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Ethylene in the Greenhouse:
What does ethylene damage look like?
A plant's response to ethylene can vary with temperature, ethylene concentration and duration of exposure. Plant responses to acute or high concentration (> 0.1 ppm), exposures are well described and studied. Many growers can readily identify these symptoms. Brief exposures may occur due to events such as shipping plants in a tightly sealed container or one-time exposure to vehicle exhaust while plants are in a loading zone. Short duration exposures at high concentrations result in flower and leaf abscission, chlorosis, and downward bent leaves that look wilted, but are turgid (epinasty) (Figure 1). Longer-term exposure to high concentrations of ethylene can result in stunted growth, deformed or chlorotic leaves, delayed flowering and plant death (senescence).
However, it can be more difficult to recognize plant responses to low concentration (< 0.05 ppm) exposures. Low concentration exposure to ethylene over extended periods of time (referred to as chronic ethylene exposure) can occur during greenhouse production such as when a furnace is malfunctioning and generates ethylene inside the greenhouse. To develop a visual diagnostic guide of chronic ethylene exposure, an experiment was conducted at Cornell University. Thirty species of bedding and potted plants were grown in separate greenhouses and were exposed to ethylene concentrations of 0.00, 0.01 and 0.05 ppm ethylene every night for the last 6 weeks of production. Some results of these experiments are presented below.
For many plant species responses to low concentration ethylene exposures are subtle and can be easily missed. For example, petunias exposed to 0.01 ppm ethylene for 24 hours, exhibit early senescence of pollen shedding flowers (Figure 2). Of course, as a grower you're not tracking the life span of individual flowers, but the effect in the greenhouse would be a noticeable and sudden loss of petunia flowers in one part of the greenhouse, typically close to a furnace. Similarly zonal geraniums exhibit stipule yellowing after 48 hours when exposed to 0.01 ppm ethylene for 24 hours (Figure 4), yet the flowers do not shatter as is seen at higher concentrations. Longer term exposures at these concentrations result in less flowering for begonia, impatiens and lobelia (Figure 7), and petunia internode elongation and flower size is reduced (Figure 2). The figures below illustrate plant responses to low concentrations of ethylene. Complete results are summarized in Table 1.
If you suspect ethylene is present, then the first thing to do is
verify that there is indeed a problem. One of the easiest ways of
detecting ethylene is by the use of indicator plants. These are plants
so sensitive that they respond dramatically even at concentrations
as low as 0.01 ppm. Cuphea and Tomato both make excellent indicator
plants. Cuphea will abscise all its flowers (Figure 2); and tomato
will bend its leaves downward as if they are wilted but they will
remain turgid (epinasty) when ethylene is present even in very low
concentrations. Such responses usually show up within 24 hours of
exposure, though lower greenhouse temperatures can slow the response.
Use indicator plants which have not previously been exposed to ethylene
and place them throughout the greenhouse including any areas where
you suspect ethylene is originating.
A second and more reliable method to detect ethylene is by sending
an air sample to a commercial lab or a university lab such as the
one at North Carolina State University Plant Disease and Insect Clinic.
Contact the lab directly to find out about the details of the program,
obtain the necessary instructions and materials for collecting an
air sample before sending one in. When taking samples to send for
testing, choose from areas where you suspect ethylene may be coming.
These could be inside, near a unit heater, or outside of the greenhouse,
near a loading dock. Also sample areas where there is no ethylene
problem, as a basis for comparison. Commercial kits for detecting
ethylene are also available, but are not sensitive enough to detect
If you find that ethylene is present in your greenhouse, the next step is to find the source. Ethylene can come from several sources, such as ripening fruit, decomposing plant material, plant growth regulators that release ethylene, and as a by-product of incomplete combustion.
If you discover that you do have an ethylene problem, the easiest and most immediate intervention is periodic ventilation of the greenhouse with clean outside air. Of course this is only a short term fix, and shouldn’t be considered a long term solution, particularly when heating costs are high.
North Carolina State University Plant Disease and Insect Clinic - The clinic offers ethylene testing at very low cost. You will need to contact the clinic directly to obtain details about the program, an ethylene sampling kit, and instructions on how to collect samples.
Heating Systems Maintenance Pays – A general guide to seasonal heating system maintenance for both oil and gas systems.
Avoiding Ethylene Problems. Runkle & Beudry. GPN 2006. Description of common ethylene problems, sources and sampling technique.
Acknowledgements:This work was funded, in part, by a grant from the Fred C. Gloeckner Foundation, Inc. Plant material was donated by C. Raker and Sons, Inc. We also acknowledge the valuable cooperation of numerous New York growers for sharing their insights on their own ethylene experiences.
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© 2007 Department of Horticulture, College of Agriculture and Life Sciences, Cornell University