Chilling injury and the control thereof in selected Leucadendron species

The aim of this study was to gain better understanding of pre- and post-harvest factors that contribute to maintenance of high product quality in Leucadendron cut flower stems during long-term cold storage conditions, as required for export, and to provide valuable information to the Cape Flora SA industry. The objectives of this study were to simulate long-term storage of a range of Leucadendron cultivars and determine the optimum storage regime; to establish and characterise different harvest maturity categories for Leucadendron and to evaluate the effect of different harvesting maturities on the development of chilling injury of Leucadendron.

1) A study was done to establish and provide insight into effective storage protocols for Leucadendron stems and to obtain a better understanding of the development of chilling injury for this niche product with long-term cold storage. Five Leucadendron cultivars were stored for a period 21, 28 and 35 days at 0°C, 2.5°C and 5°C, respectively, and then evaluated for vase life quality using a hedonic index. 2) The susceptibility of stems with four different harvest maturities (M1-M4) to chilling injury was studied in L. ’Chameleon’. Stems were stored at 0°C, 2°C, 4°C, and 6°C respectively, for 21 days. Data collection included scores for visual quality over a 14-day vase life period, and quantification of selected stem characteristics aimed to characterise stem maturity. These included information on flower head fresh weight, flower head size, and internode length. Cold-induced physiological stress was determined using chlorophyll fluorescence and electrolyte leakage. 3)

1) As an exception, L. ‘Blush’ was stored for 14 days as well. Results were inconclusive and could not support a general recommendation for a single optimum storage temperature and duration across a range of Leucadendron products. L. ‘Blush’ was regarded as unsuitable for long-term cold storage, whereas L. ‘Safari Sunset’ performed well over all temperature ranges and storage periods. L. ’Chameleon’ performed well at 5°C while L. ‘Laurel Yellow’ stem quality displayed a significant decrease in quality when stored at 2.5°C, suggesting this temperature as a possible killing zone. L. ‘Inca Gold’ stems stored well at 0°C, across all storage durations. 2) Results indicate harvest maturity has a significant impact on the development of chilling injury. Stems harvested at M1 were negatively impacted by all storage temperatures, whereas stems from M4 remained relatively unaffected by the storage temperatures, yielding marketable stems. This study should be extended to a wider range of Leucadendron cultivars across the harvesting season and in different production regions. Characterization of the various harvest maturities was not achieved. Fluorescence as a rapid and non-destructive indicator for chilling injury showed promise, whereas the use of electrolyte leakage should be further explored for its application in post-harvest detection of chilling injury in Leucadendron.

The first objective determined optimal storage temperatures and durations for exported Leucadendron cultivars with varied colors. L. ‘Blush’ stored poorly (under 14 days), making it unsuitable for sea freight. L. ‘Safari Sunset’ stored excellently for 21-35 days across all temperatures. L. ‘Chameleon’ showed chilling injury at low temperatures after 7 days vase life. L. ‘Laurel Yellow’ had quality drop only at 2.5°C, suggesting a ‘killing zone’. Results were inconclusive overall, with 5°C working for most except L. ‘Inca Gold’. Storage success varied by cultivar.

not provided.

not provided.