Physiological and hormonal Factors Related to Longevity of Flowering Potted Plants 1992 Proposal
OF FLOWERING POTTED PLANTS
This project will investigate the physiological factors that affect
decline of flowering potted plants indoors. These factors involve
production practices, shipping and handling procedures, and indoor
environment as related to the grower, wholesaler, retailer and consumer
as related to internal changes in sucrose, glucose and fructose.
Our new greenhouse/laboratory facilities have thirteen environmentally
controlled interior simulation rooms for conducting postharvest research
on floriculture crops. This project has provided information on the
differences in longevity for several chrysanthemum and poinsettia
cultivars, the influence of fertilization and light level during production
on longevity and the importance of proper shipping and holding environments
for several floriculture species. Also, flower respiration after
17 days indoors has been related to longevity of several chrysanthemum
varieties, Our objective is to identify physiological parameters
related to increased longevity. The long range benefit of this work
is that all the industry will have a better understanding of how to produce
and handle floriculture crops to provide a more desirable product
that will last longer for the consumer.
INTRODUCTION AND BACKGROUND INFORMATION
Quality will characterize business success in the 1990s, according to
numerous consumer and marketing experts. The floriculture industry
is no exception! Flowering plants are in direct competition with
a multitude of other discretionary purchase items, and if floral sales
are to increase, consumers must be satisfied with the flowers they
buy.
In today’s market, florists and mass market buyers are demanding
flowering plants that demonstrate increased performance, as well
as attractive physical characteristics. Repeat consumer purchases
are discouraged by flowering plants that fade, wither and die under ordinary
interior conditions. So emphasis in the 1990s will focus on producing
plants that are durable, resilient and long lasting, as well as beautiful.
Today, 75 percent of pot mums are sold through supermarkets, according
to a recent study by Yoder Brothers. Floral buyers consider in-store
and in-home keeping quality to be among the most important attributes
in floral products.
Variation in production practices results in considerable variation
in longevity of flowering potted plants produced by different growers.
Modifying production and handling practices can improve flowering
plants for the consumer. Production environment, cultural practices and
variety significantly impact longevity and quality. Growers manipulate
production temperature and light levels to maximize root development,
increase branching and - with the use of DIF (relationship of day and night
temperatures) - control plant height, thus ensuring good production
quality. Research has demonstrated that growers can also use some
cultural and environmental conditions to increase postproduction quality
and longevity.
REVIEW OF SIGNIFICANT LITERATURE
Good growers build quality into their plants from the time they
select varieties until they ship plants from the greenhouse to the
retail store. Each decision about variety selection, cultural practices,
production environment, storage, transport conditions and retail environment
can have a major impact on plant longevity. Quality is achievable
by establishing the factors and conditions affecting quality and
then incorporating these specific criteria into production protocols. Achieving
quality doesn’t necessarily mean increasing cost.
Growers can virtually assure flowering potted plant longevity
by selecting varieties known to tolerate low interior light conditions
well. More resilient varieties have less bud and leaf drop and leaf
yellowing and increased flower longevity under interior conditions when
compared to other varieties (9). Interior longevity of chrysanthemum
varieties, for instance, may vary by as much as two weeks due to leaf
yellowing, flower fading or decline (13). Similarly, poinsettia leaf drop
varies from 20 to 90 percent over a 30-day interior period depending
on variety (11).
Production practices have long been oriented toward producing
plants sized to respond to designated markets. Product size will
continue to be important. But growers should be simultaneously modifying
environmental conditions and production practices to increase longevity,
as well. Modifying environmental conditions to improve interior longevity
doesn’t necessarily mean incurring additional production costs. Reducing
temperatures during the final two to three production weeks intensifies
flower and bract colors. If DIF is used to control plant height,
use of either a zero DIF or a slightly positive DIF during the final
two to three production weeks is best to enhance longevity (15). High night
temperatures during the final 2-3 weeks of a poinsettia crop may
contribute to bract edge burn since these temperatures promote rapid
bract enlargement.
Production light levels are also important in extending flowering
potted plant longevity (5, 9, 15). Unlike potted foliage plants where
a low light acclimatization period reduces leaf drop, work in the United
States and Europe has demonstrated that high light levels reduce bud drop
and increase interior performance of chrysanthemums, Christmas begonias,
poinsettias and other flowering plants (5, 9). Symptoms of low production
light levels include more flower and bud drop, premature cyathia drop and
shortened interior longevity. In the northern United States, using high
intensity lighting to optimize longevity during the winter months
may be essential to obtain plant size, as well as to develop a plant with
good longevity.
Fertilization practices affect longevty, also (6, 7, 8, 10, 12,
16). Reducing fertilizer levels increases longevity without affecting
plant marketability. In many cases, the amount of water applied at each
watering necessitates high fertilizer levels. Reducing fertilizer level
is difficult for some growers to accept initially, but growers who
have lowered fertilizer levels have increased postproduction longevity
without detrimental effects on crop marketability.
Our program at the University of Florida has investigated effects
of terminating fertilizer during the final two to three production
weeks (8). Stopping fertilizer applications during the final production
stages increased chrysanthemum longevity and reduced incidence of
bract edge burn of Gutbier V-14 Glory poinsettia (12). With Easter
lilies, however, preliminary work has indicated that fertilizer termination
isn’t beneficial, so fertilizer applications must be continued until
this crop is marketed to avoid premature leaf yellowing. Success
of fertilizer termination for each grower is determined by fertilizer levels
used, growing media and crop. Growers currently using high fertilizer
levels throughout the entire production period will experience greater
benefits than growers already using optimum fertilizer levels or reducing
fertilizer levels at the end of the crop. Basically, terminating
fertilizer reduces the soluble salt level in the growing medium and
prevents excessive elemental (salt) buildup in the plant. Nitrogen and
potassium sources used in fertilizer programs also affect longevity.
Longevity of most flowering potted plants is greatest when 60 to
70 percent of the nitrogen is from nitrate sources and the remainder from
either ammonium or nitrate sources (Roude).
Also, some growers have altered the nitrogen-to-potassium ratio
at the end of the crop to extend longevity. There doesn’t appear
to be any benefit from this procedure, but it may be beneficial to switch
from fertilizers containing ammonium nitrogen and low calcium and potassium
nitrate during the final two to three production weeks.
Growing medium also influences postproduction performance of flowering
potted plants. The medium should provide good aeration and nutrient
holding capacity during production and maximum water holding capacity
during postproduction to minimize drying out during retail and consumer
phases. Wetting agents applied at time of marketing allow for uniform
watering during postproduction thus, reducing moisture stress and
increasing longevity.
The research results summarized above demonstrate that growers
have numerous opportunities to improve longevity of flowering potted
plants. However, specific cultural modifications depend on plant
species and variety. Thus, it is imperative that the physiological and
hormonal changes involved in these responses be better understood
so that recommendations can be made for a large number of plant species.
For instance, in cut flowers, use of a sugar based preservative
is nearly a universal recommendation due to increased carbohydrate
supply to the flower. Similarly, light compensation point has been
a useful indicator of the interior performance of foliage plants. In flowering
plants, hormonal control of bud/flower drop in some species has been
related to ethylene (1, 2, 3, 4) but the role of carbohydrates is
unclear. In our previous work with hibiscus, poinsettia and chrysanthemums,
carbohydrate levels were not strongly related to flower longevity or bud
drop. However, respiration of chrysanthemum flowers was correlated
with flower longevity after 17 days under interior conditions - the
longest lasting varieties had the lowest respiration levels. These results
with chrysanthemum suggest a role of carbohydrates even though levels
of non-structural carbohydrates in long and short lasting varieties
were similar. Carbohydrate levels may be an indication that 1) sugars are
not being translocated from leaves and stems to the flower, 2) sugars
have little, if any, significance in flowering plant longevity, or 3)
presence of threshold levels in certain varieties which allow long lasting
varieties to more efficiently utilize available sugars. Identification
of the factors involved in flowering potted plant longevity will advance
the industry’s ability to provide better quality, longer lasting
plants to the consumer.
OBJECTIVES
1. To relate physiological parameters (photosynthesis, dark respiration,
carbohydrate levels, etc) to increased longevity of flowering potted
plants. 2. To identify cultural practices which improve flowering
potted plant longevity, as related to physiological or hormonal changes.
MATERIALS AND METHODS
A number of studies will be conducted with chrysanthemum, poinsettia
and potted rose as part of this project. Plants will be grown in
a fiberglass, fan and pad cooled greenhouse, or in air conditioned
greenhouses at the University of Florida, Gainesville, using standard commercial
production practices for each crop.
A. Factors related to cyathia bud drop Our work over the
last 2 years has related some differences in sucrose, fructose and glucose
levels in ‘Annette Hegg Lady’ and ‘Gutbier V-14 Glory’ to cyathia chop,
but a strong relationship was not present. In the current study,
we will expand this work using additional poinsettia varieties and
production conditions to further identify the factors involved in cyathia
drop.
1. Poinsettia plants will be grown to anthesis, then moved to
our interior rooms at standard conditions of 70 ft-c., 12 hours daily
and 70′F and 55% relative humidity. Carbohydrate and starch levels
will be related to cyathia bud drop at each sampling time. Cyathia, leaf,
stem and bract tissue will be collected at anthesis and weekly after plants
are moved into interior conditions. Samples will be oven dried at
70′C and then ground in a Wiley Mill. Sugars will be extracted from
the ground tissue by boiling in an 80% ethanol solution for 20 minutes.
The separation of fructose, glucose and sucrose will be performed by gas
chromatography techniques using trimethylsilylation derivatives.
2. Poinsettias ‘Lilo’, ‘Subjibi’ and ‘Freedom’ will be grown at
65′F night/75′F day and 72′F night/82′F day from planting to anthesis.
Cyathia buds will be collected and analyzed for carbohydrates as
outlined above. Cyathia bud drop will be determined weekly after
plants are moved indoors.
B. Relationship of Production temperature to carbohydrate levels
and longevity
Chrysanthemums ‘Tara’ and ‘Boaldi’ will be grown at 65′F night/75′F
day or 72′F night/82′F day from planting to flower. At flowering,
flower, stem and leaf samples will be taken for analysis of sucrose,
glucose and fructose using procedures outlined above. An additional group
of plants will be moved to interior rooms for evaluation of longevity.
This study will be repeated and additional samples taken for carbohydrate
analysis, pending the results of the first study.
C. Relationship of Supra-optimal carbohydrate levels to longevity
Potted roses and carnations will be grown to marketable stage
then moved to interior rooms. Carbohydrate levels will be boosted
in the plants by injecting sucrose into the stems either 1) during
the final 2 weeks of production, 2) during the entire interior period,
3) a combination of 1 and 2 or 4) no additional sucrose. Carbohydrate
levels, flower respiration, bud drop and flowering longevity will
be determined
FACILITIES AND EQUIPMENT AVAILABLE
The Environmental Horticulture greenhouses, laboratories, and
interior simulation rooms will be used for this project. Laboratory
facilities include 13 environmentally controlled postproduction rooms,
5 rooms for simulated shipping, and equipment for photosynthesis and respiration
measurements, carbohydrate analysis and colorometric procedures.
BUDGET
This project will include our work (T. A. Nell and J. E. Barrett),
R. T. Leonard (state supported
biological scientist assigned to Terril Nell), and two Doctoral
students.
Supplies, greenhouse and interior space, laboratory chemicals
$6000
Labor for assistance in growing plants, analyzing plant tissue,
and taking and analyzing data 9000
New columns/parts for gas chromatograph 1500
TOTAL 16,500
REFERENCES
1. Agnew, N. H, M. L. Albrecht and R. K Kimmins. 1985. Reducing
corolla abscission of
Streptocarpus X hybrids under simulated shipping conditions with
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20:118-119.
2. Cameron, Arthur C. and Michael S. Reid. 1983. Use of silver
thiosulfate to prevent flower
abscission from potted plants. Scientia Horticulturae. 19: 373-378.
3. Hammer, A., R. Larson, M. Reid, J. Sacalis, M. Saltreit, and
G. Staby. 1981. How to reduce
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Maximizing Longevity. SAF. October
20-22.
12. Nell, T. A. and J. E. Barrett. 1991. Plan now to eliminate
bract edge burn in your ‘91 poinsettias.
GrowerTalks 54:18-19.
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