Effects of Early Gibberellin Treatment on Flower Elongation, Berry Density, Labor Time, and Fruit Quality in Open-field-grown Grape ‘Shine Muscat’

Abstract

Seedless grape cultivation requires a lot of cultivation management in a short period of time, which is a factor that hinders scale expansion, but a similar problem has been pointed out with ‘Shine Muscat’, where the cultivation area is rapidly increasing. Therefore, a more labor-saving technique is required. We considered early Gibberellin acid (GA₃) treatment, which has been put into practical use for ‘Sunny Rouge’, and conducted GA₃ treatment of ‘Shine Muscat’ at the early 7 to 8 leaf spreading stage, and elongation of the flower cluster decreased the berry density. In addition, by applying early GA₃ treatment and thinning the flower cluster when it reached a length equal to or longer than the beginning of flowering, it is possible to reduce the labor time necessary for berry thinning without increasing that for flower thinning, compared with GA₃ treatment at full bloom and thinning the flower cluster at the beginning of flowering. Regarding fruit quality, early GA₃ treatment was suggested to improve the sugar content and taste, and it was considered that there would be no major effect on the ease of eating the fruit with the skin, but there was concern that the grade would decline due to a deterioration in grape bunch shape.