Ethephon for Postharvest Degreening of Oranges and Grapefruit1

Abstract

Ethephon [Ethrel, (2-chloroethyl) phosphonic acid, 2-CEPA] was tested on ‘Hamlin’ oranges in 2 seasons and on ‘Valencia’ oranges and ‘Marsh’ grapefruit in 1. In 1 picking, very green oranges, mature enough to degreen with gaseous ethylene (C2H4), failed to degreen with ethephon. Once mature enough to respond to ethephon, rate of chlorophyll disappearance was comparable to C2H4 degreening. Waxing sharply arrested color change due to C2H4 degreening, but had comparatively little effect on ethephon-dipped fruit. Stem feeding was effective but impractical. Little correlation was found between degreening rate and: ethephon concn (from 1,000 to 12,000 ppm); immersion time (from 1 to 10 min); or use of vacuum vs. atmospheric pressure during immersion. Duration of color change was sometimes sharply curtailed after brief immersion periods or low ethephon concn. Internal C2H4 levels increased from 0 prior to ethephon treatment to 5-16 ppm 24 hr after, with emanation rates from the fruit of 1 to 6 µl/Kg/hr. It is theorized that a threshold concn is necessary for degreening with no indication of stimulation of autogenous C2H4 production.

Degreening Citrus Fruit with Postharvest Applications of (2-Chloroethyl)phosphonic Acid (Ethephon)1

“…No inhibition was observed at ethephon concn up to 8,000 ppm in 2 tests in 1971 (data not shown). These high concn did not show the extended degreening that has been reported in 'Hamlin' orange (4).…”

“…Preharvest applications of ethephon have shown promise for inducing degreening in some cultivars (1,12,14). Postharvest applications also have shown promise (2,3,4), and such applications avoid the problem of leaf abscission which may occur with applications on the tree. Postharvest applications may be of use as an alternative to ethylene degreening or, as with lemons, to the long holding period required to color non-ethylened citrus fruit, and may be developed into procedures for degreening fruit in-transit.…”

Citrus Physiological Disorders and Their Ameliorating Control Measures: A Review

“…Whole citrus plants have been severely damaged by freezes, and frozen fruits have deformed intercarpellary membranes with visible white hesperidin crystals in between segments. At the stem end, where moisture loss has occurred due to damaged membranes, and form the desiccated areas [36]. Depending on the degree of damage, different countries have different policies regarding the acceptance of frozen fruit.…”