are needed. Therefore, further screening of other plant species, identifying active fractions or metabolites and in vivo application of active extracts are warranted. Moreover, they could form the basis for further investigation of fractionation for finding active fractions, the effect of origin of growing on the quality and quantity of active compounds, a number of bioactive compounds in different plant parts and finally in vivo application of extracts will be considered. Medicinal plants are valuable resources of bioactive compounds that can be utilized to control phytopathogens through comprehensive studies and complementary experiments.