‘Hamlin’ oranges were degreened for 1, 2, or 4 days in ethylene concn of 0 to 50 ppm and at 21, 24, 27, and 30°C. The initial rate of chlorophyll loss was more rapid at 30°C than at 21°C. Subsequent changes at 21°C were such that the fruit reached an acceptable color almost as rapidly as at 30°C. After 4 days’ degreening, fruit at both temp showed the same response pattern to the range of ethylene concn used, with the optimum response attained with ethylene concn between 5 and 10 ppm. After short degreening periods, changes continued after removal from the ethylene atmosphere. Responses at 24 and 27°C were similar to those at 21 and 30°C, respectively. No evidence of a seasonal change in the response to ethylene was shown. Stem-end decay generally was greater with increasing ethylene concn, temp, and length of the degreening period. Interactions among these variables were such that increasing the temp or length of degreening period resulted in greater increases in decay at high rather than at low ethylene levels.
The responses of ‘Hamlin’ oranges to varying levels of oxygen and ethylene were studied in a series of tests during the fall of 1967. Increasing ethylene levels up to 5 to 10 ppm resulted in rapid losses of chlorophyll. With 2 days’ degreening, the optimum ethylene level appeared to be higher than during a 1-day period. High oxygen (50%) alone increased the rate of degreening, but high oxygen plus ethylene did not produce any additive degreening response over ethylene alone. Low oxygen (10%) reduced the degreening response to ethylene in both ‘Hamlin’ and ‘Washington’ Navel oranges. In a test on ‘Dancy’ tangerines, the rate of degreening was slower at 70° than at 85°F. Degreening frequently continued after removal from the degreening atmospheres, resulting in modification or elimination of original treatment differences.