gibberellins, naturally occurring plant hormones which regulate vine growth as for other plants. Isolated in 1941 from a rice fungus, they have been much studied since. In the vine they are formed in growing tissue in the leaves, roots, and berries. Many thousands of hectares of Thompson Seedless (sultana) vines are treated by spraying with gibberellins during flowering and shortly afterwards, and this results in larger berries suitable as table grapes. Other seedless varieties respond similarly to this treatment. Trials at geisenheim and Oppenheim in Germany involving the application of gibberellic acid to seeded grapes during full bloom, causing berry shatter (see fruit set), resulted in a substantial reduction in both botrytis infection and the development of sour rot. The technique is already in commercial use in northern Italy and has proved to be an important way to reduce botrytis problems in Italy and Germany.
