Preharvest gibberellic acid (GA) applications at 10 ppm in 0.1% L-77 (v/v) surfactant or 20 ppm in 0.05% L-77 (v/v) caused `Marsh' grapefruit (Citrus paradisi Macf.) to be significantly more resistant to puncture and significantly delayed yellow color development. There was no difference between the two GA rates and applications in July were not found to be as effective as August or September applications. There was an overall significant increase in peel oil content in flavedo tissue as a result of GA treatment, but no significant difference between GA treatments. Limonin contents in GA-treated grapefruit albedo tissue were generally higher at both GA levels than in control fruit. GA treatments had no effect on juice quality characteristics and there was no difference in taste preference between GA-treated and control fruit. Because citrus fruit are resistant to attack by tephritid fruit flies prior to the occurrence of peel senescence and GA delays peel senescence, GA treatment should provide a biorational addition to existing fruit fly control strategies.
Roy E. McDonald and Philip E. Shaw
Robert D. Hagenmaier and Philip E. Shaw
The permeability to O2, CO2, C2H4, and water vapor was determined for 19 commercial fruit wax coatings, four ingredients thereof, and one shrink-wrap film. For the commercial coatings, the O2permeability at 50% relative humidity and 30C ranged from 470 to 22,000 ml (STP) × mil/(m2 × day × atm) (1 mil = 0.0254 mm) with CO)2. permeability two to eight times as high. Permeability to noncondensable gases tended to be higher for coatings made from carnauba wax than for those made from shellac and rosin. Commercial fruit wax had sufficiently low noncondensable gas permeability to account for large reductions in the respiration rate of coated fruit. Wax coatings could be improved if permeability were controlled: