Processes Influencing Floral Initiation and Bloom: The Role of Phytohormones in a Conceptual Flowering Model

Abstract

The reproductive phenologies of temperate fruit tree species are briefly introduced and compared to the reproductive phenologies of three tropical and subtropical fruit tree species. The impact of leaf and fruit development and the phytohormones they may produce on the reproductive or vegetative fate of bourse buds in apple spurs serves as the model to discuss temperate fruit flowering. In contrast, conceptual models of citrus (Citrus L.), mango (Mangifera indica L.), and lychee (Litchi chinensis Sonn.) flowering are described which propose physiological mechanisms for both flowering and vegetative flushing in trees grown in subtropical and tropical environments. Possible roles for auxin and cytokinins in shoot initiation and for gibberellins and a putative florigenic promoter in induction are discussed as they relate to the physiology of flowering and vegetative flushing of tropical species. Successful application of these conceptual flowering models through the use of growth regulators and other horticultural management techniques to control flowering of citrus, mango, and lychee is described.