Determination of optimal sulfur dioxide time and concentration product for postharvest control of gray mold of blueberry fruit

Highbush blueberries (Vaccinum spp.) are a major export fruit crop of Chile which is stored at 0 °C and transported to markets in Asia, Europe, and the USA, using more than 15 d of maritime transportation. Under these conditions, gray mold caused by Botrytis cinerea can produce important economic losses. The effectiveness of sulfur dioxide (SO2) concentration × time treatments on gray mold control was determined in the laboratory and validated prior to refrigerating the fruit, using pallet scale SO2 fumigation treatment on the following blueberry cultivars: 'Brigitta', 'Legacy', 'Liberty' and 'O'Neal'. In inoculated 'Brigitta' and 'Liberty' blueberries, gray mold prevalence varied from 97.2% to 97.5% in non-treated fruit, and this value was reduced from 7.9% to 6.1% in blueberries that were exposed to a SO2 concentration × time (Ct) product of 400 (μL L−1) h. The relationship between SO2 Ct products and gray mold prevalence under laboratory conditions was best explained by exponential models, which had a determination coefficient (R2) that ranged from 0.88 to 0.96. The estimated EC90 values varied between 245 and 400 (μL L−1) h, and the SO2 Ct between 250 and 350 (μL L−1) h was validated using a pallet scale application treatment to obtain the best control and minimal variation. No visual phytotoxicity symptoms of SO2 were observed with the Ct that was tested in this study. Therefore, SO2 fumigation was demonstrated to be an effective and practical technology for reducing the risk of blueberry gray mold decay during storage, and further effort should be given to register the use of this product for blueberries in the main Chilean export markets.