Unravelling the mechanism of mango flowering

Issue Date

4-2009

Abstract

A mango flowering model previously presented (Protacio, 2000) had three assumptions: (1) Gibberellic acid (GA) is a floral inhibitor that prevents a mature mango tree from flowering (2) Decreased GA levels beyond a certain threshold leads to the development of floral initials probably through the accumulation of carbohydrates (3) Floral bud break will occur when sprayed with "flower-inducing" chemicals like potassium nitrate, thiourea or ethylene. This model was tested using 13-year old 'Carabao' mango trees wherein the level of gibberellic acid (GA3) was artificially reduced through application of 1.0 gram of paclobutrazol (PBZ) per meter canopy diameter. Levels of GA3, total non-structural carbohydrates, and presence of floral initials in the terminal shoots were followed monthly. Three months after PBZ application, GA3 content of shoots in PBZ- treated trees decreased by more than 79% compared to the control. At this time, 56% of the terminal shoots in PBZ-treated trees had floral initials and none in the control trees. By the fourth month, shoots with floral initials in PBZ-treated trees increased to 86% while 42% of the control trees also had floral initials just before KNO 3 was sprayed. At the same time, a peak in the 1-aminocyclopropane 1-carboxylic acid levels also coincided with the development of floral initials in PBZ-treated trees; indicating a possible involvement of the ethylene biosynthetic pathway in floral initiation in mango. The development of floral initials was accompanied by a decrease in GA3 levels and a concomitant increase in starch levels in the apical buds, leaves and stem. Induction of flower bud break by 2% KNO3 resulted in a flower intensity index of 4 (flowers all over the canopy) and longer inflorescences in PBZ-treated trees while control trees exhibited a flower intensity index of 2 (less than 25% of the canopy have flowers). This study validated the model by demonstrating that mango shoots must have low GA content to allow total non-structural carbohydrates, primarily starch, to accumulate in the leaves and buds leading to the early formation of floral initials. Floral initials were present before KNO3 application indicating that this chemical merely induces bud break of quiescent pre-existing floral buds and is not responsible for the transformation of vegetative buds to reproductive ones.

Source or Periodical Title

Acta Horticulturae

ISSN

5677572

Volume

820

Page

259-270

Document Type

Article

College

College of Arts and Sciences (CAS)

Language

English

Subject

1-aminocyclo-propane 1-carboxylic acid, Ethylene, Gibberellic acid, Paclobutrazol, Potassium nitrate

Identifier

https://doi.org/10.17660/ActaHortic.2009.820.29

Digital Copy

none

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