Long Term Production of Rose Flowers in the Greenhouse under different Cooling Methods: II. Responses of the Flower Bud

The objective of the study was to determine the responses of rose flower buds to aerial environmental conditions. Since environmental conditions may affect various plant organs differently, it was important to determine the contribution of these organs to bud development. Rose plants were grown in a greenhouse in southern Israel for three years under different cooling systems throughout the summer. Evaporative cooling with a wet pad was the most effective system for preventing a decline in plant water potential, mainly during midsummer. Water potential of the flower bud was higher than that of the stem, regardless of season and treatment. The season of flower development had the most marked effect on flower bud fresh weight. Night cooling during spring and early summer was the only treatment that provided a slight increase in flower bud weight and in its relative weight out of the total flower weight. The increase in flower bud diameter was nearly linear with time, regardless of season, while stem elongation was logarithmic and then leveled off. The development of both organs extended much longer in the winter than in the summer, resulting in longer stems and larger buds. A mechanistic model was developed in order to determine the relative contribution of various organs to the bud. The flower stem and leaves contributed 50 to 67 % of the final bud dry weight, while the rest was comprised of the bud sepals, small bent branches and structural branches. The contribution by the bud sepals, was markedly enhanced, by night cooling. Fresh weight of the flower bud was highly correlated with flower leaf area and weight (including stem weight) but not with stem length. Gegenstand der Untersuchung war, die Reaktionen von Rosenblütenknospen auf atmosphärische Bedingungen im Gewächshaus zu ermitteln. Da diese Umweltbedingungen vermutlich unterschiedlich stark auf die einzelnen Pflanzenorgane einwirken, war es wichtig den Beitrag, den diese Organe zur Knospenbildung leisten, zu untersuchen. Hierfür wurden im Süden Israels drei Jahre lang Rosen in Gewächshäusern kultiviert, die während des Sommers mittels unterschiedlicher Methoden gekühlt wurden. Verdunstungskühlung mit Kühlmatten war die wirkungsvollste Methode, um vor allem im Hochsommer einen Rückgang des Pflanzenwasserpotentials zu verhindern. Das Wasserpotential der Blütenknospen war unabhängig von Jahreszeit und Behandlung höher als das der Stängel. Die Jahreszeit, in der sich die Blüten entwickelten, hatte den de