Ethanol vapour reduces leaf blackening in cut flower Protea 'Pink Ice' stems

The effect of ethanol vapour on postharvest leaf blackening of Protea susannae X compacta 'Pink Ice' stems stored in plastic bags under darkness at 20 degrees C (+/- 1 degrees C) was assessed over a 19 day period. Application of ethanol vapour to the stems significantly reduced leaf blackening. Stems exposed to 5.6 g ethanol kg(-1) stem weight, had the least amount of leaf blackening with less than 20% of leaves blackened by day 14. In contrast, the control stems had 50% of leaves blackened by day 9, and 100% by day 15. The highest ethanol treatment at 11.2 g ethanol kg(-1) stem weight caused substantial blackening within the first 24 h of the treatment being applied. Ethanol vapour concentrations in the bag head space decreased rapidly in comparison with the bags with no stems, suggesting that ethanol was rapidly taken up by the stems. Only the highest ethanol treatment had detectable levels of ethanol in the bags after 17 days, and ethanol vapour had no effect on CO2 concentration in the bag head space. Carbon dioxide concentrations ranged between 1.0 and 2.5%. The rate of leaf blackening on the bagged stems without ethanol was significantly less than on stems not in bags, suggesting that elevated CO2 levels may have contributed to reduced blackening. (C) 1999 Elsevier Science B.V. All rights reserved.