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  • Author or Editor: M. Oren-Shamir x
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Changes in temperature during rose flower development, often cause a significant fading of flower color, decreasing its market value. We are studying the effect of transient high temperature stress on red roses (Rosa ×hybrida, `Jaguar'). We have found that a transient temperature stress of 39/18 °C day/night respectively for 3 days, in comparison to the growth temperature of 26/18 °C, caused a significant fading to flower color at a mature bud stage. The plant organ responsible for color fading is the flower bud only. When the stress was applied to the whole plant, not including the flower buds, there was no change on the mature bud color. We have also shown that there are specific flower developmental stages sensitive to the transient increase in temperature. Flower buds at the critical stage of development, that have been exposed to temperature increase have a faded pink-red color when matured. Total anthocyanin levels of faded flowers, due to temperature stress, decreased to ≈50%. In addition, the ratio between the two anthocyanidins composing the red color, cyanidin and pelargonidin, changed dramatically due to the temperature stress: flowers on plants that have not overcome a temperature stress had a ration of 1:1, while those that have faded due to the temperature stress have a ration of 2:1 of pelargonidin to cyanidin, respectively. These findings hint to specific stages of anthocyanin synthesis, that are hypersensitive to increased temperature. We are now in the process of identifying and characterizing these stages.

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Little is known about the effect of growth temperature on Aster (Compositae, Asteraceae) flower development. In this study, we report on this effect for two aster lines, `Suntana' and `Sungal'. Growth temperature had a dramatic effect on the duration of flower development, ranging from 22 days for plants growing at 29 °C up to 32 days for plants grown at 17 °C. Flower longevity was ≈40% shorter under the higher temperature for both lines. Growth temperature also affected flowerhead form: `Suntana' flowerhead diameter was 20% larger at 17 °C than at 29 °C. The number of `Sungal' florets per flowerhead was four times greater at the lower temperature. Shading (30%) under temperature-controlled conditions had no effect on any of the parameters measured. For plants grown outdoors, our results suggest that shading plants may increase quality by reducing the growth temperature.

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Many green-decorative branches (“Greens”) and cut flowers are commercially grown under shade nets, for both the reduction of the natural intercepted sunlight as well as physical protection. The most commonly used are black nets, which do not affect the visible light spectrum. In the work presented here we have studied the effects of shade nets of varying optical properties on the vegetative and flowering responses of ornamental plants, searching for nets that will specifically induce a desired behavior, thus gaining benefits in addition to the mere shading. Nets of different transmittance spectra, light scattering, reflectance and thermal properties are being studied for their effect on the vegetative growth of several Greens: Pittosporum variegatum, Ruscus hypoglossum, and Leather-leaf fern. The knitting density of all nets has been adjusted to have the same percent shading in the PAR (photosynthetically active radiation) range of the spectrum for all nets investigated. Experiments were carried out in commercial plots. Data were collected for microclimate, physiological and horticultural parameters. The main results obtained so far: i) pronounced stimulation of the vegetative growth under the Red net; ii) dwarfing by the Blue net; iii) the Grey net markedly enhanced branching, yielding “bushy” plants with short side branches; iv) the reflective, thermal net (Aluminet®) enhanced side, long branching (in Pittosporum). Recently we have applied a similar approach to cut flowers such as Lupinus luteus, Lisianthus eustoma, and Dubium ornitugalum, and obtained dramatic effects of some of the nets on both the vegetative development and flowering behavior. The results to be presented, suggest that sophistication of the use of shade nets can lead to better agricultural performance.

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