The effects of water stress and GA, on breaking dormancy of flower buds of coffee (Coffea arabica L.) were investigated. In the first experiment, water was withheld until the trees reached leaf water potentials (WP) of -1.20, - 1.75, -2.65, or -3.50 MPa. Water potential, ethylene production, and ion leakage of flower buds and leaf disks were examined from release from water stress until anthesis. Trees that had experienced leaf WP of less than - 2.65 MPa, and flower bud WP of about - 4.0 MPa flowered within 9 days after irrigation. In flower buds where dormancy had been broken with water stress, ethylene production was low compared to dormant buds and flowers at anthesis. In the second experiment, O, 50, 100, or 200 mg GA3/liter was painted on branches of nonstressed trees. In experiment three, water was withheld until plants reached leaf WP of -0.6, -1.3, - 2.1, or - 3.0 MPa, then two branches per tree were painted with O, 50, and 100 mg GA3/liter. Gibberellic acid partially compensated for insufficient water stress to initiate flower opening. Ethylene evolution of flower buds was affected by water stress but not by GA3 treatment. Severe water stress treatments and GA, treatment (200 mg·liter-1) increased ethylene evolution of leaf disks. Ion leakage of flower buds and leaf disks was increased by severe water stress. Ion leakage of flower buds was highest at anthesis. After water stress, dormant and nondormant flower buds at the 4-mm stage could be distinguished based on their ethylene evolution. Chemical name used: gibberellic acid (GA3).
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