Fruit Removal Force, Cellulase, and Ethylene Production in Release and Ethephon-treated Oranges1

Abstract ‘Hamlin’ and ‘Valencia’ oranges [ Citrus sinensis (L.) Osbeck] were treated by stem uptake or dipping in 5-chloro-3-methyl-4nitro-1H, pyrazole (Release) and (2-chloro-ethyl) phosphonic acid (ethephon) of varying concentrations. Depending upon chemical concentration and fruit maturity, fruit removal force (FRF) was reduced within 24 or 48 hours. More buffer and salt extractable cellulase activity were produced after ethephon than after Release treatment, both exceeding the control. Buffer soluble cellulase activity was treatment concentration dependent while salt released cellulase activity was chemical (Release, ethephon, or control) dependent, increasing by the same amount regardless of treatment concentration. Two ethylene peaks, resulting in an M-shaped curve, occurred after dipping oranges in Release. The peak due to chemical treatment (chemical peak) appeared first and was concentration dependent, being of greater magnitude and earlier in time with the higher concentrations. Measurable ethylene production after stem uptake of the chemicals was erratic and represents an inadequate and erroneous procedure for determining effectiveness of a potential abscission chemical.