Leaf blackening in Protea neriifolia R. Br. is influenced by sink demand and nectar production. Maximum nectar production occurred when the flower was in the cylindrical shape. C14-sucrose applied to a postharvest flower stem leaf moved preferentially into the nectar (65%). Darkness increased the rate of leaf blackening. Covering an individual leaf on a postharvest flower stem with aluminum foil lead to leaf blackening in 3 days while removing the inflorescence or girdling the stem just below the inflorescence prevented this leaf blackening. Girdling the stem around a leaf base and covering this leaf with foil resulted in leaf blackening in 5 days, but removal of the inflorescence influence did not prevent blackening. Sucrose 2.5% (w/v) in the vase solution prevented leaf blackening in both girdled and non-girdled leaves covered with foil. Polyphenol oxidase apparently plays an important role in protea leaf blackening. Leucospermum, another genera in the family of Proteaceae, did not show any PPO activity and did not blacken in the dark, while high PPO activity was detected in leaf extract of P. neriifolia.
Members of the genera Protea , Leucospermum R. Br., and Leucadendron R. Br. are predominantly grown in South Africa for export to Europe. Manipulation of flowering time in these cut flowers is important in taking advantage of high-spring to
Abstract
“Is it real?” is the usual question. Yes, pincushion protea, Leucospermum cordifolium (Salisb. ex Knight) Fourcade is the first of the ornamental proteas to be grown in quantity as a cut flower in the United States.
The influence of storage temperature and humidity on pollen viability was studied in four Protea species. Pollen was stored at a range of temperatures and relative humidities for up to 1 year and tested for ability to germinate in vitro. Pollen of P. repens (L.) L. `Sneyd', P. eximia (Salisb. ex Knight) Fourcade `Fiery Duchess' and P. magnifica Link. clone T 84 07 05 stored at -196 °C and -14 to -18 °C retained a germination percentage as high as that of fresh pollen regardless of humidity. Humidity control became increasingly important at storage temperatures above 0 °C. The study showed that long-term storage of Protea pollen is not feasible at temperatures above 0 °C. The relationship between germinability and fluorochromasia (FCR) was studied during storage of `Sneyd' pollen. The correlations between FCR and germinability were found to be low and nonsignificant. Fifteen-month-old cryopreserved `Sneyd' pollen functioned in fertilization and seed set as effectively as fresh pollen.
Glucose, fructose, sucrose, and starch concentrations were determined in leaves and inflorescences of protea cutflower cultivars soon after harvest and at the onset of leaf blackening while standing in water. At the onset of leaf blackening sugars and starch were lower in both inflorescences and leaves. Proportionately, sugars and starch decreased more in leaves than in inflorescences. Flower-bearing shoots of `Sylvia' were pulsed individually with 5% glucose solution until each shoot had taken up 10 mL solution. Water served for control treatment. Flowers were then stored for 21 days at 1 °C. After pulsing and after cold storage groups of flowering shoots were separated into inflorescence, leaf and stem components and glucose and starch content determined. Glucose content, determined upon completion of pulsing treatments, was significantly greater in all shoot components of shoots pulsed glucose compared with nonpulsed control shoots. Glucose content of leaves was significantly greater after storage for shoots pulsed than control shoots. Starch content of leaves determined upon completion of pulsing treatments was significantly greater in shoots pulsed with glucose than that of controls. There was a significant decrease in starch content for all tissue types during 21 days of storage. Pulsing flower stems of seven protea cultivars before 3 weeks cold storage significantly reduced the incidence of leaf blackening when assessed both on day 1, and again on day 7 after 3 weeks of cold storage. Supplementing holding solutions with 1% or 2% glucose reduced leaf blackening of proteas pulsed with glucose and cold stored for 3 weeks.
rainfall and an increase in the magnitude and frequency of flood events ( Midgley et al., 2016 ). The potential impact of increasing temperatures due to climate change on cultivated Protea inflorescence production is unknown. A study by Louw et al. (2015
Leaf blackening of Protea neriifolia is a common postharvest problem which renders flowers unsalable. Previous reports suggest that depletion of carbohydrates in source leaves caused by transfer of carbohydrates to the strong flower sink may be a major cause. Flowering stems of P. neriifolia were harvested in California under standard conditions and shipped to Baton Rouge, La. Upon arrival, the stems were re-cut (1 cm.), the number of leaves counted and the diameter and height of the flowers measured. Stems were transferred to 1 liter deionized distilled water containing 50 ppm hypochlorite, and 0.5% sucrose or no sucrose, and placed in a growth chamber (25°C) either with 12 hrs light (120 μmol/m2/s), or 24 hrs darkness. Number of leaves 10% black, flower diameter and height, and carbon exchange rates were measured every two days over a 16 day interval. Soluble and insoluble nonstructural carbohydrates were determined and assimilate export rate was estimated for each sampling day. Stems placed in the light maintained healthy foliage while those in the dark had 77-l00% of their leaves 10% black by day 8. Flower and leaf quality in the fight treatment were superior with addition of sucrose to the vase solution. Influence of treatments on carbohydrate metabolism in relation to leaf blackening and flower development will be discussed.
Protea cynaroides L., known as King Protea, is a well-known cut flower in the international floriculture industry. The most characteristic feature is its attractive flowerhead, which typically consists of hundreds of flowers. In vitro propagation
The strategy of this study was to determine the period of floral initiation for both species and then to determine the critical regulator(s) of flower initiation and floral development. Plants grown under different temperature regimes gave best shoot extension and flower initiation at temperatures with 10°C night and 15 to 25°C day. Field data from four locations showed a correlation of time of flower initiation and temperatures over the same range.
Temperature is an important determinant of the vegetative flush period of both species. The stem diameter of all shoots is a consequence of the vegetative flush growth and in turn is well correlated with flower initiation. Plants given day temperatures of 20°C or above remain in the vegetative phase. Flower abortions in Protea neriifolia and reversions from floral to vegetative shoots in Protea cynaroidesresult from high day temperatures.
Daylength was not found to be critical for flower initiation. A cool temperature period acts as a control to change shoots from the vegetative to reproductive phase.
The King Protea ( P. cynaroides L.) is a semihardwood shrub that produces striking flowerheads consisting of hundreds of florets. It is an important cutflower in the floriculture industry. Because of its slow-growing nature and susceptibility to