Apple fruitlet growth responses to temperature were studied, for different durations following bloom (DAFB), under controlled environment (CE) conditions. Container-grown trees of `Red Delicious', `Golden Delicious', `Braeburn', `Fuji', and `Royal Gala' were placed in different maximum/minimum temperature regimes, ranging from 9/3 to 25/15°C for various periods, including 10–40, 10–80, and 40–80 DAFB. Temperature treatments were selected to identify possible differences between mean and maximum/minimum differential effects Trees were placed outdoors following the CE treatment to allow impacts on subsequent fruit development to be determined. The impact of temperature was dramatic. For example, fruit expansion rate for `Red Delicious' varied from 0.12 mm/day at 9/3°C to 0.98 mm/day at 25/15°C. Furthermore, the cell division phase was considerably longer under cooler temperatures. The influence of post-bloom temperature, for even short durations, was evident at harvest in both fruit size and in different fruit maturity indices. Differences in temperature sensitivity were evident amongscultivars. A detailed model has been developed to integrate the responses that have been determined.
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