EFFECT OF ETHANOL VAPOUR ON LEAF BLACKENING OF SELECTED PROTEA SPECIES

Abstract

Postharvest leaf blackening is a significant limitation to the commercial viability of several Protea cut flower products particularly those undergoing prolonged low temperature storage. Although postharvest carbohydrate supplementation is successfully used to reduce leaf blackening in susceptible Protea cut flowers the problem persists for prolonged storage. The finding that ethanol vapour exerted some control of leaf blackening in Protea 'Pink Ice' stored at 20°C led to the current study to determine whether ethanol vapour could further reduce leaf blackening in 'Pink Ice' (P. susannae × P. compacta), 'Syliva' (P. eximia × P. susannae) and P. magnifica cut flowers under prolonged cold storage (4±1°C). Stems of 'Pink Ice' and 'Sylvia' (pre-pulsed with 10% glucose solution) were exposed to concentrations of 0, 1.5, 2.5, 3.5, 4.5 and 5.5 g ethanol kg fresh weight -1 . Except for the 5.5 g ethanol·kg fresh weight -1 treatment Protea magnifica stems received the same ethanol treatments. 'Pink Ice' was stored for two, three and four weeks, whereas 'Sylvia' and P. magnifica were stored for only three weeks. Upon termination of 15 day vase life assessment, leaf blackening of 'Pink Ice' was lowest (40%) on stems stored for two weeks subjected to 2.5 g ethanol·kg fresh weight - compared to 90% leaf blackening in untreated controls. However, at longer storage periods this beneficial effect on suppressing leaf blackening was not retained. Leaf blackening of 'Sylvia' and P. magnifica was not significantly suppressed by any ethanol treatment.