ClO₂ dipping treatment inhibits gray mold on cut rose flowers during storage

This study investigated the antifungal effect of chlorine dioxide (ClO₂) dipping on Botrytis cinerea, the causal agent of gray mold, on cut rose flowers (Rosa hybrida L.). In vitro, the spore germination of gray mold was inhibited 100% by instant dipping with ClO₂ solution (5 to 10 μL·L⁻¹). In particular, ClO₂ at 5 μL·L⁻¹ was found to be ideal for hindering spore activity without causing any damage to the petals. This ClO₂ antifungal effect on cut flowers was investigated in a white cultivar ‘Beast’ with different treatments: dipping (one second), spraying (4.8 mL), or gassing (two hours) with 5 μL·L⁻¹ ClO₂. Six days after ClO₂ treatment, the incidence of gray mold in the artificially-inoculated flowers was 2.5% (dipping), 9.4% (spraying), or 8.4% (gassing), respectively, which were all significantly lower than the control incidence of 17.6%. Especially, ClO₂ dipping reduced the incidence of gray mold by up to 26.1% compared to the control in five other rose cultivars (‘Antique Curl’, ‘Green Beauty’, ‘Feel Lip’, ‘Pink Heart’, and ‘Venus Berry’). No petal discoloration was detected, and petal color values (chroma or hue) were maintained regardless of ClO₂ dipping. This result suggests that immediate ClO₂ dipping is applicable to inhibit gray mold on cut rose flowers at a level of 5 μL·L⁻¹ just before postharvest storage.