Effectiveness of Some Plant Extracts to Bacterial Speck Disease on Tomato

Bacterial speck, caused by Pseudomonas syringae pv. tomato, is a serious disease on tomatoes grown during winter and spring in protected environments along the coastal area. P. s. pv. tomato control is mainly related to appropriate cultural practices and preventive cupric treatments. Promising plant extracts for the management of plant diseases are environmentally safe, long-lasting. The aim of this study was to evaluate the effectiveness of plants extracts on tomato plants against P. s. pv. tomato and their effects on plant growth in greenhouse conditions. The extracts obtained from leaves, stems or leaves and stems of walnut (Juglans regia), eucalyptus (Eucalyptus globulus), thyme (Thymus vulgaris), rosemary (Rosmarinus officinalis), sumac (Rhus coriaria), moringa (Moringa oleifera), wild bishop (Bifora radians), hop (Humulus lupulus), corekotu (Nigella sativa), black carrot (Daucus carota), and olive (Olea europaea). Two virulent strain of P. s. pv. tomato used in all experiments. The minimum inhibitory concentration (MIC) values were determined by using modified disc diffusion method at five different concentrations and streptomycin sulphate and sterile distilled water were used as positive and negative controls, respectively. Results obtained show that all the eleven plants tested inhibited the bacterial growth of the pathogen with inhibition zone diameter ranging from 2 to 55 mm. In greenhouse, P. s. pv. tomato strains at 10⁸ CFU/mL concentration were inoculated to leaves of pto resistance gene-free tomato cultivar ‘Rio Grande’ by spraying. Some growth parameters (plant height, fresh and dry matter weight) were determined 30 days later after applications and the disease symptoms were evaluated by 0–5 scale in the experiments. Rhus coriaria and Thymus vulgaris extracts were the most effective against P. s. pv. tomato after streptomycin and they reduced disease severity in 39% and 47% ratios, respectively. As a result of all experiments, applications of some plant extracts suppressed the bacterial disease of tomato and increased growth parameters. This study indicated that some plant extracts may be used in prevention programs to combat the bacterial speck disease on tomatoes.