Tomato Seed Disinfection with Chlorine

Chlorine is a commonly used disinfectant for tomato seed contaminated with the bacterial pathogens causing canker, spot, and speck diseases. Previous research has attempted to determine chlorine effectiveness by testing for the presence of the pathogen after treatment of infected seed lots. Even with the most advanced techniques, the accuracy of these methods is questionable, and can underestimate the potential for causing disease. In contrast, this research tested the effectiveness of chlorine for disinfecting tomato seed by plating treated seed onto potato dextrose agar to determine the percentage of disinfected seeds. The elimination of all bacterial growth from seed including bacteria such as Bacillus with highly resistant spores should indicate the efficacy of a treatment for the elimination of bacterial pathogens. Dry seed that was previously extracted by fermentation could be effectively disinfected after pre-soaking in water for 24 hours at a temperature inhibitory to germination, and then treating with 5000 mg/L chlorine at 20°C at pH 9.5 for 60 minutes with constant agitation. The threshold level for disinfection was 2500 mg/L of chlorine resulting in less than 1% infested seeds, but slightly more than 0%. Oxidation of the seed coat by the hypochlorite ion was the main factor resulting in disinfection, but an additional effect from the presence of low levels of hypochlorous acid was also found.