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- Author or Editor: M. F. Oberbacher x
Growth of fungi from the surface of excised peel taken from Florida citrus fruit interfered with controlled studies on pigment changes of the flavedo. Control of these fungi was not achieved even though whole fruits were dipped in various concentrations of sodium hypochlorite before removing discs of peel for incubation in culture on a defined medium (5). Normally, the presence of fungal growth was evident on all discs of excised peel after 3 to 5 days incubation at 30°C. Development of a technique to control these fungi was necessary to allow longer incubation of discs to observe pigment changes.
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.