Leaf Yellowing in Easter Lilies: Causes and Solutions 1995 Proposal
3)
1. Executive 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.
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 continue investigations
of these, problems and find solutions to them. This project has been funded
by the American Floral Endowment for the past two years, and we are requesting
the third year of funding. Thus far, we have conducted numerous experiments
to learn the environmental and cultural factors contributing to each kind
of leaf yellowing including: fertilization and growth regulators (A-Rest,
Sumagic, and gibberellic acid), root rot control, irrigation regime, negative
DIF, and lights in post-harvest (puffy bud) cold storage. 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
also reduce plant carbohydrate levels. Further, lower leaves contain less
nitrogen than upper leaves, and this may be exacerbated by negative DIF.
This linkage of catastrophic leaf yellowing to leaf nitrogen depletion
and to strong negative DIF forcing is the focus of our work for the upcoming
year.
2. Introduction and Literature Review
Easter lilies rank fourth in total value in U.S. floriculture pot crops,
with a reported wholesale value of $35.2 million in 1992 (USDA, 1993).
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,
($5.22 vs. $2.50), and only African violet is more valuable on a square
foot basis than lilies (USDA, 1993).
Easter lilies, however, suffer from two potentially serious leaf-yellowing
disorders. Miller (1991) identified the “gradual” and “catastrophic” syndromes
described above, and has identified lack of keeping quality as one of the
greatest problems facing lily forcers. Gradual lower leaf yellowing usually
starts after flower initiation in late January. The problem appears to
be mainly due to plant stress resulting from low nitrogen or phosphorus,
and interactions with growth regulator drenches.
A-Rest, Bonzi, and Sumagic are closely linked to gradual leaf yellowing
(Tsujita et al., 1978; 1979, Jiao et al., 1986, W. B. Miller and D. A.
Bailey, unpublished data), especially when applied as drenches. It has
been proposed that growth regulators may cause leaf senescence by inducing
sugar and nutrient export to developing buds (Jiao et al., 1986) which
are the major carbohydrate “sink” during the last 6 weeks of development
(Miller and Langhans, 1989 a,b).
Gradual leaf yellowing apparently can be reduced by top-dressing with
slow release nitrogen fertilizers (Miller, 1991), and there are indications
that low phosphorus nutrition exacerbates the problem (Tsujita et al.,
1978; 1979). Eliminating liquid fertilizer 4-6 weeks before shipping increases
leaf yellowing (Prince and Cunningham, 1989). Ethylene does not appear
to be involved in leaf yellowing, but bud blast (another storage-related
disorder), is reduced by anti- ethylene compounds (Prince et al., 1987;
Mason and Miller, 1991). Additional work on interactions of ethylene and
temperature stress are needed, however. Gradual leaf yellowing may also
be linked to reduced leaf carbohydrate levels. A-Rest, Bonzi, and Sumagic
treatments can reduce leaf carbohydrates in lilies (Jiao et al., 1986;
Bailey and Miller, 1989). Lilies grown with negative DIF are known to develop
chlorotic: leaves in the greenhouse (Heins, 1990). Negative DIFs of -9
or -14′F caused a loss of 45% of leaf and stem carbohydrate in ‘Nellie
White’, (Miller et al., 1993). Finally, because growth-regulator-treated
and negative DIF plants have reduced leaf area, transpiration and water
demands, there is a tendency to over-water them.
The second form of leaf yellowing has been termed “catastrophic yellowing”,
and shows up 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. While symptoms develop during the post-harvest
phase, catastrophic leaf yellowing is not strictly a “post- production
problem”, as cultural factors (A-Rest application, low phosphorous, poor
root rot control, negative DIF, cold storage and warm shipping) all interact
to influence symptom severity during shipping and marketing.
Although storing early plants up to 3 weeks is long-standing commercial
practice (Staby and Erwin, 1977; Wilkins, 1980), length of cold storage
after forcing is clearly correlated with percentage leaf yellowing (Prince
et al, 1987). Lengthy cold storage followed by a (potentially) warm 1 to
4 day shipping period imposes an enormous stress on the plant. Prince (1990)
reported that failure to rigorously control the root rot complex was associated
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 loss in lily plants
during cold storage, and found that lily leaves lost nearly as much carbohydrate
in 2 or 3 weeks of 40′F (4′C) cold storage as in 6 days of 70′F (21′C)
dark simulated shipping.
In many species, leaf senescence and chlorophyll degradation can be
reduced or eliminated altogether by foliar sprays of cytokinins or gibberellins
(Thimann, 1980). Alstroemeria (a member of the lily family) suffers a serious
leaf-yellowing problem, and gibberellin or cytokinin pulses to cut stems
effectively reduce leaf yellowing (Hicklenton, 1991; van Doorn et al.,
1992). Gibberellin sprays 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).
3. Objectives and Anticipated Benefits
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, disseminated
through trade literature, and other methods, for the industry.
Anticipated Benefits: We are evaluating the cultural factors
(growth regulators, nutrition, fungicide application, high temperature
forcing, negative DIF, shipping, and cold storage) which are involved in
two leaf yellowing disorders in Easter lilies. Our research is of great
value to the industry for maintaining profitability of the crop for the
forcer and retailer. This research will eventually allow confident growing,
handling and shipping of this crop and reduce economic loss in the industry.
4. Materials and Methods
During the last two forcing seasons (1993 and 1994), we have conducted
many experiments at Purdue and Clemson to determine the main factors contributing
to these leaf yellowing problems. Selected specific actions relating to
this work, and future work plans are given below. Partial funding (less
than half of budget request) in 1994 slowed progress somewhat, but we are
still excited by the progress we have made. Since the inception of this
project, we have gained good experience in coordinating a research program
between two universities. We have found that electronic mail and, perhaps
somewhat surprisingly, in-person contact are both essential for good research
progress. We have effectively used e-mail for the last two years to rough-out
experimental plans and for communicating between Clemson and Purdue. In-person
contact was very valuable when W. B. Miller traveled to Indiana in March
1993. Drs. Miller and Hammer worked on project planning and also visited
more than 10 lily forcers and saw over 300,000 lilies. When visiting growers,
we mentioned the Endowment as a source of our research funding. This trip
clearly pointed out the fact that gradual leaf yellowing can occur under
a range of conditions, fertilizer and temperature regimes, soil types,
etc.
At Clemson, Mr. Anil P. Ranwala has been working on this project to
fulfill requirements for his Ph.D. assistantship. Anil is a highly qualified
and motivated individual. A native of Sri Lanka, he conducted his Master’s
research in Japan and is fluent in Japanese. He came to Clemson in May,
1992 and has been involved with this project from its inception. He will
be presenting results of this research in Corvallis, Oregon, at the annual
American Society for Horticultural Science meetings in August, 1994.
The following hypotheses are now offered, 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, perhaps caused by the induction
of bulb scale filling during cold storage.
Action: In 1993, plants were grown to testing this hypothesis.
In 1993-94, we collected leaf samples from lower, middle, and upper regions
of the canopy and analyzed for nitrogen. We found lower leaves averaged
about 1.5% N, whereas upper leaves had about 3.9% N. Clearly, nitrogen
deficiency is a factor in lower leaf yellowing, and supports commercial
observations. In lighting studies in cold storage, plants were exposed
to approximately 250-300 foot-candles fluorescent light during 40′F cold
storage. Light greatly increased leaf carbohydrate level, and had a positive
effect on flower life, and a smaller, but still positive effect on positive
effect on foliage quality.
Hypothesis: Negative DIF, or high forcing temperatures, by reducing
plant carbohydrate, or influencing nitrogen partitioning, increase the
incidence of post-harvest leaf yellowing.
Action: We have already shown that negative DIF reduces lily
carbohydrate levels, probably by increasing night respiration levels (Miller
et al., 1993). The question now arose: Is negative DIF related to leaf
yellowing? In 1993, plants were grown at Purdue under a positive or negative
DIF (approximately +9 or -9′F). At harvest, plants were sleeved, boxed,
and shipped by UPS to Clemson. A similar group of non-shipped (control)
plants were retained at Purdue. All plants were green and healthy upon
arrival in Clemson. After 4 day postharvest, however, more than 50% of
the leaves on the negative DIF plants had turned yellow, with no yellowing
on the positive DIF plants. Over a 2 week post harvest period, the positive
DIF plants also developed chlorosis, but the negative DIF plants were always
much worse than the positive DIF plants. Leaf yellowing was much less severe
in the Purdue plants, suggesting that dark shipping is important in this
problem. Tissue samples were analyzed for carbohydrates and nitrogen. As
expected, the negative DIF plants had much less carbohydrate at the start
of post harvest. After 4 days post harvest, the negative DIF plants had
1.5% N in the lower leaves compared to 2.5% N in the positive DIF controls.
Negative DIF plants had higher upper leaf N, suggesting negative DIF affects
partitioning of nitrogen within the canopy, i.e., negative DIF encourages
loss of lower leaf N, leading to increased lower leaf yellowing. We tentatively
conclude that strong negative DIF temperatures may be related to catastrophic
leaf yellowing. New questions to consider are: What are the limits to the
shipping environment, how long lasting is the negative DIF effect, (can
it be reversed by growing at 0 or positive DIF, or with a morning temperature
drop?), and how should fertilizer schemes be altered to compensate for
altered N distribution?
Hypothesis: Application of cytokinin or gibberellin will reduce
catastrophic leaf yellowing.
Action: In 1994, we conducted two experiments to investigate
possible effects of gibberellic acid in reversing or eliminating catastrophic
leaf yellowing. Pro-Gibb (1,000 ppm) was applied to plants (with or without
earlier A-Rest drenches) at the puffy bud stage and just prior to placement
in the cooler. Positive effects were seen from the Pro-Gibb, in non-cold
stored, A-Rest drenched plants. Gibberellin was not beneficial in cold-stored
plants. Importantly, the Pro-Gibb treatments did not cause any upper plant
stretch whatsoever, and individual flower longevity was improved by a full
day over non-GA treated plants. We plan additional experiments to expand
and confirm these findings in 1994-1995. Various levels of cytokinins (N6-benzyladenine,
zeatin, zeatin riboside, kinetin), and gibberellins (gibberellic acid,
gibberellin A4+7) will be sprayed and/or drenched to test efficacy against
leaf yellowing. Action: planned for 1994-1995.
Hypothesis: Root rot control is essential for successful storability.
Action: Isolations from roots of symptomatic and non-symptomatic
plants have been conducted to determine the presence of root rot organisms.
In 1993, root isolations on selective media indicated Pythium- like organisms
on all plants grown at Purdue and Clemson, even those not showing excessive
leaf yellowing. Difficulty in accurately quantifying pathogen populations
in media have caused us to focus on other factors rather than pathogens
per se.
Hypothesis: Catastrophic leaf yellowing (ie. chlorophyll degradation)
in cool-stored lilies is dependent on post-harvest light and/or temperature.
Action: planned for 1994-1995. Other: We are now working on
a series of articles for the trade press that will highlight our findings
to date and suggest some “best management practices” to lessen the chance
of leaf yellowing in the 1995 lily crop. Certainly, the American Floral
Endowment will be acknowledged in these publications. A nice story is emerging
that implicates nitrogen nutrition, negative DIF forcing, and post-harvest
handling in a complex interaction that influences catastrophic leaf yellowing.
The linkage of catastrophic leaf yellowing to leaf nitrogen depletion and
strong negative DIF forcing is the focus of our work for the upcoming year.
Publications/presentations arising from this work:
Miller, W. B., P. A. Hammer, and T. I. Kirk. 1993. Reversed greenhouse
temperatures reduce carbohydrate status in Lilium longiflorum Thunb. ‘Nellie
White’. J. Amer. Soc. Hort. Sci. 118:736-740.
Whipker, B. E., T. Kirk, W. B. Miller, and P. A. Hammer. 1994. Nutrient
partitioning in ‘Nellie White’ Easter lilies grown under two temperature
regimes. HortScience 29:542. (abstract).
Ranwala, A. P., W. B. Miller, P. A. Hammer, and T. Kirk. 1994. Causes
of postharvest leaf yellowing in Easter lilies. HortScience 29:554. (abstract).
Miller, W. B. 1994. Relationship of carbohydrate to potted plant senescence.
(Invited workshop presentation at 1994 ASHS meetings, Corvallis, OR). HortScience
29:391.
Whipker, B. E., P. A. Hammer and W. B. Miller. 199x. Nutrient partitioning
in’Nellie White’ Easter lilies at anthesis when grown under two temperature
regimes. HortScience (submitted for publication).
Ranwala, A. P., W. B. Miller, P. A. Hammer, and T. I. Kirk. Leaf yellowing
in Easter lilies. (in preparation). Presentation of leaf yellowing research
to industry audiences: South Carolina Greenhouse Grower’s Association.
Winter meetings 1993, 1994. Southeast Greenhouse Conference and Trade Show,
June 1993. Indiana Flower Growers Meeting, June, 1993.
5. 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. Tayarna, 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.
Rao, 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. O. 1991. Lilies. In: V. Ball (Ed.). Ball RedBook. 15th Ed.
Geo. J. Ball Publ. West Chicago. IL p. 625-651.
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.
Miller, W. B., P. A. Hammer, and T. I. Kirk. 1993. Reversed greenhouse
temperatures reduce carbohydrate status in Lilium longiflorum Thunb. ‘Nellie
White’. J. Amer. Soc. Hort. Sci. 118:736-740.
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. 1993. Floriculture Crops. 1992 Summary. SpCr. 6-1(93). 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.
6. Budget:
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
Actually Funded:
(10,000)
Purdue University Budget
(supplies and operations)
3,000 3,700
4,400 11,100
Actually Funded:
(2,000)
Yearly Totals; both institutions 22,000
26,200 30,400
78,600
Actually Funded:
(12,000)
Plant material and other donations will be solicited from industry when
appropriate. We will likely request an nonfunded extension of the project
for the 1996 forcing season.
7. Project Personnel Qualifications:
William B. Miller has conducted research with Easter lilies
for 10 years, and has published numerous scientific papers on lily physiology
and carbohydrate metabolism. His book, Easter and Hybrid Lily Production,
was published by Timber Press in 1992. Miller wrote the chapter on Lilium
longiflorum in the book, Physiology of Flower Bulbs and has presented invited
lectures on his bulb research at the Bulb Research Center in Holland. Since
1983, his lily research has been supported by the American Floral Endowment,
the Fred C. Gloeckner Foundation, the Easter Lily Research Foundation,
and Dahlstrom and Watt Bulb Farms, Inc. P.
Allen Hammer is Professor of Floriculture at Purdue University.
His 20-plus years of research at Purdue have included most of the economically
important floriculture crops. His area of focus is 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 provides close
ties with industry, providing the link between laboratory and commercial
greenhouses.
Nihal C. Rajapakse has conducted research on post-harvest physiology
of floricultural and other horticulture crops for more than 10 years. His
research interests include 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.
James H. Blake has worked in the area of ornamentals disease
diagnosis over 12 years. He 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.
