Articles
EFFECTS OF GROWTH SUBSTANCES, ETHYLENE INHIBITORS AND HEAT DISINFESTATION TREATMENTS ON CITRUS FRUIT STEM END ROT
To accentuate the potential effects of these compounds, the fruit were challenged with a low concentration of propylene, an active analogue of ethylene.
Using propylene in this way enables endogenous ethylene production by the fruit to be measured.
The fruit used in this investigation were subjected to shrink wrapping in polyethylene film, curing at 36°C for 3 days and heat disinfestation at 45°C for 42 min.
The effect of the removal of the calyces on stem end rot was also examined.
For WNO, application of STS and DNP severely injured the peel and accelerated both browning of calyces and incidence of stem end rot.
Application of spermine, NaN3 and propyl gallate decreased the rates of CO2 production, ethylene evolution and, as a result, retarded the browning of the calyces and incidence of stem end rot.
Ethylene production in control fruit and after STS and 2,4-D acid treatments was higher than in other treatments during storage.
There was no clear response to 2,4-D in this experiment.
A high correlation between stem end rot and browning of the calyces (r = 0.91–0.99) was observed in the various treatments.
For ‘Valencia’ oranges, the application of 250 μg/mL 2,4-D (amine form) greatly retarded the development of peel colour, maintained the fruit in a juvenile condition and reduced the incidence of both brown calyces (buttons) and stem end rot during 35 or 77 days of storage.
The results confirm an earlier view that 2,4-D prevents stem end rot by retarding senescence of the peel rather than by preventing the senescence of the calyces.
Thus the browning of the calyces provides an index of peel senescence.
The application of 10–15 μL/L propylene increased the browning of calyces in ‘Valencia’ oranges that had not been treated with 2,4-D. There were no clear responses to the other chemical compounds.