Cellulase Activity, Endogenous Abscisic Acid, and Ethylene in Four Citrus Cultivars during Maturation

At maturity, the fruit of two early maturing orange cultivars, Hamlin and Pineapple (Citrus sinensis [L.] Osbeck), contained more ethylene and abscisic acid than the late maturing Valencia and Lamb Summer (C. sinensis [L.] Osbeck) cultivars. Ethylene (up to 95 nl/l in internal atmosphere) and abscisic (50 mug/kg dry weight flavedo) increased most rapidly in Pineapple, leading to increased cellulase activity and loosening of the fruit. Fruit of the two late maturing cultivars contained less than 25 nl/1 ethylene and 40 mug abscisic acid/kg dry weight of flavedo at peak maturity. Cellulase activity and loosening of the fruit of these late maturing cultivars was slight.