Development of a decontamination method to inactivate Acidovorax citrulli on Cucurbitaceae seeds without loss of seed viability

BACKGROUND: Acidovorax citrulli is a plant pathogen causing bacterial fruit blotch in Cucurbitaceae family. Applying high concentration of disinfectants to seeds containing plant pathogen may substantially decrease the germination rate of seeds. Therefore, it is necessary to develop a hurdle technology which can inactivate plant pathogens without decreasing seed viability. This study was conducted to develop a decontamination method to inactivate the plant pathogen Acidovorax citrulli on Cucurbitaceae seeds by sequential treatments with aqueous chlorine dioxide (ClO₂), drying, and dry heat. RESULTS: The maximum ClO₂ concentration that did not lower germination rates of cucumber, honeydew melon, and watermelon seeds was ca. 100 μg mL⁻¹ of ClO₂ for 5 min. Optimal incubation conditions for drying seeds that had been treated with aqueous ClO₂ were determined as 25 °C and 43% relative humidity (RH) for 48 h. The maximum dry-heat temperature that did not reduce germination rates of seeds, which had been treated with ClO₂ and dried at 25 °C, was 60 °C at 43% RH for 24 h. When seeds containing A. citrulli (6.4–7.0 log CFU g⁻¹) were treated with aqueous ClO₂ (50 μg mL⁻¹, 5 min), dried (25 °C, 43% RH, 24 h), and dry heated (60 °C, 43% RH, 24 h), the pathogen was inactivated to below the detection limit from all three seed types (<−0.5 log CFU g⁻¹). CONCLUSION: The decontamination conditions to inactivate A. citrullii from Cucurbitaceae seeds without decreasing the seed viability were determined (sequential treatment with ClO₂ [50 μg mL⁻¹, 5 min], dried [25 °C, 43% RH, 24 h], and dry heated [60 °C, 43% RH, 24 h]). The results of this study may also be applicable to other plant pathogens on other types of seeds.