Carbohydrates and leaf blackening of Protea cut flowers

[摘要] ENGLISH ABSTRACT: Protea cut flowers are exported worldwide but the vase life of some species and cultivarsis considerably shortened by post-harvest leaf blackening. Research has establishedcarbohydrate depletion to be positively correlated with this disorder. Consequently, astudy had been made of the carbohydrate status of various species and cultivars, as wellas the effect of supplemental glucose (pre and post-storage) on leaf blackening.Glucose, fructose, sucrose and starch concentrations of various Protea species andcultivars held in water were measured at harvest, and again at leaf blackening initiation.All measured carbohydrates declined significantly in 'Carnival', 'Pink Ice' and 'Sheila'.In 'Cardinal' all carbohydrate concentrations decreased significantly, except the sucroseconcentration in the inflorescence. 'Susara' and 'Ivy' had very high initial carbohydrateconcentrations in the leaves which decreased significantly. The very high initialcarbohydrate concentrations in the inflorescence of 'Ivy' declined significantly. 'Brenda'differed from the other cultivars and species in that glucose concentrations increased overtime. Carbohydrate concentrations of most of the tested proteas declined significantlyfrom harvest to the initiation of leaf blackening. This highlighted the dependence of theleaves and inflorescence on the carbohydrate reserves, further substantiating thecarbohydrate depletion theory. The inflorescences were characterized by high fructoseand glucose concentrations and low sucrose concentrations when compared to the leaves. It was hypothesized that glucose pulsing and cold storage at 1°C for three weeks wouldsignificantly reduce leaf blackening. 'Brenda', 'Cardinal', 'Carnival', 'Pink Ice','Susara ' and 'Sylvia' had significantly less leaf blackening with glucose treatments of 4and 10%. Leaf blackening of 'Sheila', P. cynaroides and P. grandiceps was notsignificantly reduced by glucose pulsing. P. magnifica showed a small, but significant,reduction in leaf blackening in response to the 3, 6 and 9% treatments after 10 days only,but despite this, leaf blackening was unacceptably high. 'Pink Ice' harvested at the softtip stage had less leaf blackening than those harvested open or closed. Toxicitysymptoms on the leaves, and in some instances flowers, were observed at higher glucoseconcentrations (8 and 10%) onP. grandiceps, P. cynaroides, 'Cardinal' and 'Sheila'. Allglucose treatments resulted in toxicity symptoms on P. magnifica. A decrease in nonstructuralcarbohydrates post-harvest apparently occurs in all proteas but it appears thatonly members of the Ligulatae respond to glucose.Glucose pulsing followed by cold storage at 1°C for three weeks in combination withpost-storage glucose vase solutions, significantly reduced leaf blackening of some Proteacultivars. Glucose (1 and 2%), with hypochlorite, significantly delayed leaf blackeningin 'Cardinal' and 'Sylvia' after seven days. Leaf blackening of 'Brenda', 'Carnival','Pink Ice' and 'Susara' was not significantly reduced by the glucose vase solutions.Other disinfectants, in combination with the sugar treatments, need to be evaluated sincethe hypochlorite treatment had a dehydrating effect on all the cultivars and resulted inincreased leaf blackening. Carbohydrate supplementation of protea flowers with glucose, pre and post-storage, willhelp meet the post-harvest carbohydrate requirements of certain Protea cultivars andspecies to an extent. Glucose treatments must be seen in conjunction with maintainingthe cold chain and when combined with cold chain maintenance, can extend the storageand vase life.

[发布机构] Stellenbosch University