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

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 Viv.) 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 N. plumbaginifolia by soaking method. Antibacterial effects of three extracts were determined by agar well diffusion method in ۱۰۰, ۴۰۰ and ۸۰۰ mg/ml concentrations on plant pathogenic bacteria including Xantomonas campestris PTCC۱۴۷۳, Pseudomonas aeruginosa PTCC۱۱۸۱, Pseudomonas syringae PTCC۱۲۹۰, Enterobacter aerogenes PTCC۱۲۲۱, Clavibacter michiganensis PTCC۱۳۹۹, Ralstonia solanacearum PTCC۱۶۰۰ and Gluconacetobacter PTCC۱۷۳۴. 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 N. plumbaginifolia in the minimum concentration (MIC) of ۴۰۰ mg/ml were effective on the most of studied bacteria and had the most effect on P. aeruginosa PTCC۱۱۸۱ with the growth inhibition zone of ۲۲.۵۱ mm (water extract), ۱۹.۳۹ mm (ethanol extract) and ۲۰.۹۴ mm (methanol extract). The concentration of ۸۰۰ mg/ml of the extracts was detected as minimum bactericidal concentration (MBC). The results showed that the methanol extract of N. 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 N. plumbaginifolia leaves had the greatest impact on P. aeruginosa PTCC۱۱۸۱ 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.