Flowering initiation

Valde°s etal. (1987) concluded that plant height is a minor factor in flower initiation. In the Sierra Mazateca, most flowering stems are, in fact, very long, since the stems that elongate the most are most likely to receive direct sunlight. Plants grown in the University of Wisconsin... 

This phenomenon, which varies in intensity in different varieties, is characteristic of many other perennial fruit crops in which flower initials are laid down in the summer of the year before flowering. The sparse flower induction which accompanies a heavy crop was formerly attributed to depletion of the carbohydrate and nitrogenous reserves of the tree but, whilst alternate bearing may have developed as a means by which the tree could conserve its food reserves, the control mechanisms are clearly hormonal in nature. 

Apple cv. Emneth Early. Effect of fruit removal at different times on flower initiation in bourse buds... 

Off year treatments which have been tried in order to decrease flower initiation include -... 

Figure 1. Hormonal factors influencing flower initiation in bourse bud of apple. G = gibberel-lins, C = cytokinins, F = florigin P...

Meijer, W.J.M. and Mathijssen, E.W.J.M., The relations between flower initiation and sink strength of stems and tubers of Jerusalem artichoke Helianthus tuberosus L.), Neth. J. Agric. Sci., 39, 123-135, 1991. 

Ethylene promotes a large array of responses in seeds, plants, and fruits (Table I), some similar to and some dissimilar to effects of auxins. Those with actual or potential commercial application include (a) growth promotion of seedlings (rice), (b) inhibition of height growth, (c) root initiation, (d) chlorophyll destruction (citrus), (e) flower initiation (pineapple, bromeliads), (f) stimulation of fruit growth (figs). 

Pigment synthesis inhibition Flower initiation Flower inhibition Flower sex shifts Fruit growth stimulation Fruit degreening Fruit ripening Respiratory changes Storage product hydrolysis Latex secretion promotion... 

Figure 2. Different stages of growth in Ileracleum candicans field emergence (A) true-leaf initiation (B) vegetative growth (C) flowering initiation (D) blooming (E) pollination by insect (F) fruiting (G) final growth (FI) and harvested rhizome (I).

Nagao, A. (1983) Differences of flower initiation of Cryptomeria japonica under various alternating temperatures. J. Jap. For. Soc., 65 335-338 (in Japanese). 

Another possible reason why GA treatments do not induce flower initiation may be due to improper timing and/or supraoptimal doses. For example, exogenous GAs either promoted or inhibited flower formation (as measured by number of flower buds produced) in plants of the dwarf strain Kidachi of the SDP Pharbitis nil that were marginally induced by 1 inductive long night. Promotion of flowering was observed when the GA treatment occurred 11 to 17 h before the inductive dark period, while GA application immediately after the inductive dark period caused a reduction in the flowering response [9, 18]. 

Are Endogenous GA Levels Correlated with Flower Initiation ... 

Any attempt to rigorously define the role of a hormone in the regulation of a developmental process requires determination of the quantitative relationships between hormone levels and the process. To date, there are few studies in which changes in GA levels in relation to flower initiation have been carefully monitored. Part of the problem has been that most investigations rely on bioassays for quantitative analyses the reliability of this method of quantitation has been... 

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