Bud Development in Vitis vinifera L.

The development of the complex hierarchy of axillary buds in Vitis vinifera L. cv Cabernet Sauvignon is described. Developmental differences between lateral and compound buds and between the compound bud and the apex of the growing shoot are discussed. Differences include the position and timing of bud initiation, the position of the first uncommitted primordium and the timing of its differentiation, and the ability of the compound bud to overwinter in a dormant state. Evidence confirming the monopodial development of the grape shoot includes the persistence of first-order axillary buds in each leaf axil of this species regardless of the position of the node relative to inflorescence or tendril insertion, the uninterrupted plane of phyllotaxy in field-grown vines, and morphological evidence of the lateral origin of uncommitted primordia. The initiation and early development of tendril and inflorescence primordia are described, and evidence supporting Bugnon's interpretation of these organs as shoot homologs is discussed. Shoot development in V. vinifera is interpreted as a highly modified form of distichous phyllotaxy in which each node bears a single leaf or modified leaf subtending an axillary bud or bud homolog. Some nodes bear foliage leaves subtending lateral buds; other nodes bear modified leaves (bracts) subtending bud homologs (tendrils or inflorescences). The unusual position of tendrils and inflorescences opposite the leaf results from the failure of the internodes separating bract-bearing nodes from leaf-bearing nodes to elongate.