Axillary Bud Development of ‘Shine Muscat’ Grapevine by Treatment of 6-benzylaminopurine, Spermidine, and Light

‘Shine Muscat’ grape production is challenged by the frequent occurrence of empty branches that do not exhibit flowers on the shoot. Therefore, in this study, axillary bud development was investigated by treating with plant growth regulators [6-benzylaminopurine (BAP) and spermidine (SPD)] and an environmental factor (long-day treatment) during ecodormancy and the growth stage to reduce the occurrence of empty branches in ‘Shine Muscat’ grapevine. Treatments with growth regulators and light during ecodormancy did not affect bud size, but flower primordium formation and flower cluster appearance rates were the highest after BAP treatment. Flower primordium formation rate was the most efficient when 200 ppm BAP was applied after endodormancy break. When plants were treated with growth regulators in the growth stage, SPD treatment promoted the growth of shoots and buds but reduced the flower primordium formation rate. In contrast, BAP treatment inhibited bud growth but increased the flower primordium formation rate. In the case of long-day treatment, the formation of the flower primordium was also delayed as in an in vitro experiment. The whole bud necrosis rate was markedly low, and no significant difference was observed after all treatments. The flower primordium formation rates of the first and second buds that are mainly used for the cultivation of ‘Shine Muscat’ were remarkably low. Although BAP treatment promoted the flower primordium formation rate of the first and second buds, it was confirmed that the rate of cluster appearance in the following year was similar to the untreated group. Therefore, we suggest that 200 ppm BAP treatment during ecodormancy is the most efficient approach to reducing the occurrence of empty branches in ‘Shine Muscat’ grapevine. Additional key words: 6-benzylaminopurine, ecodormancy, empty branches, inflorescence primordium, short pruning