Identification of active substances in garlic responsible for breaking bud dormancy in grapevines

The active substances in garlic responsible for breaking bud dormancy in grapevines were investigated by employing single bud cuttings of 'Kyoho' (Vitis vinifera x V. labruscana Bailey). Four major gas-chromatographic peaks were detected in the essential oil extracted from freshly grated garlic cloves and commercial garlic oil, but only the first two peaks were found in volatiles from freshly grated garlic and commercial garlic oil. Based on a comparison of the retention time with authentic chemicals and GC-MS analysis, the compounds were identified as diallyl mono-, di-, tri-, and tetra-sulfides. The highest peak was diallyl disulfide, followed by diallyl tri-, mono-, and tetra-sulfides, but only trace amounts of dimethyl mono- and di-sulfides were present. When painted to the upper cross-sectional cut surface of cuttings, dimethyl disulfide and diallyl disulfide greatly promoted budbreak. Diallyl trisulfide treatment resulted in a rate of budbreak that was not uniform, although the first budbreak was accelerated. Exposure to volatiles of diallyl di- and tri-sulfides was the most effective treatment in promoting budbreak, irrespective of the concentration and the duration of exposure. However, exposure of cuttings to volatiles of 30% dimethyl disulfide suspension markedly inhibited budbreak, although both authentic dimethyl disulfide (a.i. 99%) and its 10% suspension promoted budbreak. The effects of dimethyl sulfide and diallyl sulfide on budbreak varied among the concentrations and the duration of exposure. These results indicate that the active substances in garlic, responsible for breaking bud dormancy in grapevines, are sulfur-containing compounds with an allyl group (CH2CHCH2), particularly diallyl disulfide.