Plants of `Brightwell' and `Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) were subjected to 0, -1, -3, or -4.5 °C for 1 hour during flowering. After treatment, half of the plants were exposed to bees (Bombus sp.) only, and half were exposed to bees and received applications of GA3. Fruit set of both `Brightwell' and `Tifblue' pollinated by bees declined sharply after exposure to -1 °C for 1 hour, but there was no visible damage to corollas, styles, and ovaries. Fruit set of GA3-treated plants of both cultivars equaled that of control plants (plants having no cold exposure) at temperatures ≥+-3 °C. Both pollinated and GA3-treated plants had ≤2% fruit set after exposure of flowers to -4.5 °C. Both prefreeze and postfreeze applications of GA3 were beneficial for fruit set. Assessment of flower part damage at the different temperatures indicated corollas were most sensitive to freeze damage, followed by styles, and then ovaries. Results suggest fertilization and fruit set of pollinated rabbiteye blueberries can be greatly impaired by even mild freezes (-1 to -2 °C), whereas, appropriately timed applications of GA3 can result in little reduction in fruit set even after moderate freezes (-3 to -4 °C) of blueberries during bloom. Chemical name used: gibberellic acid (GA3).
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