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Bacterial growth and stem water relations in cut flowers


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Jeang, PS 2000 , 'Bacterial growth and stem water relations in cut flowers', Research Master thesis, University of Tasmania.

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Longevity of vase life is a significant quality parameter in the cut flower
industry. A number of factors have been postulated to influence longevity of
vase life, and many of these involve disruption to water relations within the
stem, particularly increased hydraulic resistance as a result of air embolisms,
physical occlusions in the xylem vessels or bacterial interference. The purpose
of this study was to the investigate the role of bacteria in disrupting hydraulic
resistance in the stems of three important cut flower species.
Xylem vessel length distributions of carnation, iris and chrysanthemum were
determined, the maximum vessel length of each flower species being less than
4, 1 and 6 em respectively. Stem sections longer than these vessel lengths were
then used to determine the relationship between bacterial number and
hydraulic resistance in various parts of the stem. Bacterial populations
increased in all parts of the flower stem during the vase life period. The
largest populations were found in the basal section of stems, particularly
within 2 mm from the cut surface. The basal section was also the site of
highest stem hydraulic resistance. However, only a very weak correlation
existed between bacterial numbers in various parts of the stem and hydraulic
resistance. Furthermore, bacterial cells were found to travel higher up the
stem than the length of the longest vessels, indicating that the bacterial cells
were unlikely to be the major cause of occlusions at intervessel pits. Xylem
occlusion was more likely to be located at or close to the stem cut surface as
removal of a 5 mm segment from the stem base resulted in significantly
decreased hydraulic resistance.
Positive correlations were obtained between stem hydraulic resistance and
concentrations of a bacterial exudate, bacterial exopolysaccharide (EPS), which
was found to be present primarily at the base of the stem. Bacterial exopolysaccharides were also fotmd in xylem vessels further up the flower
stem but distribution was generally restricted to a small number of vessels. In
contrast, the bacterial EPS at the base of cut flower stems covered all cut
vessels within 2-4 days of vase life. Bacterial EPS extracted from cultured
bacterial cells was fotmd to significantly increase hydraulic resistance when
attached to filter paper disks covering one end of a section of open tubing. The
degree to which EPS caused increased hydraulic resistance was fotmd to be
influenced by the substrate on which the bacteria were established suggesting
that EPS composition influenced its capacity in induce hydraulic resistance.
Non-EPS producing bacteria were found to have minimal effect on hydraulic
resistance in the filtered tubing section, even when applied in greater bacterial
cell concentrations than EPS producing bacteria. It was concluded that
bacterial exopolysaccharides play an important role in the development of
hydraulic resistance arotmd the stem cut surface, thus restricting water uptake
and shortening cut flower vase life. The results of this study provide a basis
for further research which may lead to substantial improvements in postharvest
techniques for the cut-flower industry.

Item Type: Thesis - Research Master
Authors/Creators:Jeang, PS
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Copyright 2000 the Author-The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

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