Physiology of Flowering in the Grapevine — a Review

The vegetative and reproductive anatomy of the grapevine is discussed with emphasis on recent interpretations based on scanning electron microscopy. The terminology of flowering in Vitis is defined and a developmental code, comprising Stages 0 to 11, is proposed for the events leading to formation of flowers. In brief, flowering in the grapevine involves three main steps: 1) Formation of Anlagen or uncommitted primordia (Stages 0 to 1); 2) Differentiation of Anlagen to form inflorescence primordia (Stages 2 to 7); and 3) Differentiation of flowers (Stages 8 to 11). The literature on the factors that influence flowering in grapes is reviewed under three major headings: 1) Biochemical changes in apices during inflorescence primordia formation; 2) Effects of environmental factors, including temperature, light intensity, photoperiod, water stress and mineral nutrition and 3) Role of phytohormones. Anlagen develop into inflorescences, tendrils or shoots depending on the environment and hormonal factors. A hypothetical scheme for the hormonal control of Anlagen, tendril and inflorescence formation is proposed. It is suggested that flowering in grapes is controlled by the gibberellin:cytokinin balance. Formation of the inflorescence axis (the Anlage) is gibberellin controlled, but subsequent differentiation into flowers is regulated by cytokinin.