Leaf Yellowing in Easter Lilies: Causes and Solutions 1993 Proposal
A. Summary
While Easter lilies are among the most valuable crops on a square foot
basis in U. S.
floriculture, they suffer from two potentially serious leaf-yellowing disorders.
The most
common is a gradual yellowing of basal leaves during forcing. The problem
appears to
be mainly due to nitrogen deficiency and is usually prevented by topdressing
a dry slow-
release nitrogen fertilizer.
The second and more disastrous form of leaf yellowing is termed “catastrophic
yellowing”, and mainly occurs during post-production shipping and marketing.
This
disorder strikes quickly, causing a normal looking plant to turn almost
entirely yellow
within a few days after cold storage. Cultural factors (growth regulators,
low
phosphorus, poor root rot control, high temperature forcing, shipping delays
and cold
storage) appear to be the major causes. Our work indicates lily plants
lose much of their
carbohydrate reserves during post-production cold storage and warm shipping,
and that
negative DIF and growth regulators can also reduce plant carbohydrate levels.
Thus,
specific production stresses, combined with reserve-depleting cool storage
and/or warm
shipping are hypothesized to lead to “catastrophic” leaf yellowing.
We propose, through our interdisciplinary team, to investigate these problems
and
find solutions to them. Experiments in gradual leaf yellowing will be conducted
to assess
leaf nitrogen status during growth as influenced by a variety of fertilization
and growth
regulator regimes. Experiments in catastrophic yellowing initially define
conditions
under which this disorder occurs. Factors to evaluate include: A-Rest and
Sumagic, root
rot control, forcing temperature in the last weeks of production, irrigation
regime,
negative DIF, etc. With the aid of our plant pathology collaborator, we
will isolate
organisms from roots of symptomatic and non-symptomatic plants to determine
the
nature of root rot organisms. Multiple-year funding is necessary for this
project due to
the nature of the crop (one production season/year) and the complexity
of the problem.
B. Detailed Proposal
1. Introduction
Easter lilies rank fourth in total value in U.S. floriculture pot crops,
with a reported
wholesale value of $36.9 million in 1990 (USDA, 1991). On a per-area basis,
the crop is
exceptionally profitable. For example, the crop has more than twice the
value per square
foot than poinsettia, ($5.14 vs. $2.50), and only African violet is more
valuable on a
square foot basis than lilies (USDA, 1990). The crop is produced throughout
the U.S.
and marketed for Easter sales.
While Easter lilies are one of the highest return crops on a square foot
basis in
U.S. floriculture, the crop suffers from two potentially serious leaf-yellowing
disorders.
The first is a gradual yellowing of basal leaves during, usually starting
after flower
initiation in late January. The problem appears to be mainly due to plant
stress resulting
from low phosphorus, low nitrogen, and an interaction with growth regulator
drenching
The second form of leaf yellowing has been termed “catastrophic yellowing”,
and
mainly occurs during post-production shipping and marketing. This disorder
strikes
quickly, causing a normal looking plant to turn almost entirely yellow
within a couple of
days, and is exacerbated by cold-storing, plants before shipping. Especially
in late-Easter
years, plants are often cold-stored at the “puffy bud” stage for up to
3 weeks, followed by
a 1 to 4 day shipping period, which is often not temperature-controlled.
The stresses
placed on the plant from this handling are enormous. Leaf yellowing is
not, however,
strictly a post-production problem, as cultural factors (A-Rest application,
low
phosphorous, poor root rot control) all interact to influence the severity
of the problem.
Since this is a complex disorder, a systematic approach is needed to define
and solve the
problem.
2. Literature Review
Surprisingly little work has been conducted on leaf yellowing in Easter
lilies. Miller
(1991) has separated the disorder into the “gradual” and “catastrophic”
types described
above, and has highlighted the potential lack of keeping quality as one
of the greatest
problems facing lily forcers. The P.I. (Miller, 1992 a,b) reviewed research
conducted on
“gradual” leaf yellowing, which is summarized below.
Length of cold storage after forcing is clearly correlated with percentage
leaf
yellowing (Prince et al, 1987). Leaf yellowing in general is caused by
chlorophyll
degradation, which itself has many causes within plants. In a wide range
of species, leaf
senescence and chlorophyll degradation can be reduced or eliminated altogether
by foliar
sprays of cytokinins of gibberellins (Thimann, 1980). Indeed, Alstroemeria
(a member of
the lily family) suffers a serious leaf-yellowing problem, and gibberellin
or cytokinin
pulses effectively reduce leaf yellowing (Hicklenton, 1991; van Doorn et
al., 1992).
Gibberellin enhanced individual flower longevity of lilies, but data on
leaf yellowing
were not collected (Kelley and Schlamp, 1964). Cytokinin sprays had little
effect on
stored lilies, but too low of a concentration may have been used (Healy
et al., 1979).
A-Rest drenches are closely linked to gradual leaf yellowing (Tstijita
et al., 1978;
1979). Bonzi drenches, while not economically effective as a lily height
control
treatment, also cause lower leaf yellowing (Jiao et al., 1986). It has
been proposed that
growth regulators may cause leaf senescence by inducing sugar and nutrient
export to
developing buds (Jiao et al., 1986). Developing buds are indeed the main
carbohydrate
sink” during the last 6 weeks of development (Miller and Langhans, 1989
a,b).
Sumagic, a close relative to Bonzi, and a powerful lily height regulator,
also cause the
disorder (W. B. Miller and D. A. Bailey, unpublished data).
There are indications that low phosphorus nutrition encourages gradual
leaf
yellowing (Tsujita et al., 1978; 1979), and topdressing with a slow release
nitrogen
fertilizer is an effective preventative measure (Miller, 1991). Eliminating
liquid fertilizer
4-6 weeks before shipping increased leaf yellowing (Prince and Cunningham,
1989).
Ethylene does not appear to be involved in leaf yellowing, but bud blast
(another storage-
related disorder), and can be reduced by anti-ethylene materials (Prince
et al., 1987;
Mason and Miller, 1991). Additional work on ethylene and leaf yellowing
is needed,
however.
Gradual leaf yellowing may also be linked to reduced leaf carbohydrate
levels. A-
Rest, Bonzi, and Sumagic treatments reduce leaf carbohydrates in ‘Nellie
White’ lilies
(Jiao et al., 1986; Bailey and Miller, 1989). These reductions could be
from direct
growth regulator effects, or from induced mutual leaf shading caused by
reduced
internode length of treated plants. Plants grown with negative DIF are
known to develop
chlorotic leaves (Heins, 1990). Negative DIFs of -9 or – 14 F caused a
loss of 45% of leaf
and stem carbohydrate in ‘Nellie White’, in 2 years of trials (Miller et
al., in review).
Because growth-regulator-treated and negative DEF plants have reduced leaf
area, and
thus reduced transpiration and water demands, there is a tendency to over-water
them.
This situation could weaken roots and lead to attack by root rot pathogens.
Catastrophic leaf yellowing has received even less attention, but the disorder
is
definitely associated with cold storage of early plants. Storing early
plants up to 3 weeks
is long-standing commercial practice (Staby and Erwin, 1977; Wilkins, 1980).
Prince
(1990) reported that failure to rigorously control the root rot complex
was ssociated with
catastrophic leaf yellowing. Plants with 20-30% visibly infected roots
had 5 times more
chlorotic leaves after 12 days in an interior environment than controls.
Miller (1992a)
investigated carbohydrate reserve loss in lily plants during cold storage,
and found that
lily leaves lost nearly as much carbohydrate in 2 or 3 weeks of 4OF (4C)
cold storage as
lost in 6 days of 7OF (21C) dark simulated shipping.
3. Objectives
A. Define and systematically study cultural practices that influence leaf
yellowing (both
gradual and catastrophic) in Easter lily.
B. Evaluate potential remedial practices, including anti-senescence chemical
treatments.
C. Develop cultural and/or other production guidelines, dessiminated. through
trade
literature and other sources, for the industry.
4. Materials and Methods
Initially, experiments will be conducted to determine the main factors
contributing to the
problem. Since lilies are a once-per-year crop, careful planning is essential
for efficient
research,progress. All studies involving catastrophic yellowing will include
a 2-3 week
storage period, followed by a 2-6 day warm (70F or more) simulated shipping
period.
Storage factors include: cultivar, storage temperature, presence of light,
etc. Preliminary
studies and communication with industry leaders who have experienced this
problem will
help determine these “standard” conditions.
The following hypotheses are offered initially, and do not exclude the
development of other hypotheses and ideas as the research progresses:
Hypothesis: Post-storage catastrophic leaf yellowing is due to leaf nitrogen
and/or
carbohydrate depletion caused by the induction of bulb scalefilling during
cold storage.
Leaves (lower, middle, upper) will be sampled during the storage period
and analyzed for
protein, nitrogen and carbohydrate to assess the extent of nitrogen and
carbon loss. This
sampling will be continued into the post-harvest evaluation phase. Sucrose
sprays to
replenish leaf carbohydrates lost in storage will be attempted.
Hypothesis: Catastrophic leaf yellowing (i.e. chlorophyll degradation)
in cool-stored
lilies is dependent on postharvest light and/or temperature. Previously
stored plants will
be held at 70, 60, or 50 F, with or without “typical” room lighting. Onset
of leaf
yellowing will be followed over time, and leaves sampled for chlorophyll
loss.
Hypothesis. Negative DIF, or highforcing temperatures, by reducing plant
carbohydrate, increase the incidence of post-harvest leaf yellowing. Plants
will be grown
with a positive or negative DIF (eg. +9 or -9 F), or at elevated finishing
temperatures at
both Purdue and Clemson. Leaf senescence will be evaluated at flowering,
and after
interior post-harvest evaluation. Leaf samples will be collected for carbohydrate
and
nitrogen analysis. After sample collection, Purdue-grown plants will be
shipped to
Clemson for post-harvest evaluation.
Hypothesis: Catastrophic
leafyellowing is related to ethylene. This will be tested by
applying various concentrations of ethylene action or synthesis inhibitors
(STS, AOA,
norbornadiene) to plants prior to and/or after storage, then evaluating
after a standard
post-harvest period. Potential of soil surface fungi to produce physiologically-
detrimental ethylene will be assessed.
Hypothesis: Application of cytokinin or gibberellin will reduce catastrophic
leaf
yellowing. Various levels of cytokinins (N^6-benzyladenine, zeatin, zeatin
riboside,
kinetin), and gibberellins (gibberellic acid, gibberellin A3) will be sprayed
and/or
drenched to test efficacy against leaf yellowing.
Hypothesis. Root rot control is essentialfor successful storability. A
combination of
preventative drenches will be witheld at various times during forcing,
and effects on
catastrophic leaf yellowing will be determined under standard conditions.
Isolations from
roots of symptomatic and non-symptomatic plants will be conducted to determine
the
presence of root rot organisms.
5. Facilities and Equipment Available
At Clemson University, the P.I.’s have more than 1,600 sq. ft. of assigned
laboratory space which is exceptionally well-equipped for floriculture
and post-harvest
physiology research. Approximately 300 square feet of newly constructed
post-harvest
evaluation space will be available to support the project. This room has
temperature,
irradiance, and humidity control and monitoring. The P.I.s together have
about 3,000
square feet of greenhouse space available for the project, within 200 yards
of the labs.
Co-P.I. Blake is director of a 1,300 sq. ft. diagnostic laboratory with
all essential
equipment for the pathology work disease diagnosis is available at Clemson.
Facilities at
Purdue are more than adequate for the proposed research.
Major laboratory equipment available to the project (housed in Miller’s
or
Rajapakse’s labs): HPLC #1: An isocratic system dedicated to carbohydratework;
HPLC
#2: Waters system for general use with an autosampler; HPLC #3: includes
a Dionex
pulsed electrochemical detector (100-fold more sensitive than refractive
index for
carbohydrate work).; 4 temperature-controlled incubators; glass still and
water collection
system; 2 gas chromatographs (with FED and TCD detectors); UV-VIS
spectrophotometer; reach-in chromatography refrigerator with a low pressure
protein
chromatography system; 8′ wide fume hood; lab ovens; freeze driers; liquid
nitrogen
supply and storage; portable photosynthesis equipment; porometers; computers;
ultra-low
freezer; water baths; all types of centrifuge equipment, solvent evaporators;
ice machine;
adjustable and fixed volume pipets; polytron with 3 heads; fraction collectors;
misc.
equipment (balances, pH meter, vortexers, stir plates, hot plates, glassware
etc.).
6. Literature Cited
Bailey, D. A. and W. B. Miller. 1989. Whole-plant response of Easter lilies
to ancymidol
and uniconazole. J. Amer. Soc. Hort. Sci. 114:393-396.
Healy, W. E., R. D. Heins, and H. F. Wilkins. 1979. Short-term storage
of Lilium
longiflorum Thunbergia in the “puffy” flower bud stage of development.
Flor. Rev.
163(4231):21.
Heins, R. D. 1990. Temperature and photoperiod. In: R. A. Larson, H. K.
Tayama, and
T. J. Roll (eds.). Tips on Growing Potted Easter Lilies. Ohio State Univ.
Hicklenton, P. R. 1991. GA3 and benzylaminopurine delay leaf yellowing
in cut
Alstroemeria stems. HortScience 26:1198-1199.
Jiao, J., M. J. Tsujita, and D. P. Murr. 1986. Effects of paclobutrazol
and A-Rest on
growth, flowering, leaf carbohydrate, and leaf senescence in ‘Nellie White’
Easter lily
(Lilium longiflorum Thunb). Scientia Hortic. 30:135-141.
Kelly, J. D. and A. L. Schlamp. 1964. Keeping quality, flower size and
flowering
response of three varieties of Easter lilies to gibberellic acid. Proc.
Amer. Soc. Hort.
Sci. 85:631-634.
Mason, M. R. and W. B. Miller. 1991. Flower bud blast in Easter lily is
induced by
ethephon and inhibited by silver thiosulfate. HortScience 26:1165-1167.
Miller, R. 0. 1991. Lilies. In: V. Ball (Ed.). Ball RedBook. 15th Ed. Geo.
J. Ball Publ.
West Chicago. IL p. 625-651.
Miller, W. B., P. A. Hammer, and T. I. Kirk. 199_. Reversed greenhouse
temperatures
reduce carbohydrate status in Lilium longiflorum Thunb. ‘Nellie White’.
J. Amer.
Soc. Hort. Sci. (in review).
Miller, W. B. 1992a. Easter and Hybrid Lily Production. Timber Press. Portland,
Oregon, U.S.A. ISBN 088192-205-6.
Miller, W. B. 1992b. Lilium longiflorum. In: A. A. De Hertogh and M. Le
Nard (eds.).
The Physiology of Flower Bulbs. Elsevier. Amsterdam. (in press).
Miller, W. B. and R. W. Langhans. 1989a. Reduced irradiance affects dry
weight
partitioning in Easter lily. J. Amer. Soc. Hort. Sci. 114:306-309.
Miller, W. B. and R. W. Langhans. 1989b. Carbohydrate changes of Easter
lilies during
growth in normal and reduced irradiance environments. J. Amer. Soc. Hort.
Sci.
114:310-315.
Prince, T. A. 1990. Postproduction care and handling. In: R.A. Larson,
H. K. Tayama,
and T. J. Roll, eds. Tips on growing Easter lilies. The Ohio State Univ.
Prince, T. A., and M. S. Cunningham. 1989. Production and storage factors
influencing
quality of potted Easter lilies. HortScience 24:992-994.
Prince, T. A., M. S. Cunningham, and J. S. Peary. 1987. Floral and foliar
quality of
potted Easter lilies after STS or phenidone application, refrigerated storage,
and
simulated shipment. J. Amer. Soc. Hort. Sci. 112:469-473.
Staby, G. L. and T. D. Erwin. 1977. The storage of Easter lilies. Flor.
Rev.
161(4162):38.
Thimann, K. V. 1980. The senescence of leaves. In: K. V. Thimann (ed.).
Senescence in
Plants. CRC Press, Boca Raton, FL.
Tsujita, M. J., D. P. Murr, and A. G. Johnson. 1978. Influence of phosphorus
nutrition
and ancymidol on leaf senescence and growth of Easter lily. Can J. Plant
Sci. 58:287-
290.
Tsujita, M. J., D. P. Murr, and G. Johnson. 1979. Leaf senescence of Easter
lily as
influenced by root/shoot growth, phosphorus nutrition and ancymidol. Can.
J. Plant
Sci. 59:757-761.
USDA. 1991. Floriculture Crops. 1990 Summary. SpCr. 6-1(91).
van Doorn, W. G., J. Hibma, and J. de Wit. 1992. Effect of erogenous hormones
on leaf
yellowing in cut flowering branches of Alstroemeria pelegrina. Plant Growth
Reg.
11:59-62. (corrections to this paper are pending).
Wilkins, H. F. 1980. Easter lilies, p. 327-352. In: R. A. Larson (ed.).
Introduction to
Floriculture. Academic Press, New York, N.Y.
Zieslin, N. and M. J. Tsujita. 1988. Regulation of stem elongation of lilies
by
temperature and the effect of gibberellin. Scientia Hortic. 37:165-169.
7. Clemson University Budget
Year 1 Year 2
Year 3
1/93-12/93 1/94-12/94
1/95-12/95 Total
Ph.D. Assistantship
11,000 12,000
13,000 36,000
Laboratory supplies
3,000 4,000
5,000 12,000
& operations
Greenhouse supplies
3,000 4,000
5,000 12,000
& operations
Pathology supplies
2,000 2,500
3,000 7,500
& operations
Clemson Univ. Yearly Totals
19,000 22,500
26,000 67,500
Purdue University Budget
(supplies and operations)
3,000 3,700
4,400 11,100
Yearly Totals; both institutions 22,000
26,200 30,400
78,600
Plant material and other donations will be solicited from industry when
appropriate.
C. Project Personnel Qualifications:
William B. Miller has conducted research with Easter lilies for 9 years,
and has
published numerous scientific papers on Lilium physiology and carbohydrate
metabolism.
Miller’s major research interests are plant and insect carbohydrate metabolism
and
floriculture crop physiology. His book, Easter and Hybrid Lily Production,
was
published by Timber Press in 1992. Upon invitation by Dr. Gus De Hertogh,
Miller
wrote the chapter on Lilium longiflorum for the soon to be published Physiology
of
Flower Bulbs. He spoke on lilies at the 1991 International Floriculture
Industry Short
Course, and at GrowerExpo’91. He recently presented invited lectures on
bulb and
whitefly carbohydrate metabolism in Holland, Switzerland, and Poland. He
wrote the
“Physiological Disorders” section of Tips on Growing Potted Easter Lilies,
and published
1992 lily schedules in GrowerTalks. Since 1983, his lily research has been
supported by
the Fred C. Gloeckner Foundation, the Easter Lily Research Foundation,
and Dahlstrom
and Watt Bulb Farms, Inc. A major project dealing with sweet potato whitefly
carbohydrates is currently funded by Cotton, Inc.
Nihal C. Rajapakse has conducted research on post-harvest physiology of
floricultural
and other horticulture crops for 10 years publishing 7 papers on floriculture
post-harvest
physiology in this time. His current research interests include the use
of non-chemical
methods for regulating growth of floriculture crops and post-harvest physiology
of
horticulture crops with a special emphasis on controlled/modified atmosphere
storage.
P. Allen Hammer is Professor of Floriculture at Purdue University. His
20 years of
research at Purdue have included most of the economically important floriculture
crops.
his area of focus is in plant growth and development. He has numerous scientific
papers
on plant growth modeling with some work in this area focused on Easter
lilies. His work
in extension has provided close ties with industry which provides a vehicle
to take
research from the laboratory to the commercial greenhouse.
James H. Blake has studied and worked in the area of plant disease diagnosis
over 12
years, concentrating on diseases of ornamentals. He has worked in diagnostic
clinics at
the University of Arkansas and University of Florida and is currently the
Director of the
Clemson University Plant Problem Clinic. He was selected to serve on the
American
Phytopathological Society Diagnostics Committee through 1994. In 1991,
he began
teaching a new course on Diseases of Ornamental Plants.
