What is ethylene?
Ethylene (C2H4) is an odorless, colorless gas that can have both positive and negative impacts on greenhouse crops. It is a plant hormone, which means that it is produced by plants and affects growth and development at very low concentrations. Ethylene plays a role in seed germination, adventitious rooting, fruit ripening, leaf shedding, leaf yellowing and flower death (i.e. senescence). Growers can apply ethylene-based plant growth regulators, like Florel, to increase lateral branching, remove flowers, or prevent flower initiation. Ethylene applications are also used to initiate flowering in bromeliads. Ethylene is often called a stress hormone, because plants produce ethylene in response to stress. This is why you must never apply Florel to plants that are under stress from high temperatures, water deficits, or disease or insect pressures. These plants are already producing elevated levels of ethylene, and a normal Florel application will result in toxic side effects including accelerated leaf yellowing and senescence.
Sources of ethylene in the greenhouse:
Ethylene gas may be produced by both biological (i.e. plants) and non-biological sources. Because it is a gas, ethylene can easily move throughout the greenhouse. The most common source of ethylene contamination in the greenhouse is malfunctioning heating units (Figure 2). Incomplete combustion of organic fuels can result in the production of carbon monoxide, ethylene and other byproducts. CO2 burners used for CO2 enrichment can also produce ethylene. Ethylene from heaters, CO2 burners or any combustion engines can accumulate to damaging (i.e. biologically active) concentrations in greenhouses, especially in tight structures and during the winter months when there is little ventilation. Any equipment including blowers, trimmers, and carts that use combustion engines should therefore be avoided in a production environment. Water heaters used to heat irrigation water should not be located in the production or propagation areas. Leaky gas lines can also result in plant damage in the greenhouse. Both propane and natural gas may contain small hydrocarbon contaminants that can cause ethylene like damage. Burning cigarettes also produce ethylene, so smoking should never be allowed in the greenhouse or near air intakes.
Plants themselves produce ethylene gas that is released into the greenhouse environment. Old or dying (i.e. senescing) flowers and ripening fruit produce more ethylene than leaves and young plants. When plants are wounded due to sleeving, mechanical, or insect damage, they also produce elevated levels of ethylene. Dead plant material that is decaying gives off ethylene. Proper greenhouse sanitation is not just important for preventing disease and insect problems, but it plays an important role in reducing ethylene damage as well. For example, damage to individual plants can occur when dying petals that have fallen from hanging baskets accumulate and decay on the plug trays or young plants below.
Dr. Michelle L. Jones
D.C. Kiplinger Chair in Floriculture
The Ohio State University
Department of Horticulture and Crop Science