Crops grown in greenhouses that use gas fired heating units can be susceptible to ethylene injury. Ethylene (C2H4) is odorless, colorless gas that acts as a plant hormone. Symptoms range from misshapen leaves and flowers, thickened stems, stunted growth, flower or leaf abortion to epinasty.
Greenhouse crops are effected differently depending on plant species and growth stage, temperature, length exposed, and concentration of ethylene.
Most plants will eventually recover from ethylene injury. Plants that bloom once a year that are exposed to ethylene while in the flower bud stage will not bloom this year. Exposed plants which flower continuously resume normal leaf growth and flowering within 2 weeks.
An Indicator plant to use for ethylene is a tomato plant because it is highly sensitive and will show signs of ethylene exposure within 24 hours. It only takes 1ppm of ethylene in a few hours to effect tomatoes. Tomato leaves will twist and look distorted, or show signs of wilting (epinasty). The leaf petiole of an epinastic tomato leaf is bent downward like it is wilted yet it is turgid to touch and root system is healthy.
To avoid ethylene injury, unit heaters need proper ventilation and intake of fresh air from outside. One square inch of vent cross section (of outside air) for every 2,500 Btu's of heater output is recommended. Example: A 125,000 Btu heater would need an 8 inch diameter fresh air inlet pipe ( laundry dryer vent hose) which would give 50 square inch of ventilation.
Keep plants separated from auto engine exhaust and small combustion machinery engines.
Ethylene Sources, Symptoms, and Preventions.
http://www.imp.msu.edu/grnhouse07/G1-02-07.htm#2
http://armstrong.extension.psu.edu/Horticu...ylenePhotos.htm
http://www.ces.ncsu.edu/floriculture/hils/HIL530.pdf
