The vase life of cut flowers is determined by various physiological factors that determine the rate of their senescence. A thorough understanding of these factors is required in order to design treatments that will extend the vase life and delay senescence of cut flowers. Senescence of climacteric flowers such as carnations (Dianthus caryophyllus L. cv. Nordika and cv. Snow White) and freesias (Freesia refracta cv. Athena) is characterized by a climacteric rise in respiration rate and ethylene synthesis during the late stages. The increase in ethylene production is preceded by an increase in the sensitivity of the flowers to ethylene. Pulse treatments with sucrose caused a delay and suppression of the climacteric rise in ethylene synthesis and a delay in the climacteric maximum of the respiration rate. A pulse treatment for 24 hours with a 20% sucrose solution was most effective in extending the longevity of both carnations and freesias. The ability of the receptor molecules to bind ethylene is greatly reduced when flowers are pulse-treated with sucrose. In freesias, the ability to bind ethylene is reduced even further when flowers are treated with STS or 1-MCP. Ethylene synthesis in freesias is suppressed and inhibited when treated with STS or 1-MCP but longevity of the freesias and number of open florets on the stem is not increased. The uptake and distribution of sucrose in the buds of freesias is seen by the distribution of sucrose from the first bud on the stem to the next bud after the bud opens. The distribution of sucrose from one bud to the next results in more buds opening on the stem than that on the stems of STS or 1-MCP treated freesias. It is thus clear from the results of the study, that pulsing senescing climacteric flowers with sucrose increases the vase life of the flowers and suppresses ethylene sensitivity of the flowers, thus delaying the autocatalytic process of ethylene production. It is also evident from the results that the osmolality in the flowers has a direct influence on the metabolic processes of the flowers. In freesias, pulse treatment with sucrose increases the number of open buds on the stem and delays senescence of the florets. / Mr. C.S. Whitehead

Südafrikanische Iridaceae enthalten viele Gattungen mit hohem Potential als neue Zierpflanzen. Von Anfang 2005 bis 2007 fanden Untersuchungen an vier geophytischen Arten aus dem Kapländischen Florenreich statt. Den Gattungen Freesia, Sparaxis und Tritonia angehörend, wachsen diese auf der Südhemisphäre während des Winters heran und blühen im Frühjahr. Bei einer Anzucht im europäischen Herbst bzw. Winter könnten ihre niedrigen Temperaturansprüche für den zukünftigen Produzenten eine energiegünstige alternative Kultur bedeuten. Folgende Untersuchungsziele standen im Mittelpunkt: Export während der Dormanz der Knollen, Lagerbedingungen nach dem Export, Pflanzsätze zu verschiedenen Jahreszeiten in Deutschland und allgemeine Ansprüche an die Wachstumsfaktoren. Die Ergebnisse wurden durch regelmäßige Bonitur der Entwicklung der Knollen bzw. Pflanzen gewonnen. Das Nachvollziehen der Infloreszenzanlage erfolgte durch mikroskopische Untersuchungen des Apikalmeristems während des Wachstums. Der Export der Knollen war unkompliziert und ihre Dormanz konnte durch eine Lagerung bei über 20 °C weiter aufrechterhalten werden. Für eine erfolgreiche Blüte nach der Pflanzung stellte die Temperatur den entscheidenden Faktor dar. Die Arten zeigten sich unterschiedlich empfindlich, doch war eine Kulturtemperatur von 13 °C nachts notwendig, wenn die Temperaturen tags über 17 °C lagen. Während der Sommermonate wurden auf Grund der hohen Temperaturen die Infloreszenzen erst gar nicht angelegt oder abortiert. Die vorherrschenden niedrigen Lichtintensitäten der Wintermonate führten ebenfalls zu einem Infloreszenzabort oder einer verspäteten Anthese. Durch spezielle Lagerbehandlungen der Knollen konnte bei der Anzucht eine Reduzierung der Pflanzenhöhe und eine verbesserte Blühleistung erzielt werden. Zusammenfassend lässt sich ein großes Potential der untersuchten Arten für eine energiegünstige Produktion und eine Erweiterung des Herbst-/Wintersortiments an Topfpflanzen in Europa feststellen. / South African Iridaceae contain many genera with a high potential for new floricultural crops. From the beginning of 2005 until 2007, investigations on four geophytic species native to the Cape Floral Region were conducted. Belonging to the genera Freesia, Sparaxis and Tritonia, they are winter growing/spring flowering in the Southern Hemisphere. If forced as pot plants for the European autumn/winter months, their low temperature requirements during cultivation could represent substantial energy savings for the future grower. The investigations focused on the following aspects: export during the corm dormancy, storage conditions after export, forcing experiments in different seasons in Germany and general cultivation requirements. Results were obtained by regularly monitoring the corms and the plant development. Inflorescence initiation was determined by microscopic examination of the shoot apical meristem during the growing season. - The export of dormant corms was uncomplicated and their dormancy could be further maintained in subsequent storage in Berlin at temperatures above 20°C. Temperature was found to be the main criterion to successfully realise flowering after planting. The species varied in their sensitivity, but generally cultivation at 13°C at night was essential, with temperatures of 17°C and above possible during the day. During the Central European summer months, inflorescences in the terminal bud failed to completely develop or flower primordia were aborted due to the high temperatures present. Furthermore, the naturally low light intensities during the Central European winter months also led to inflorescence abortion or a delay in flowering of three species. A reduction in plant height and enhanced flowering could be achieved for some species by specific storage regimes. In conclusion, the investigated species displayed a great potential for an energy saving production system as well as for enriching the autumn/winter pot plant assortment in Europe.