Morphactins induce berry abscission in grapes

Two derivatives of fluorene-9-carboxylic acid (termed morphactins because they produce morphological changes and striking suppression of growth in plant species) were tested on seeded Vitis vinifera, Muscat of Alexandria; and seedless Thompson Seedless, and Black Corinth grapes. Berry abscission was induced when the compounds were applied at the fruit-set stage or two weeks later. When morphactins were applied near maturity, no berry drop occurred although the strength of berry attachment was reduced. An auxin (4-CPA) counteracted the morphactin response, indicating that the response may involve auxin metabolism. These chemicals are not registered for use in the U.S. at this time except by researchers on an experimental basis.