Abstract:
Coffee trees growing in the Kona district of Hawaii
were treated with different concentrations of either BA,
GA3, or Promalin, and pruned at the time of flowering. No
significant differences in the flowering and fruit ripening
pattern were found. High concentrations (100 mg/1) of
growth regulators decreased fruit fresh weight. Pruning
yielded the lowest number of fruit and flowers, and caused
branch dieback. Fruit set was between 46 and 83% for the
two years studied.
Flower buds from trees growing in the field that were
>4 mm, but not developed to the candle stage at the time of
GA₃ treatment, reached anthesis 20 days earlier than the
controls. Their development was independent of rainfall,
unlike the controls. Fruit from buds that had been treated
at the >4 mm or the candle stage ripened more synchronously
and earlier than the control. Buds smaller than 4 mm did
not respond to GA₃ treatment.
A threshold leaf water potential of -2.7 MPa, and
flower bud water potential of about -4.0 MPa was necessary
to overcome dormancy of flower buds in greenhouse grown
trees. GA₃ stimulated anthesis in some plants that were
stressed to leaf water potentials of -2.1 MPa. Ethylene
evolution of flower buds where dormancy had been broken
with water stress was low, compared to dormant flower buds.
At anthesis, ethylene evolution reached highest levels.
Free and conjugated IAA levels in flower buds changed
markedly after the dormancy breaking stimulus. Doubling
of fresh and dry weight of flower buds occurred 3 to 5 days
after water stressed plants were rehydrated. It was
preceded by an increase in free IAA, and a tripling in the
rate of water uptake from 1 to 3 days after rehydrating
water stressed plants. Throughout the development, the
largest percentage of IAA was present in the conjugated
form.
