The Flowering Process ofVitis vinifera: A Review

Abstract

The flowering of <i>Vitis vinifera</i> spreads over two seasons. Tendrils and inflorescences have a common origin known as anlage or uncommitted primordia. The fate of the uncommitted primordia depends on the cytokinin-gibberellin balance, with cytokinins promoting transition to flowering and gibberellins inhibiting it. High temperature and high light are induction stimuli for flowering. Neither photoperiod nor vernalization is very relevant for flowering induction. Inflorescence primordia development in latent buds stops after the formation of secondary and tertiary branches, approximately one month before shoot periderm formation. Buds resume growth after dormancy, with further branching of inflorescences before differentiation of individual flowers. Warm weather at budburst favors further inflorescence differentiation, resulting in more clusters per shoot, while cool weather favors differentiation of more flowers per clusters and fewer clusters per shoot. Environment and cultural practices influence flowering, either directly or indirectly via their impact on photosynthesis and nutrient availability. Cultural practices encouraging light penetration into the canopy favor flower initiation, while practices resulting in shading have a detrimental impact. Flower formation occurs through a series of sequential steps under hormone-mediated genetic control. The first genetic change involves the switch from the vegetative to the floral state, in response to different environmental and developmental signals, through the activity of floral-meristem identity genes. Second, the floral meristem is patterned into the whorls of organ primordia through the activity of floral-organ identity genes. Third, the floral-organ identity genes activate downstream effectors that specify the various tissues which constitute the different floral structures. The flowers are hermaphroditic and most are self-pollinated but cross-pollination also occurs. Fertilization is hindered by cool rainy weather and favored by warm dry weather.