Nicotiana plumbaginifolia Leaf Extracts as an Efficient Antibacterial and a Biocontrol Agent Versus Tomato Pathogenic Bacteria

Abstract

Antibacterial agents derived from plants are known as suitable alternatives for synthetic pesticides because of their health and the lack of any side effects on plants. This study aims to assess in vitro effect of water, ethanol and methanol extracts of tobacco (Nicotiana plumbaginifolia) leaves on plant pathogenic bacteria and their effect on the control of bacterial infection in tomato plant in the farm conditions. Also, effective compounds of the selected extract were characterized. Water, ethanol and methanol extracts were prepared from the leaves of Nicotiana plumbaginifolia by soaking method. Antibacterial effects of three extracts were determined by agar well diffusion method in 100, 400 and 800 mg/ml concentrations on plant pathogenic bacteria including Xantomonas campestris PTCC1473, Pseudomonas aeruginosa PTCC1181, Pseudomonas syringae PTCC1290, Enterobacter aerogenes PTCC1221, Clavibacter michiganensis PTCC1399, Ralstonia solanacearum PTCC1600 and Gluconacetobacter PTCC1734. Then the effect of the extract was analyzed on the protection of infection and some characteristics of the tomato fruit in farm conditions. For this purpose, the tomato bushes were inoculated with the bacterium that were highly sensitive to the extracts and in order to evaluate the effect of the extract on the tomato fruit characteristics, factors including pH, ascorbic acid content, lycopene content, texture stiffness and antioxidant activity of tomatoes were assessed post treatment. Effective compounds of the extract with the maximum antibacterial effect were measured using GC/MS method. Water, ethanol and methanol extracts of Nicotiana plumbaginifolia in the minimum concentration (MIC) of 400 mg/ml were effective on the most of studied bacteria and had the most effect on Pseudomonas aeruginosa PTCC1181 with the growth inhibition zone of 22.51 mm (water extract), 19.39 mm (ethanol extract) and 20.94 mm (methanol extract). The concentration of 800 mg/ml of the extracts was detected as minimum bactericidal concentration (MBC). The results showed that the methanol extract of Nicotina plumbaginifolia had the most effect on the studied bacteria without changes in plant growth indicators. GC/MS analysis of the extract approved the existence of several organic acids and antimicrobial compounds including benzoic acid, hydroxymethylfurfural, nicotine, nonanoic acid, neophytadiene and plant esters. The methanol extract of Nicotiana plumbaginifolia leaves had the greatest impact on Pseudomonas aeruginosa PTCC1181 as one of the pathogens of tomato, and this extract also controlled the growth of bacteria on the tomato plant in farm condition and this plant extract is recommended as an antimicrobial agent to control the bacterial disease of tomato.