Using Gibberellins to Prevent Leaf Yellowing in Cut Lilies

January 16, 2002 - 13:01

Whether applied as a pulse, leaf/stem spray or vase solution component, new research at Cornell University is showing that gibberellins can decrease dead or yellow leaves and increase flower longevity in cut lilies.

Hybrid lilies are excellent cut flowers due to the
availability of flowers with various colors and shapes. Extensive inter-species
hybridization has resulted in numerous cultivars, and many new cultivars are
introduced to the market each year. While the vigor and reliability of the crop
has improved over the years, what has not changed is that successful use
depends on the postharvest quality of the cut stem.

The postharvest performance of cut lilies is dependent on
many factors, such as the cultivar, preharvest conditions, stage of harvest,
and postharvest environment and handling. Vase life of the cut stem usually
ends when flower petals wilt or turn brown, but leaf quality is another
important postharvest aspect. In many, if not most, hybrid lily cultivars,
leaves start to turn yellow well before the end of the inflorescence life,
making the stems less attractive. This is especially true if the stems have been
cold-stored for any length of time prior to marketing. Generally, the vase life
of cut lilies varies from 5-14 days, depending on the cultivar.

The potential use of growth regulators, especially
gibberellins and cytokinins, has not been studied adequately in cut lilies. Our
previous studies have shown that spray treatments with GA4+7 alone or in
combination with BA (i.e., Fascination, Valent USA) remarkably reduce
cold-induced leaf yellowing in pot hybrid lilies and gradual leaf yellowing in
Easter lilies. We have also seen positive effects on flower longevity in these
hormone-treated plants. These observations warranted the investigation of
potential use of these chemicals in cut lilies.

This research was carried out to investigate the potential
use of gibberellins and benzyladenine (BA) to improve postharvest quality of
cut hybrid lilies. Experiments were conducted using various cultivars from
different groups of hybrid lilies to test different aspects of treatment, such
as the concentration, method of application and time of application. We want to
emphasize that this is a research report and that the chemicals evaluated in
this project are not currently labeled for use on cut lilies. Please contact
your chemical representative before any new usage and always follow chemical
labels.

Experiments

Experiments were conducted with a range of commercially
important cultivars of Oriental, Asiatic and LA-hybrid lilies. Cultivars tested
include Asiatics ‘Amarone’, ‘Colosseo’,
‘Marseille’, ‘Orandiso’, ‘Vermeer’ and ‘Vivaldi’;
Orientals ‘Berlin’, ‘Helvetia’, ‘Muscadet’,
‘Tom Pouce’, ‘Star Gazer’ and ‘Sissi’; and
LA-hybrids ‘Cebeco Dazzle’, ‘Fangio’, ‘Royal
Parade’, ‘Royal Perfume’ and ‘Samor’. Plants were
grown in Á bulb crates with MetroMix 360 in Cornell University greenhouses
according to standard cultural practices. Stems were cut at the commercially
acceptable maturity for experiments from May-July.

In most cases, growth regulator treatments were done
immediately after harvest. Compounds used included: ProGibb (GA3), Provide
(GA4+7), BAP-10 (benzyladenine, BA) and Fascination (contains an equal, 1:1
ratio of GA4+7 and BA).

Several experiments were conducted to investigate factors
such as compound, concentration, method and duration of application (pulse,
foliar spray or inclusion in vase solution).

After the treatments, stems were either transferred directly
to a postharvest evaluation room (68° F with typical “indoor”
fluorescent light at 12 hrs per day) or stored (dark, on water) at 36-37° F
for up to two weeks prior to the transfer to the postharvest evaluation room.
The standard vase solution in the postharvest room contained 3 percent sucrose
and 200 ppm 8-hydroxyquinoline citrate.

Data on leaf quality (percentage yellow or necrotic leaves)
and inflorescence longevity (time of wilting of the last open flower of the
inflorescence) were recorded at regular intervals in the postharvest room, up
to three weeks. Á

Results

Cultivar differences.
Cut lily stems of most of the evaluated cultivars started showing symptoms of
leaf yellowing approximately one week after placement in the postharvest room
(well before the end of inflorescence life). This leaf yellowing was
accelerated when stems were stored at 36-37° F for up to two weeks after
the cut. Oriental, Asiatic and LA-hybrid cultivars varied greatly in their
potential for leaf yellowing during postharvest evaluation (See Table 1).
Overall, oriental cultivars tended to show more yellowing after the 2-week
evaluation. Even so, the Oriental ‘Tom Pouce’, Asiatic
‘Vivaldi’ and the LA ‘Cebeco Dazzle’ showed less than
20 percent yellowing, even if the cut stems had been stressed by holding dark
for two weeks on water, at 36-37° F prior to evaluation.

Method of application.
GA4+7 was effective whether applied as a stem uptake (pulse) treatment, as a
leaf/stem spray after harvest or as a vase solution component (See Table 2).
For example, after two weeks in the postharvest room, the three cultivars used
had 16-41 percent dead or yellow leaves, whereas plants with any of the treatments
had less than 5 percent yellow leaves. Another general effect of gibberellin on
lilies is an increase in flower longevity. For example, with ‘Star
Gazer’, one can see flower life increasing from 12 to 14 days with
gibberellin treatment. Á

Active compound.
GA4+7 can also be seen to be the active component of the treatment, as GA4+7
applied individually was at least as effective as the combination of GA4+7 and
BA (See Table 3). This is the same finding as we have seen in Easter lily and
in potted Oriental hybrid lilies. Table 4 gives a further comparison of GA4+7
and GA3 in the LA-hybrid cultivar ‘Cebeco Dazzle’. While both
GA’s are effective in increasing flower life, only the GA4+7 is active in
preventing leaf yellowing.

Pulse duration and temperature. style='font-weight:normal'> There appears to be wide latitude regarding
concentrations, temperature and duration for GA4+7 pulses. Table 5 shows that a
6-hour pulse at 37° F was as effective as an 18-hour pulse at 68° F. In
this preliminary experiment, we did not measure solution uptake but assume that
much more uptake occurred with the longer and warmer treatment.

GA4+7 concentration.
In another experiment with the Asiatic cultivar ‘Orandiso’, GA4+7
pulses at 25 ppm were equally effective as pulses at 100 ppm. There are,
however, upper limits to GA4+7 use. In this experiment, the Asiatic cultivar
‘Marseille’ was subjected to water or long pulses of GA3 or GA4+7
at 100 or 500 ppm. The higher concentration of GA4+7 was phytotoxic to the
plants and caused complete death. While this appears to be an extreme example,
additional experiments need to be conducted to further define these parameters
as they relate to commercial situations.

Gibberellins also prevented leaf yellowing in cut lily stems
when included as a component in the vase solution. Effective concentrations of
GA4+7 were 5-25 ppm. These treatments were also effective in the case of
cold-stored stems.

About The Author

Drs. Ranwala and Miller are in the Department of Horticulture, Cornell University, Ithaca N.Y. They can be contacted via E-mail at wbm8@cornell.edu.

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