Date September 1, 1993

Title of Project Leaf Yellowing in Easter Lilies: Causes and Solutions

Institution where work is being conducted Clemson University and Purdue University

Amount of Endowment Grant $ 22,000
Covering Period 1/93 to 12/93

Anticipated Date of Project Completion/Final Report Dec. 1995 or Dec. 1996

Individual(s) Conducting Project:

(List Project Leader First)

Dr. William B. Miller, Project Leader - Title Associate Professor

Telephone Number 803-656-0898

Dr. P. Allen Hammer - Title Professor

Dr. Nihal C. Rajapakse - Research Associate

Mr. James H. Blake - Title Extension Associate

Leaf Yellowing in Easter Lilies: Causes and Solutions

William B. Miller, P. Allen Hammer, Nihal C. Rajapakse, James H. Blake

Clemson University and Purdue University

Progress Report to the American Floral Endowment, 9/1/93

A. Project Objectives:

1. Define and systematically study cultural practices that influence gradual (greenhouse) and

catastrophic (postharvest) leaf yellowing in Easter lily.

2. Evaluate potential remedial practices, including anti-senescence chemical treatments.

3. Develop cultural and/or other production guidelines, disseminated through trade literature

and other sources, for the industry.

B & C. Summary and Results of Work Completed to Date:

Mr. Anil Ranwala, a Ph.D. candidate at Clemson, is assisting in the research and is doing a

very effective job with the project. Since the spring crop, he has analyzed more than 300

carbohydrate samples, with more than 500 to go.

In general, we had trouble inducing greenhouse (gradual) leaf yellowing in Clemson. We

have a high fertility program, with 300 ppm N applied at each watering. (We alternate 20-10-20

with calcium nitrate plus potassium nitrate). Our climate is relatively warm, and we grow in

highly ventilated, glass greenhouses. The plants tend to dry quickly, favoring good root health.

We applied standard drenches for root rot, including two Subdue applications, and still isolated

Pythium from nearly every plant we grew. It is important to realize that Pythium will be more of a

problem in stressed and over watered plants as it is a water-loving fungus.

This past spring, we held Clemson-grown puffy bud lilies at 40-45′F for up to 3 weeks, with

or without fluorescent lights. In some experiments, plants were placed directly into the post

harvest room, in other cases, plants were sleeved and held in the dark at 86′F or 68′F for two days to

simulate shipping. Simulated shipping at 86′F caused 5-10% more leaf yellowing than at 68′F, and

also reduced flower life by about 1 day. Lights in the cooler increased flower life by a full day

over plants held without lights, and reduced bud abortion by 50%. A late application of nitroform.

very slightly increased leaf chlorophyll levels at flowering.

To test the hypothesis that negative DIF increases post-harvest leaf yellowing, plants were

grown at Purdue with positive or negative DIF’s (¬± 10 F) to give equal 24-hour temperature

averages. Plants were shipped to Clemson by UPS and observed under post harvest conditions.

There was no effect of negative DIF on flower longevity, but negative DIF increased by 6-fold the

number of aborted flower buds. Negative DIF reduced leaf carbohydrate level, and significantly

increased post-harvest leaf yellowing. For example, after 6 days in the postharvest room, negative

DIF plants had 3 times more yellowed lower leaves compared to positive DIF controls (36% vs.

12%). Lower leaves had much less carbohydrate than upper leaves at any time during the post

harvest period. Further, leaf yellowing was negatively correlated to leaf sucrose level. These

results indicate that temperature stresses which reduce leaf carbohydrate levels contribute to post

harvest leaf yellowing, and large negative DIF’s and otherwise excessive temperatures should be

avoided, if possible. More detailed information is available from Bill Miller, 803-656-0898.

D. Future Plans Covered by the Endowment Grant:

We are continuing to analyze tissue samples from this past spring, and will be conducting nitrogen

analysis this fall. We have ordered bulbs for the 1994 season, and will be repeating several of this

year’s experiments, and starting new ones, such as application of several chemicals which may

reduce the yellowing problem. A trade journal article is being written with our results thus far.

E. Anticipated Benefits for Floral Industry:

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: 1) a gradual yellowing of basal

leaves during forcing, and 2) “catastrophic yellowing” which 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. We are evaluating the cultural factors

(growth regulators, nutrition, fungicide application, high temperature forcing, shipping, and cold

storage) which are involved in these disorders. Our research is of great value to the industry for

maintaining profitability of the crop. If successful, it would allow confident handling and shipping

of this crop and reduce economic loss in the industry.

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