Reactions of Some Tomato Cultivars against Pseudomonas syringae Pv. Tomato

Pseudomonas syringae pv. tomato is the causative agent of the bacterial speck disease of tomato (Solanum lycopersicum), a disease that occurs worldwide and causes severe reduction in fruit yield and quality. Disease resistance conferred by the pto gene, encodes a serine–threonine protein kinase, is one of the first R-genes to be cloned and sequenced. In this research, the resistance reactions of 44 popular tomato cultivars which are grown commonly in Turkey against P. s. pv. tomato causal agent of bacterial speck disease were determined. Six-week-old plants were inoculated by spraying of P. s. pv. tomato YA-1 and YA-2 strains (10⁸ cfu·ml^-1) with an airbrush until leaf surfaces were uniformly wet. After inoculation, the plants were incubated at 25 ± 1 °C in 60% to 70 % relative humidity with a 12-h photoperiod and the disease progress occurred on the seedling leaves by P. s. pv. tomato was followed by counting the dark brown-black leaf necroses in 2 days after inoculation of the seedlings. Each experiment was performed at least three times and control plants were sprayed with sterile distilled water. The results of resistance reactions on plants were evaluated according to Chambers and Merriman scale. The total peroxidase activity (U/ml) was measured by a spectrophotometric method at λ=460 nm using H₂O₂ as a substrate in 24, 36, and 72 hours after bacterial inoculations. The resistance levels of the cultivars were statistically determined by using ANOVA variance analyze and Duncan multiple range tests. Presence of pto gene (963 bp) in the tomato cultivars was verified by using the primers SSP17 and JCP32 by PCR and the gene was determined in 15 different tomato cultivars.