Fruit Abscission in Rabbiteye Blueberry in Response to Organ Removal and Mechanical Wounding

Fruit abscission in blueberry ( Vaccinium sp.) occurs at the pedicel/peduncle junction (PPJ). Growth regulators such as methyl jasmonate (MeJa) and ethephon accelerate the progression of abscission at this zone. It is not known whether the abscission zone at the PPJ is sufficient to perceive and respond to these growth regulator applications or if the fruit and leaf tissues are required to elicit these responses. Furthermore, the effects of injury to the fruit and leaves on fruit detachment responses have not been previously reported in blueberry. In this study, the requirement of the fruit and leaves to respond to MeJa and ethephon applications was investigated through organ removal treatments in rabbiteye blueberry. Removal of the fruit or the fruit and leaves on the branch followed by MeJa application delayed the progression of abscission at the PPJ suggesting that the fruit tissue is required only to accelerate the progression of fruit detachment in response to MeJa. Interestingly, the extent of fruit/pedicel detachment in response to ethephon applications was higher in the organ removal treatments compared with the control indicating that the PPJ was sufficient to perceive and respond to ethephon and that wounding caused by organ removal synergistically enhanced fruit abscission in response to ethephon. Mechanical wounding of the fruit by removing the distal half of the berry resulted in accelerated fruit detachment at the PPJ. Detachment of non-injured fruit was unaffected by mechanical wounding of adjacent fruit. These data suggest that wounding generates a local signal capable of accelerating fruit abscission at the PPJ. This information may have implications for fruit retention or drop in response to injury to the fruit as caused by herbivore feeding or as a result of insects and pathogens.