Late-harvested apple fruit generally are less responsive to 1-MCP than early harvested fruit, but the effect of harvest date on these responses can vary greatly by cultivar. Little is known about the relationships between internal ethylene concentration (IEC) and responses of fruit to 1-MCP. We have investigated the effects of 1-MCP on `McIntosh', `Cortland', and `Empire' apples in two experiments. In the first, fruit of each cultivar were picked three to five times during the normal harvest season, untreated or treated with 1 μL·L-1 1-MCP, and stored in air. Fruit IEC and firmness were then measured at monthly intervals for 4 months. In the second experiment, fruit were harvested several times during maturation, and, at each harvest, fruit were categorized into groups based on their IEC (<0.5, 0.5–1.0, 1–10, 10–50, 50–100; and >100 μL·L-1), treated with 1 μL·L-1 1-MCP for 24 hours at room temperature, and stored in air. The IEC and firmness of each fruit was then measured at set intervals during storage. Increasing IECs were associated with declining effectiveness of 1-MCP, but the individual fruit study showed that, even in high-IEC fruit, there was an initial inhibition of IEC values during storage before the IECs increased. A Lower IEC at harvest indicated a longer delay before the IEC ultimately increased. Collectively, the data show that it should be possible to determine the response of fruit to 1-MCP based on their IEC.
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