Agriculture Reference
In-Depth Information
Certain cut flower species suffer physiological disorders,
some of which are caused by ethylene, low temperature,
gravitropic bending and phenol oxidation (Halevy & Mayak
1981; Wills et al . 1998; Reid 2002, 2004). Exposure to
ethylene often results in bud and flower abscission or accele-
rated senescence (Cameron & Reid 1981; Mor et al . 1984;
Woltering 1987; Woodson & Lawton 1988; Reid et al . 1989;
Joyce et al . 1990; Joyce 1993; Sexton et al . 1995; van Doorn
2001; Plate 19.1). Ethylene is also involved in the gravitropic
tip bending response of cut flowers, including snapdragon
and gladiolus (Woltering 1991; Philosoph-Hadas et al .
1996a; Philosoph-Hadas et al . 1999; Reid 2002).
Exposure to low temperatures above the freezing point of
flower tissues can cause chilling injury (Wills et al . 1998;
Reid 2002). Flowers of tropical and subtropical origin (e.g.
anthurium; Paull 1987) tend to be most susceptible to
chilling. The severity of chilling injury is a function of
increasing exposure times and/or falling temperatures.
Symptoms, which may only express upon return to ambient
temperatures, include tissue discolouration (i.e. blueing,
browning and blackening) and reduced vase life (Paull 1987;
Joyce & Shorter 2000; Miranda et al . 2000; Plate 19.1).
Gravitropic bending occurs when actively growing
regions of the cut flower grow upwards away from gravity
(e.g. in gladiolus, gerbera and snapdragons). The mecha-
nism appears to involve auxin redistribution, asymmetric
ethylene synthesis and changes in calcium levels (Philosoph-
Hadas et al . 1996a; Philosoph-Hadas et al . 1999 ) .
Phenol oxidation, leading to black leaves, is a major
problem in some protea species after harvest, particularly
when the flowers are kept in the dark. It is associated with
a loss of sugars from the leaves. It is probable that if sugars
are hydrolysed from phenolic glycosides the remaining
phenolic molecules are rapidly oxidised (Jones et al .
1995b). Blackening can sometimes be inhibited by feeding
glucose to the cut stems (Stephens et al . 2001).
Some flowers are damaged by fluoride in the water
supply (approximately 1 ppm). Fluoride accumulates in the
petal margins and kills those cells, as found in gerbera,
gladiolus, freesia and roses (Halevy & Mayak 1981; Tjia
et al . 1987).
Ultrastructural changes accompany the physiological
changes after harvest, such as tonoplast invagination and
breakdown, chloroplast and chromoplast breakdown,
disappearance of ribosomes and lipid phase separation in
membranes (Halevy & Mayak 1981; Thompson et al .
1997; Rubenstein 2000). While some of these changes may
be late events in cell death, there are some cases where
these changes occur before climacteric ethylene production
and before flower opening (Rubenstein 2000).
Water relations
All cut flowers can suffer from water deficit both in the
vase and beforehand (Halevy & Mayak 1981; Mayak 1987;
van Doorn 1997; Wills et al . 1998; Reid 2002, 2004).
Water loss is via stomata and trans-cuticular diffusion from
leaves and floral organs. The lower the vapour pressure of
the surrounding atmosphere, the steeper the diffusion
gradient for water loss (Wills et al . 1998). High airflow
rates favour water loss by disturbing the otherwise unstirred
water vapour boundary layer around the stems.
For flowers in vases, factors that limit water flow up
through the stem contribute to development of tissue water
deficits (van Doorn 1997). These factors can include: (1)
Blockage of stem ends and xylem elements by microbes
(Zagory & Reid 1986; van Doorn et al . 1989, 1991b); (2)
blockage due to physiological plugging (Parups & Molnar
1972; Lineberger & Steponkus 1976; van Doorn et al .
1991a; van Doorn & Cruz 2000; van Doorn & Vaslier 2002;
Williamson et al . 2002; He et al . 2006); (3) blockage caused
by physical plugging from organic (e.g. dead microbes)
and  inorganic (e.g. clay) particles in the vase water; and
(4) blockage by air bubbles formed in the xylem system
(i.e. cavitation), including at the stem ends (i.e. emboli)
(Dixon et al . 1988; van Meeteren 1992; van Doorn & Otma
1995; Williamson & Milburn 1995). Air emboli and xylem
cavitation can also occur in flower stems held out of
solution, such as during storage and/or transport.
Cut flowers lose water through stomata and cuticles. In
some flowers, stomata close after cutting. Post-harvest
light increased water loss in roses, presumably due to
stomatal opening (Halevy & Mayak 1981). The difference
in vase life between a short and a long-lived rose cultivar
was attributed to stomatal closure and reduced transpiration
in the long-lived cultivar (Mayak et al . 1974).
Water deficit stress experienced either prior to harvest
or  during storage, transport and vase life can enhance
senescence processes in cut flower tissues (Mayak &
Halevy 1971; Mayak et al . 1974; Spikeman 1986; Hinesley
1988; Drory et al . 1992; van Doorn & Suiro 1996).
Pests and diseases
Insect pests of cut flowers include those that visibly
damage flowers, detract from the appearance of flowers
and/or constitute a quarantine risk (Seaton & Joyce 1988;
Hansen & Hara 1994; Wills et al . 1998). The larvae of
many lepidopterous (moth and butterfly) species eat bud
and flower tissues. Early infestations of sucking insects,
such as mites, aphids, scales and mealy bugs, result in
flower spotting and/or deformation. Later infestations tend
to be less damaging to the flowers, but detract from their
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