Effect of Ethrel, Abscisic Acid, and a Morphactin on Flower and Berry Abscission and Shoot Growth in Vitis vinifera1

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Abstract
The effect of 3 abscission-promoting compounds on flower and berry abscission in 4 varieties of Vitis vinifera grapes was studied. A cluster-dipping experiment with Ethrel, abscisic acid, and a morphactin at concentrations ranging from 0.1 to 1,000 ppm, was done using ‘Thompson Seedless’, ‘Carignane’, and ‘Muscat of Alexandria’, at 4 developmental stages. Stimulation of abscission by the growth regulators decreased as flowers and berries became older. The morphactin was the most effective and abscisic acid the least effective in promoting abscission. Spray treatments with the same compounds induced abscission on ‘Muscat of Alexandria’ and ‘Perlette’ at appropriate concentrations. Pretreatment of ‘Muscat of Alexandria’ clusters with 4-CPA eliminated the effectiveness of morphactin and, to some extent, that of Ethrel. Morphactin at 1 ppm stimulated shoot growth of ‘Muscat of Alexandria’ but marked inhibition occurred at 100 and 1,000 ppm. Ethrel at 10 ppm stimulated shoot growth, but marked inhibition occurred at 100 and 1,000 ppm. With ‘Carignane’ only morphactin produced inhibition of shoot growth. Appropriate concentrations of these compounds applied as sprays thinned ‘Perlette’ grapes, but thinning was quite irregular both within and among clusters.

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