Agriculture Reference
In-Depth Information
pH 3 also suppresses microbial development, but should not
be used in combination with chlorine (Xie
et al
. 2008).
PRESERVATION
Cut flowers and foliage are often processed from fresh to
more durable forms for use in the florist trade (Plate 19.6).
The processes are generally simple and include drying,
sulphuring, bleaching, dyeing and treatment with
humectants (Joyce 1998).
Food
Sugar, 0.5% to 2.0% sucrose, can be provided in vase
solutions to sustain flower development processes
(Ichimura 1998; Halevy & Mayak 1981; Reid 2002, 2004).
Optimum concentrations vary with the genotype and
flower development stage. Bud opening typically requires
higher concentrations, up to 5%, to meet respiratory and
osmotic demands.
Drying
Dried cut flowers are called 'everlastings' in some parts of
the world. A number of approaches can be taken to drying
cut flowers and foliage (Knap 1975; Petersons 1981;
Dubois & Joyce 1989a; Joyce 1998). A very common
method of drying is simply to suspend bunched cut
flowers upside down from rafters or racks in an airy shed.
Ventilation of black plastic-covered tunnel houses, with
air piped through a matrix of vented plastic drainage
pipes, is an inexpensive means of drying on a commercial
scale. Air can be de-humidified to speed the dehydration
process. Freeze drying (lyophilisation) is also possible,
but is expensive relative to the low unit value of the
product. Physical support for the material being dried can
be provided with a view to minimising distortion. On a
limited scale, plant material can be dried in a bed of dry
sand or silica gel. Microwave oven drying in a bed of pre-
dried silica gel also offers physical support. The pressing
of cut flowers between sheets of newsprint that are
regularly changed has long been practised.
Ethylene
Ethylene can cause flower fall or senescence of sensitive
cut flowers (Halevy & Mayak 1981; Reid 2002; Reid
2004). These flowers should ideally have been pre-treated
with either inhibitors of ethylene-mediated processes (e.g.
auxin), ethylene production (e.g. AVG, AOA) or,
preferably, inhibitors of ethylene action (e.g. STS,
1-MCP). Inhibitors of ethylene synthesis (AOA, AVG)
have been used in some vase solutions for flowers that
produce their own ethylene, such as carnations. However,
they are generally less effective than STS or 1-MCP.
Sources of ethylene, such as ripening fruit and car
exhausts, should be avoided. Ventilation with fresh air is
an effective and inexpensive solution to ethylene
contamination problems.
Plant growth regulators
PGRs can be used to help maintain the post-harvest
longevity of certain cut flowers (Halevy and Mayak 1981).
In laboratory experiments, cytokinins extend the life of
carnations, roses and iris and delay leaf yellowing.
Gibberellins also delay leaf yellowing. Abscisic acid has
been used to reduce water use and leaf crisping of roses
and to extend the life of Geraldton waxflower foliage
(Halevy and Mayak 1981; Joyce & Jones 1992). In
commercial practice, most vase solutions do not contain
plant growth regulators. However, a small number contain
cytokinins and/or gibberellins specifically to delay leaf
yellowing.
Sulphuring
Sulphuring of fresh cut flowers can be achieved by
exposure in a confined space to SO
2
gas or the fumes
from burning sublimed sulphur powder (Joyce 1998).
This treatment bleaches some pigments like chlorophyll
and fixes others such as anthocyanins. In addition,
sulphuring speeds drying and helps prevent mould
growth. Sulphuring is particularly effective for red roses,
where the red of the petals and green of the leaves become
lighter. Sulphur is both toxic and corrosive and so care
must be taken in selection of application protocols and
treatment facilities.
Bleaching
Through bleaching, plant pigments are degraded or altered
leaving the tissue light and even white. Oxidative (chlorite)
and/or reductive (sulfite) bleaching can be used for cut
flowers (Dubois & Joyce 1988, 1992a; Joyce 1998).
Brittleness and yellowing may be reduced by multistep
bleach processing in which peroxide is followed by
chlorite. The pH of bleach baths needs to be adjusted to
optimise the process in terms of the rate of release of active
Other treatments
A number of lesser known treatments have been tested or
advocated for specific cut flowers (Halevy & Mayak 1981).
For example, ethanol in the vase solution can enhance the
vase life of carnations (Wu
et al
. 1992). Dipping stem ends
of Iceland poppy into boiling water can coagulate latex that
might otherwise block xylem uptake of vase water (Stirling
1950, cited by Halevy & Mayak 1981).
