S23 - Session O8 - Lower concentrations of 1-MCP require longer exposure times to inhibit apple fruit ripening

Authors: Randolph M. Beaudry *, Nobuko Sugimoto, Philip Engelgau

1-Methylcyclopropene (1-MCP) is an important synthetic plant growth regulator used to delay ripening and senescence of apple fruit during postharvest storage. The commercial label rate varies between 600 and 1000 ppb. We evaluated the response of three cultivars of apple fruit (Delicious, Granny Smith and Evercrisp) to varying concentrations of 1-MCP by measuring the suppression of ethylene synthesis and delay in fruit softening for fruit held at 3 °C during the treatment period, followed by up to 2 weeks at room temperature. Concentrations to which apple fruit were exposed spanned 100,000-fold, from 1 ppb to 100 ppm and the exposure times varied between 0.5 min and 14 d. At the lowest concentration range provided (0, 1, 5, 10, 20, 50, and 100 ppb), fruit responded to as little as 20 ppb, but 100 ppb was required for maximal suppression of ethylene biosynthesis and the full impact was not achieved until fruit had been exposed to this concentration for 10 to 14 days. Fruit exposed to 10 ppm responded in as little as 10 min, but were fully impacted within 30 min exposure. Fruit exposed to 100 ppm responded in as little as 1 min, but were fully impacted within 5 to 10 min. Internal 1-MCP levels in apple fruit typically ranged between 1/3 to 2/3 that of the treatment dose for fruit exposed to 1-MCP for 24 h or more. Evercrisp fruit had no response to even the highest 1-MCP levels provided, suggesting some cultivars of apple may be 1-MCP insensitive and, potentially, may also be insensitive to ethylene. The data make the argument that low, continuous, or near continuous doses of 1-MCP might effectively suppress ripening of apple. Alternatively, use of short exposures to high to very high concentrations might also be a useful strategy to inhibit fruit ripening, provided residue levels prove to be within acceptable limits.