What is the primary hormone that influences apical bud dominance?

The primary hormone that influences apical bud dominance is auxin. Auxin, specifically indole-3-acetic acid (IAA), is produced at the tips of growing shoots and plays a critical role in controlling plant growth and development. It promotes cell elongation and is instrumental in establishing the pattern of growth where the main shoot grows more vigorously than the lateral buds. This dominance occurs because auxin inhibits the growth of lateral buds; as it moves down from the apical bud, it promotes elongation of the stem while suppressing the lateral buds, effectively maintaining the apical dominance.

Understanding this concept is vital in managing plant growth and development, particularly in landscape management and horticulture, where manipulating apical dominance can help shape plant forms and control their overall structure. Additionally, the other hormones mentioned, such as cytokinin, gibberellin, and ethylene, do have roles in plant growth and development, but they do not primarily regulate apical dominance like auxin does. For example, cytokinins are known to promote lateral bud growth and cell division, gibberellins enhance stem elongation and seed germination, while ethylene primarily regulates fruit ripening and responses to stress.