Executive Summary
Background
Current exports of Australian cut flowers concentrate
on only a few of numerous genera. If the borderline vase lives (i.e. <
7 days) of many Australian flowers could be improved, the range of species
available for export might increase. This project hypothesised that when
flowers are cut, their response to that mechanical damage was to deposit
an hydrophobic substance (suberin). A general response to any mechanical
damage to plant tissue is suberin formation. A suberin barrier is formed
as a generic response to wounding, e.g. to seal off an area invaded by
a pathogen. If this occurred in cut flowers, the suberin barrier could
cause premature wilting and a shortened vase life because stems were no
longer able to take up water from the vase solution. Several chemicals
are known to inhibit suberin formation, and these were tested on a number
of Australian wildflowers.
Objectives
This project was aimed at enhancing the export reputation
of Australian native cut flowers and increasing the number of exportable
species, with the following objectives:
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to counteract the poor water uptake that characterises most
Australian native cut flowers with borderline vase lives (i.e. < 7 days)
by inhibiting the initial postharvest wounding response;
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to determine whether suberin inhibiting treatments could
be used to enhance water uptake and increase the vase life of selected
Australian native flowers;
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to ascertain by Transmission Electron Microscopy whether
suberin is deposited in cut stems; and
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to ascertain whether any other factors, such as ethylene
sensitivity, are involved in a particular flower’s senescence.
Research outcomes
The major outcomes of this research were:
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The first recorded evidence showing the wounding response
in cut flowers under the transmission electron microscope (TEM). The observed
alteration of pit membranes was indicated by changes in electron density.
Such a response is the first part of a two stage suberisation process known
to occur in trees as a response to injury or pathogen invasion.
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The wounding response observed under TEM was inhibited by
the chemical, S-carvone. This chemical is known to delay the appearance
of suberin in potato tubers. S-carvone significantly increased the vase
life of Hakea francisiana, the only species tested with it.
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Vase life was significantly increased by keeping cut stems
in deep water rather than in shallow water. This occurred in all three
species tested: Acacia baileyana, Leptospermum obovatum and
L. polygalifolium. The beneficial effect of high water is likely
to be the result of increased hydrostatic pressure on the stem, but whether
that pressure dissolved air emboli or pushed through a suberin barrier
is not known.
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Daily removal of the basal 1 cm from stems significantly
increased the vase life and water uptake of the three species listed above.
When these results are considered with the TEM results, it appears likely
that recutting removes the early stages of a wounding response. This wounding
response can eventually lead to suberin deposition, as mentioned above.
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The vase life results of some species indicated the possible
involvement of ethylene in their senescence. As a result, ethylene sensitivity
was determined in Baeckea virgata, Crowea exalata and Lophomyrtus
ralphii ‘Krinkly’.
Recommendations
Several recommendations can be made, both to industry
and for future research, as a result of this project:
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More TEM work needs to be done, e.g. a daily time course
of wounding responses to see whether suberin does eventually form, and
the examination of other species, especially short-lived and long-lived
cut flowers.
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S-carvone needs to be tested on other species to see whether
it increases their vase life and also whether a short-term pulse will translate
to long-term inhibition of the wounding response; Daily recutting of stems
will inhibit the full effects of a wounding response. It could possibly
delay the effects of suberin formation and the impaired water conduction
that may result.
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A practical, easy way to improve vase life is by standing
stems in deep water. This can be done at the packing shed.
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Several Australian flowers of commercial and export importance
are sensitive to ethylene and therefore should be treated and/or protected
against its effects in order to attain optimum vase life: Baeckea virgata,
Crowea exalata and Lophomyrtus ralphii ‘Krinkly’.
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Several species used in this project were not tested for
ethylene but indications are that they may be sensitive to it. Furthermore,
there are dozens more commercially important cut flower species that need
to be tested because if they are ethylene sensitive, treatment can provide
an easy way to significantly increase vase life.
Last updated: 9 October
2002
Copyright RIRDC
http://www.rirdc.gov.au/reports/WNP/02-114sum.html
