Unravelling and manipulating the physiological processes associated with leaf blackening in Protea cut flower stems for enhanced and extended product quality to meet market demands

Protea cut flowers are popular internationally but suffer from leaf blackening, a postharvest disorder causing consignment rejection. To avoid this, stems are often exported leafless, losing the foliage’s nutritional support. The shift from air to sea freight exposes stems to longer transport, worsening issues like chilling injury and leaf blackening. Solutions require innovative postharvest treatments based on physiological understanding, prioritizing cooling to reduce respiration. Research into leaf blackening genetics could enable future resistant cultivars, helping South Africa maintain and expand its market share.  Objectives included 1)  To evaluate the use of DCA technology and ILOS for the control of blackening in Protea; 2)  To evaluate the use of an ethanol enzymatic assay for the determination of low levels of internal ethanol which can be effective in inactivating enzymes and/or phenolic reaction that may be causal to leaf blackening; and 3) To characterize the phytochemical profiel of Protea species and hybrid cultivars with the aid of liquid chromatography-ion mobility mass spectrometry with the aim to isolate and study specific metabolites that may serve as a marker for leaf blackening.

Three Protea cultivars (‘Sylvia’, ‘Pink ice’, ‘Carnival’) were sourced and prepared by standardizing stem length to 50 cm. The experiment followed a complete randomized block design with two main groups: stored and fresh (non-stored). Stored treatments included three modified atmosphere packaging (MAP) types (Xtend®, Chrysal FreshLiner, Chrysal FreshPaq) and an unbagged control, stored for 18 days at 1°C to simulate sea freight. Fresh treatments included non-pulsed and pulsed (6% glucose) controls. After storage or pulsing, stems were evaluated in vases for leaf blackening percentage and inflorescence quality (0-5 scale) over 10-12 days. Statistical analysis used ANOVA with repeated measures and Fisher’s LSD test (P<0.05).

The results indicated that Floralife products before significantly better than the control (no treatment), but also performed better than what the industry is using currently, or than the solutions formulated by the competitor Chrysal. Further evaluations on a wider range of products, throughout the year, is thus suggested to confirm this finding. This finding is however supported in recent trial done in our laboratory, where Floralife outperformed Chrysal in numerous rose cultivars, and over three trials.

For the MAP study, the general conclusion were that MAP technologies hold limited potential, for use as a post-harvest treatment, to extend the marketable shelf life for ‘Sylvia’, ‘Pink ice’ and ‘Carnival’ cut flowers when used in isolation. The efficacy of MAP treatments is highly dependent on the cultivar-treatment combination tested and the quality parameter used for evaluation. The vase life of ‘Sylvia’ is so short that MAP treatments may be uneconomical, therefore it is recommended that ‘Sylvia stems should be sold a fresh. The onset of leaf blackening for ‘Sylvia’ and ‘Carnival’ during storage was high, rendering the use of the tested MAP treatments unfeasible in these cultivars.Chrysal FreshPaq may be a viable MAP treatment for ‘Pink ice’ to reduce leaf blackening, however this treatment lowers inflorescence quality.The efficacy of MAP treatment for both mixed flower shipments and single cultivar shipments needs to be further tested on a wider variety of cultivars. Further economic studies are needed to determine the economic feasibility of MAP flower treatments on Protea, given its high cost. Further studies are needed to determine the feasibility of MAP when used in combination with other postharvest techniques on Protea.

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