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Timothy J. Hudelson, F. Mitchell Westmoreland, and Bruce Bugbee

Ethylene is an essential plant hormone at low concentrations. Concentrations in the field rarely exceed 5 nmol⋅mol−1 (0.005 ppm), but it can accumulate as a gas in closed, indoor environments. These elevated levels can reduce growth and yield. Temperature alters ethylene synthesis and has the potential to influence ethylene sensitivity of crop plants in sealed greenhouses and indoor environments. We studied ethylene sensitivity of tomatoes (Solanum lycopersicum L. cv. MicroTina) using a unique, 12-chamber system. Ethylene levels of 0, 20, and 40 nmol⋅mol−1 (parts per billion) were maintained throughout the life cycle, at an air temperature of 22 or 28 °C. Yield of red fruit was three times higher at 22 than at 28 °C. There was a steady decrease in yield with increasing ethylene concentration, but vegetative growth was reduced less than 10% in any treatment. The highest ethylene concentration reduced yield to 11% of the control at 22 °C and to 4% of the control at 28 °C; the intermediate ethylene level reduced yield to 51% of the control at 22 °C and 37% at 28 °C. Regardless of temperature, filtering of ethylene in indoor environments to below 20 nmol⋅mol−1 is necessary to achieve normal fruit set and yield in tomato.