Rabbiteye blueberry ‘Powderblue’ plants grown at the Durham Horticulture Farm in Watkinsville, GA were used for ethephon treatments on June 23rd, 2017. Ethephon (250 mg·L− 1) and control treatments were applied following the method described in [75 (link)]. Each treatment had four biological replicates. Phenotypic data collected included ethylene evolution from fruit and the rate of ripening. Ethylene evolution from fruit was measured using a closed system. Approximately 25 g of fruit were harvested from each blueberry plant (biological replicates) two days after treatment and incubated in an air-tight 125 mL glass jar with a lid fitted with a rubber septum, for 4 h at room temperature. Headspace samples (1 mL) were analyzed by GC-17 A gas chromatography (GC-17 A, Shimadzu, Japan) equipped with a 2 m micropacked column (Hayesep N, Restek, PA, United States) and a flame ionization detector. The temperature of the injection port and the detector of the GC were set at 200 oC. The temperature program was 60 oC for 4 min; increased by 20 oC.min− 1 to 150 oC; and held at 150 oC for 1 min. The peak area from the resulting chromatograph and a standard curve generated using various concentrations of ethylene were used to determine ethylene evolution from the fruit sample and expressed as nL·g− 1·h− 1. The rate of ripening was determined by visual color assessment, following the method described in [75 (link)]. In short, 3 branches were tagged on each blueberry plant, included around 100 fruits in total. The color of Green, Pink, and Ripe (blue) fruits on the 3 branches were counted when fruits were still attached to the plant at 0, 1, 2, 3, 5, 7, 10, 14 days after the treatment. Green fruit were classified as mature and appearance of color (~ 25% pink coloration) indicating ripening initiation. Pink fruit displayed predominantly pink with some blue (< 10%) and Ripe as fully blue fruit.
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