The Daffodil Delay in Iris
Scientists in Germany and The Netherlands have discovered that a daffodil, more specifically the compound narciclasine found in the daffodil stem mucilage, delays the tepal senescence in cut Iris. Iris x hollandica are usually harvested when the tepal tips just emerge above the green sheath leaves. The flowers proceed to open when placed in water at 20°C (68°F). Visible senescence symptoms, including turgor loss, naturally appear within four to five days.
In this experiment the Iris cultivar ‘Blue Magic’ was harvested when about 1 cm of the tepals were visible. Flower opening occurred primarily during the first day and was complete after day two. For observation purposes, senescence symptoms were divided into five stages. Stage 1 was identified by a slight flower discoloration and the beginning of inward rolling at the distal tepal edge. When the entire tepal had lost its purple color and become yellowish white, Stage 5 was observed, immediately followed by desiccation.
A Narcissus pseudonarcissus ‘Carlton’ stem was placed in the vase water with the Iris stems. The daffodil flower considerably delayed or even prevented development of senescence symptoms past stage 1. Eventually, the Iris flowers wilted and desiccated retaining its color. The same effect was observed by placing mucilage from the daffodil stems in the water at concentrations below 0.5 ml/L. At concentrations 1.0 ml/L and higher, toxicity symptoms were observed. The daffodil delay effect was not effective if the daffodil was not placed in the water prior to day 2.
The compound in daffodil stem mucilage and daffodil bulbs was identified as narciclasine. Interestingly, other daffodil cultivars had various effects on the Iris, some equally effective, others ineffective. It may be possible that the various cultivars have different concentrations of mucilage.
van Doorn, W.G., A. Sinz, M.M. Tomassen. 2004. Daffodil flowers delay senescence in cut Iris flowers. Phytochemistry 65 pp. 571-577.
Irradiation of Cut Flowers
The Institute of Nuclear and Energy Research in Brazil considered the phytosanitary inspection of fresh cut flowers for import/export. Methyl bromide treatment is currently the disinfestation method of choice. Though very effective, its eminent ban due to its affect on the environment has prompted the search for an equally effective alternative. Some alternatives include carbonyl sulfide, phosphine and heat treatment. All of these have limitations compared to methyl bromide such as a weaker effectiveness or resultant plant damage. While there may not be a single replacement for methyl bromide, scientists continue to test various alternatives, including radiation treatment.
Thirteen cut flower species were tested with gamma and electron-beam irradiation. The irradiation was carried out in a panoramic cobalt-60 source and in an electron beam accelerator. A dose of 300 Gy was the minimum value a flower had to withstand in order to be considered tolerant of radiation. At 300 Gy, all stages of insects and mites become sterile. After treatment, the flowers were held in a preservative solution at room temperature for quality observation.
The following table indicates each species tolerance level and/or its signs of intolerance. No visible parameters such as plant family, plant structure or flower color were identified as easy indicators of radiation tolerance. At this time, continued species-specific trials will be required to verify a flower’s tolerance to irradiation.
|Radiation (Gy)||Beam (Gy)||High does cause bud opening inhibition|
|Lillium speciosum||Liliaceae||Up to 500||Up to 300||Browning|
|Alpinia purpurata||Zingiberaceae||Up to 400||Up to 300||Browning|
|Curcuma alismatifolia||Zingiberaceae||Up to 500||Not Tolerant||High does cause bud opening inhibition & petal wilting|
|Lisianthus sp.||Gentianaceae||Up to 700||Up to 300||Petal withering|
|Eustoma grandiflorum||Gentianaceae||Up to 400||Not Tolerant||Browning|
|Zingiber spectabile||Zingiberaceae||Not Tolerant||Not Tolerant||Bent stem and curling petals|
|Gerbera sp.||Compositae||Not Tolerant||Up to 300||Browning and drying up|
|Strelitza reginae||Musaceae||Not Tolerant||Not Tolerant||Browning and drying up|
|Heliconia psittacorum||Musaceae||Not Tolerant||Not Tolerant||Browning and drying up|
|Heliconia rostrata||Musaceae||Not Tolerant||Not Tolerant||Petal withering and flower drop|
|Dendrobium phalenopis||Orchidaceae||Not Tolerant||Not Tolerant||Petal withering and flower drop|
|Mattihiola incana||Brassicaceae||Not Tolerant||Not Tolerant||Petal withering and flower drop|
|Bouvardia spp.||Rubiaceae||Petal withering and flower drop|
Kikuchi, O.K. 2003. Gamma and electron-beam irradiation of cut flowers. Radiation Physics and Chemistry 66 pp. 77-79.
A Closer Look at Vacuum Cooling
Moisture loss is recognized as one of the main causes of deterioration in harvested plant products. Even small losses can result in wilting of leaves or petals, while higher losses may result in permanent quality loss. As the temperature is decreased, water loss is reduced; therefore, the rapid cooling of plant products plays a key role in minimizing water loss and preserving harvest quality. While vacuum cooling has been an effective method for pre-cooling of some horticultural crops, there are several issues to address regarding its use on cut flowers. Researchers at the National University of Ireland looked at the cooling rate, mass loss and vase life of vacuum cooled cut lily flowers.
Previous research has shown that spraying water on the product can reduce mass loss by providing additional refrigerant (in addition to the water available in the plant) to allow the cooling process to occur without evaporating plant held water. Of course, excessive water may be detrimental to cut flowers by inducing chilling injury or increasing disease risks.
All flowers (Lilium ‘White Elegance’) were harvested when the first flower was fully colored but not yet open. The stems were placed flat on a perforated stainless-steel table and cooled from harvest temperature to 5°C (41°F) or for a fixed cooling period of 10 minutes in the vacuum cooler. Four pressure reduction rates were evaluated. After treatment, some flowers were placed under simulated storage, while others were placed directly in room conditions for a determination of vase life.
Rate of evacuation was shown to effect mass loss with the slowest evacuation rate (8.5 mbar/min) being the most efficient cooling method. Interestingly, the initial mass of the samples had no influence on the total mass loss during cooling. The greatest temperature reduction occurs in the first 100 seconds of all the cooled samples. During this time period the free surface water is evaporated. Since surface area was similar among the samples, this suggests that the cooling rate is influenced by such factors as water activity, moisture permeability and moisture transfer rate to the surface of the plant.
No difference was observed in the vase life of flowers vacuum cooled with additional water or flowers dry vacuum cooled. The average vase life of the different wet treatments was 9.7 days (stored) and 11.2 days (unstored). Similarly, the dry treatment vase life was 9.6 and 11.4 days.
Brosnan, T., Sun, D. 2003. Influence of modulated vacuum cooling on the cooling rate, mass loss and vase life of cut lily flowers. Biosystems Engineering 86(1) pp. 45-49.