Seasonal susceptibility of Tarocco oranges to chilling injury as affected by hot water and thiabendazole postharvest dip treatments

Susceptibility of Tarocco (blood) oranges (Citrus sinensis Linn. Obsek) to chilling injury (CI) was investigated with fruit harvested from December through April. The fruit was subjected to a 3 min dip in water with and without thiabendazole (TBZ) at 200 ppm (50 degrees C) or 1200 ppm (19 degrees C, room temperature) and then stored at 3 degrees C and 90-95% relative humidity (RH) for 6 weeks followed by 1 additional week at 20 degrees C and approximately 80% RH to simulate a marketing period(SMP). CI development was significantly affected by the age of the fruit, decreasing later in the season. Water dips at 50 degrees C reduced CI. However, dip efficacy was significantly influenced by picking date and storage duration. Treatments with 1200 ppm TBZ at 19 degrees C also ameliorated CI but had no better effect than water at 50 degrees C. Treatments with 200 ppm TBZ at 50 degrees C significantly suppressed CI development on fruits harvested throughout the season. TBZ accumulation on fruits following 200 ppm dips at 50 degrees C was not significantly dependent on fruit age, while 1200 ppm TBZ at room temperature resulted in significantly higher TBZ uptake in fruits harvested late (April) rather than early (December), with intermediate concentrations of fungicide in fruits harvested from January through March. Residue concentrations in fruits after treatment with 200 ppm TBZ at 50 degrees C were not significantly different from those found following 1200 ppm TBZ dipping at 19 degrees C throughout the season. We concluded that postharvest treatments with 1200 ppm TBZ at room temperature or 200 ppm TBZ at 50 degrees C produced similar TBZ uptake in Tarocco oranges, but TBZ treatments at 50 degrees C water gave the most effective reduction of CI symptoms.