In vitro and in vivo inhibitory effects of gaseous chlorine dioxide against Diaporthe batatas isolated from stored Sweetpotato

Chlorine dioxide (ClO₂) can be used as an alternative disinfectant for controlling fungal contamination during postharvest storage. In this study, we tested the in vitro and in vivo inhibitory effects of gaseous ClO₂ against Diaporthe batatas SP-d1, the causal agent of sweetpotato dry rot. In in vitro tests, spore suspensions of SP-d1 spread on acidified potato dextrose agar were treated with various ClO₂ concentrations (1-20 ppm) for 0-60 min. Fungal growth was significantly inhibited at 1 ppm of ClO₂ treatment for 30 min, and completely inhibited at 20 ppm. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by ClO₂ treatment with different concentrations and durations. Lesion diameters were not significantly different between the tested ClO₂ concentrations; however, lesion diameters significantly decreased upon increasing the exposure time. Similarly, fungal populations decreased at the tested ClO₂ concentrations over time. However, the sliced tissue itself hardened after 60-min ClO₂ treatments, especially at 20 ppm of ClO₂. When sweetpotato roots were dip-inoculated in spore suspensions for 10 min prior to treatment with 20 and 40 ppm of ClO₂ for 0-60 min, fungal populations decreased with increasing ClO₂ concentrations. Taken together, these results showed that gaseous ClO₂ could significantly inhibit D. batatas growth and dry rot development in sweetpotato. Overall, gaseous ClO₂ could be used to control this fungal disease during the postharvest storage of sweetpotato.