Citrus Shoot Age Requirements to Fulfill Flowering Potential
Three hurricanes from late summer through the fall of 2004 caused severe leaf loss, sometimes over the same citrus production areas in Florida. A vegetative flush occurred after each hurricane, and by December, new shoots were 3 to 12 weeks old prior to trees accumulating over half the cool temperatures required for good flower bud induction. Two experiments were conducted to evaluate the potential for young flushes to develop buds that could be induced to flower. Flushes on potted trees in a greenhouse were stimulated and shoots were allowed to develop 4 to 10 weeks before moving the trees to cool, flower-inducing conditions for 6 weeks in a growth chamber (15/10 °C, day/night). Plants were subsequently returned to the greenhouse, which was at 20 °C or higher (ambient), until buds sprouted. In both experiments, less than 2% of sprouting buds flowered on shoots that had developed for only 4 weeks. Sprouting buds flowered on 25% and 76% of the shoots that had developed for 6 weeks in the first and second experiments, respectively. After 8 to 10 weeks of shoot development, sprouted buds that flowered increased to 54% in Experiment 1 and were 50% in Experiment 2. Consequently, more than 4 weeks of shoot development were necessary for citrus shoots and/or their leaves to reach their maximum flowering level in these experiments. In the second experiment, conducted during the following year, fewer buds sprouted, possibly due to low carbohydrate levels in new leaves after repeated cycles of forced flushing and root restriction in the greenhouse.