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ISHS Acta Horticulturae 694: International Symposium on Harnessing the Potential of Horticulture in the Asian-Pacific Region

EFFECT OF SHADE ON BRACT BROWNING OF WARATAHS (TELOPEA SPP.)

Authors:   R. McConchie, A. Martyn, C. Offord
Keywords:   Anthocyanin, bract burn, chlorophyll, cut flowers, microclimate, photoinhibition, UV-B absorbance
Abstract:
Browning of the attractive floral bracts surrounding the waratah inflorescence severely reduces cut flower quality. In 2002 and 2003, ‘Fire and Brimstone’ and ‘Olympic Flame’ waratahs were grown under 50% black shade cloth or in full sun. Some plants were shaded from bud development in January (early shading), while others were shaded from bud opening in July (late shading) until harvest in September or October. Floral bract browning was significantly reduced by growing waratahs under 50% shade cloth, compared to full sun. Waratah bracts were less photosynthetically efficient than leaves, indicating greater potential for photoinhibition. By flower maturity, waratah bracts exposed to full sun had significantly lower photosynthetic efficiency, indicating chronic photoinhibition was occurring. Treatment with 50% shade cloth reduced photoinhibition as well as browning. Bracts on late-shaded flowers tended to have a higher photosynthetic efficiency than early-shaded or sun exposed flowers. The physiological cause of browning will be discussed, implicating chronic photoinhibition and oxidative damage following light stress. These results indicate that waratah quality may be improved by managing the crop to avoid excess light and other stressors that can lead to chronic photoinhibition and browning, particularly from bud opening onwards.
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