Preventing Premature Bud Drop

December 12, 2003 - 08:41

Evaluation of 1-MCP for prevention of premature bud drop in Impatiens wallerana, double impatiens and New Guinea impatiens.

In recent years, sales of impatiens -- Impatiens
wallerana
, double impatiens and New Guinea
impatiens -- have been phenomenal. However, one problem with impatiens is
premature flower and bud drop, which can be induced by ethylene, low light
conditions, water stress and other conditions. Furthermore, the abscised buds
and flowers are sources for infection by disease and infestation of insects in
greenhouses and retail stores, and the reduced bud count decreases the
aesthetic value of the plants.

1-methylcyclopropene (MCP) is a newly registered plant growth
regulator that is an organic gas with anti-ethylene effects, currently
available commercially under the trade name EthylBloc (Floralife, Inc.). The
compound does not leave residue on the plants. MCP has been evaluated in many
flowering plants and has been shown to protect against ethylene-induced petal
and flower drop in these and other crops. In impatiens, 1-MCP has been shown to
completely overcome flower abscission induced by exogenous ethylene. While it
is very exciting to know that this new compound can protect plants against
exogenous ethylene, ethylene can be excluded from display areas and thus does
not pose a major threat in the retail outlet. In impatiens, however, growers
often encounter premature bud and flower drop induced by environmental or
cultural conditions, and it would thus be critical to evaluate the possible use
of MCP for protection under these circumstances.

Grower Implications

Results of this study demonstrate that the water stress
often imposed on impatiens in the greenhouse and retail outlet caused bud drop
in double impatiens and not in Impatiens wallerana style='font-style:normal'>. Prolonged holding of plants (all three types of
impatiens) in an interior environment and boxing plants for transportation
induced bud drop. The stress-induced premature bud drop was reduced by
pre-treating plants with MCP.

Results and discussion

Impatiens wallerana
were propagated by seed, whereas New Guinea impatiens and double impatiens were
obtained from Color Links. Plants were planted in 4-inch containers filled with
Pro-Mix (Premier Horticulture) and were grown in the glasshouse at the
University of Massachusetts until flowering, at which time they were subjected
to either light and/or water stress. The low-light condition was set up to
simulate plants moved from a greenhouse to an interior retail outlet, whereas
the water stress was set up to mirror the wilting of plants often observed in
greenhouses as well as in retail stores. A low-light condition was obtained by
moving flowering plants into a 70º F laboratory illuminated 12 hours a day
with cool white fluorescent lamps. Water stress was provided by allowing plants
to wilt in the greenhouse before watering them again. Half of the plants were
pre-treated with MCP prior to being exposed to the stress whereas the control
plants were not treated with any chemicals. The degree of wilting was monitored
by measuring the soil moisture content. The number of buds abscised from each
plant was monitored. Furthermore, simulated long-distance shipment was
conducted by placing flowering plants in boxes for different durations (zero,
three or five days) followed by evaluation in the interior environment
mentioned above. Half of the plants were pre-treated with MCP prior to placing
them in the box whereas the controls were left untreated. The number of flowers
that opened and buds that prematurely abscised from each plant were monitored.

Impatiens wallerana

Low light condition.
Premature bud drop occurred when plants were held in an interior environment
for more than five days (see Figure 1, left). Bud drop increased rapidly during
the second week. Pre-treatment with MCP reduced bud drop but the benefits of
the MCP treatment was not realized until the plants had been held in the
low-light condition for more than one week. In addition, the size of the open
flowers were significantly Á smaller when plants were held in the
low-light environment, presumably due to limited carbohydrates required for the
development and opening of the flowers.

Water stress.
Wilting of plants in the greenhouse (soil moisture content was approximately
equal to 45 percent at the time of wilting) did not induce significant bud
drop. In all three cultivars evaluated, bud drop on each plant was less than 10
with most of the plants losing less than three buds during a three-week period
following the water stress (see Figure 3, page 59). However, growth of the
wilted plants in the Dazzler series (PanAmerican Seed) was affected by the
water stress and the plants weighed less than the non-wilted plants four weeks
after wilting, although visually, the differences were not detectable.
Treatment with MCP had no effect in the water-stress-induced growth reduction.

Simulated transportation. Placing plants in cardboard boxes for three or five days
significantly induced premature bud drop. Pre-treatment with MCP significantly
reduced bud drop and should be used in long distance transportation of potted
impatiens.

Double impatiens

Low light condition.
Low light induced rapid and large numbers of bud drop in double impatiens. Thirty
to 50 percent of the buds had dropped by day five in the interior environment.
Pre-treatment with MCP delayed the onset of bud drop, and no bud drop occurred
until after holding the plants in the low-light condition for a week. If plants
are to be held longer than one week, a second application of MCP would further
delay the onset of bud drop. A third treatment with MCP would not be necessary,
as additional benefits from that treatment were not observed.

Water stress.
Wilting of double impatiens yielded variable results. In one study, up to 25
percent of the buds abscised within three weeks after the wilting of 'Fiesta
Pink Ruffles' (Ball Floraplant) whereas in another study on 'Fiesta Ole
Cherry', less than 4 percent of the buds abscised. Comparison of the soil
moisture content showed that the soil moisture content in the former was lower
to 46 percent before water was applied whereas the soil moisture content in the
latter was 56 percent. Visually, both cultivars appeared to wilt to the same
level, although the available water content was quite different. We suspect
that the variable result on bud drop was a result of the differences in the
soil moisture content at the time of wilting. Data on bud abscission indicated
that bud drop continues many days after the wilting (see Figure 4, page 59). In
addition, wilting is associated with an increase in plant death and should be
avoided.

The effects of MCP were unclear. In the study where
significant bud drop occurred following wilting, MCP significantly reduced bud
drop. Whereas, in the other study in which wilting did not induce bud drop, MCP
had no additional benefits (see Figure 4, page 59) investigation on the
beneficial effects of MCP on double impatiens should be investigated prior to
making a sound conclusion.

Simulated transportation. A 3- or 5-day storage in cardboard boxes induced massive bud drop in
double impatiens with 20 and 60 percent of the buds abscised, respectively,
within four days after removing plants from the boxes (see Figure 2, page 58).
Pretreatment with MCP significantly reduced bud drop suggesting that all double
impatiens intended for boxing would benefit from a pretreatment with MCP and
emphasizing the importance of removing plants from the boxes as soon as they
reach their destination.

New Guinea impatiens

Low light condition.
Regardless of cultivar, bud abscission began 4-5 days after placing the plants
in an interior environment. Treatment with MCP before placing the plants in the
low-light environment significantly delayed and reduced bud abscission.

Simulated transportation. Storage in boxes greater than three days induced bud abscission with
approximately 20 percent buds abscised within five days after removal from the
box. Boxing for three days induced some bud abscission. MCP treatment before
storage reduced abscission indicating that plants intended for long distance
marketing should be pre-treated with MCP.

Summary

Generally speaking, double impatiens are more susceptible to
stress-induced bud drop than Impatiens wallerana and New Guinea impatiens. Low light (typical in an interior
environment) and prolonged boxing induced premature bud drop, which could be
reduced by pretreating the plants with MCP. Wilting of plants in the
greenhouse, a common cultural practice either to restrict growth of the plants
or by negligence, resulted in massive bud drop in double impatiens when soil
content dropped to approximately equal to 45 percent. Treatment with MCP help
reduce bud drop but to a limited extent. In contrast,
Impatiens
wallerana
tolerated wilting well and did
not drop large numbers of buds. Data taken four weeks after wilting, however,
showed that wilting reduced the subsequent growth rate of plants. style="mso-spacerun: yes"> 

This article was reprinted with permission of Floriculture
Industry Research and Scholarship Trust.

About The Author

Susan Han is associate professor at the University of Massachusetts, Amherst, Mass. She can be reached by E-mail at susanh@umext.umass.edu

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