Flower Induction – Hormonal and Substrate Control

Karthik-Joseph John

Horticultural Sciences Department University of Florida

Monselise and Halevy. 1964. Chemical Inhibition and Promotion of Citrus Flower Bud Induction.

Gibberellic acid inhibits flower formation in

apples, pears, peaches and many other plants

First paper to study the effect of GA on citrus

flower induction

Study the GA effect on citrus and to better

understand the timing of bud induction

Use of anti-GA or other growth regulators to

induce flowering in lemons as an alternative to

withholding irrigation

Introduction

Experiment 1:

Shamouti oranges – 1 branch/tree on the

southern part of each tree

Treatments – 200 ppm of GA sprays for 3, 4, 5 or

6 times at 2-week intervals from November 3

4 replications per treatment

Flowers were counted on the branches on April 5

Sprouting vegetative buds were recorded on

January 1 and February 12

Materials and Methods

Experiment 2:

Eureka lemons – 2 branches/tree on the

south-eastern side

Treatments – 2 sprays of 0.2% Cycocel, 0.2%

B Nine, 50ppm BTOA or 500ppm GA

Flower buds, flowers and fruitlets less than 2

cm in diameter were counted on Nov. 4

Withhold irrigation for 2 months starting mid-

august???

Materials and Methods

Experiment 1:

GA spray inhibited flower formation

GA treatment delayed flower differentiation

Results and Discussion

No statistics

Very few flowers

differentiate if GA effect

lasts during the main

induction period

Results and Discussion

No statistics

Experiment 2: No flowering in control and GA treated trees BTOA induced maximum flowering

Results and Discussion

No statistics

Effect of BTOA on citrus leaves

Rolling of leaf margins in leaves of the new growth produced under the influence of the chemical

Formation of flower clusters at the apex of the young branches

Results and Discussion

“Leaf symptoms found with GA are well known”

Abstract is missing

Experimental design is not mentioned

Only southern part of the tree is used – so results may not represent the overall effect

What is the basis for selecting the conc. of GA?

No statistical analysis

In experiment 1, data for measurements on Jan 1 is missing

No details on the leaf symptoms due to GA

Typing error?

Overview

Discussion

Guardiola et al. 1977. Gibberellic acid and flower bud development in sweet orange.

Introduction

The inhibitory effect of GA is used to control alternate bearing

The mechanism of the inhibitory action is unknown

Earlier hypothesis:

GA interferes with flower induction

GA may reverse flower bud to a vegetative apex through an indirect mechanism

A different mechanism of action of GA on flowering is observed

Sweet orange trees – Navelate and Washington navel

No other details were given in materials and methods

Materials and Methods

GA sprays during winter greatly reduced flowering

The effect depends on the concentration and time of application

Results and Discussion

Absolute values

were not

presented

There is decrease in the leafless type of

inflorescences with a parallel increase in the

vegetative shoots

Results and Discussion

Number of leaves per shoot increased but

there was no change in the number of flowers

Results and Discussion

Inhibition in flowering is mainly due to decrease

in number of shoots of RF and S types

Results and Discussion

The buds in the more apical nodes started growth earlier and in a greater number than in the more basal

GA did not affect the proportion of shoots which abscise during early phases of development

Results and Discussion

No statistics shown in figure

The main effect of GA lies in the inhibition of bud

development

Insufficient information about the materials and

methods

Statistical analysis is not show for the figure

Results and interpretation were difficult to

understand

Overview

Discussion

Davenport. 1983. Daminozide and Gibberellin Effects on Floral Induction of Citrus latifolia.

Tahiti limes grown in southern Florida are ever

bearing

Heavy flushes of flowers – Jan., Feb. and March

Fewer flowers – several times throughout the

year

Majority of production – summer months

It is desirable to induce heavy flowering in any

flush to increase off season crop

Introduction

Materials and Methods

18 year old Tahiti lime trees

3 treatments – 0.1mM GA, 2500 ppm daminozide and distilled water control

4 replications per treatment

First experiment:

Treatments applied in mid-August at the onset of summer flush

3 sprays in one week period

Daminozide concentration – 500 ppm

Total number of new shoot and shoot type were observed in mid-September

Materials and Methods

Second experiment:

First spray was done in mid-December, prior to spring flush

2 weekly sprays of 500 ppm daminozide followed by 4 weekly sprays of 1000 ppm

These were followed by 2500 ppm daminozide prior to and during the spring flush

GA and control were applied at all times

The flush was vegetative which is typical for that time of year

No tendency to flower in daminozide treatment GA increased the number of shoots produced The morphology of vegetative shoots in the GA

treatment was comparable to control and daminozide treatment

Results and Discussion

GA treatment shifted shoot type from predominantly flowering to mainly vegetative

Daminozide inhibited flowering

Results and Discussion

Materials and methods were not organized

together

Details of experimental design and statistical

analysis were not mentioned

The data from the west side of the trees are not

reliable – the western side was crowded due to

closely placed adjacent rows and so there was

shading and also the sprays were unable to

cover completely on this side

Overview

Discussion

Garcia-Luis et al. 1986. Inhibition of flowering in vivo by existing fruits and applied growth regulators in Citrus unshiu

Flowering in citrus is inversely related to the

previous crop

This could be due to an interference in the build-

up of reserves and hormonal imbalance

This study investigates the time course of

flowering inhibition by the fruit

This effect is compared to the application of GA

Also studied the effect of kinetin, ABA and 2,4-D

Introduction

10 year old Owari Satsuma mandarin Randomized Block Design with single whole

tree replicates 5 µL drop of 200 ppm solution of growth

regulator was placed directly on the bud Growth regulators GA, ABA, kinetin and 2,4-D

were used 10 most apical buds from each twig from

previous summer were selected 20 twigs were selected for each compound Application – from middle Dec. to middle Jan. Whole tree spray was also done using the

chemicals

Materials and Methods

Only GA reduced the number of sprouted nodes

Results and discussion

Similar response was obtained when GA and kinetin were applied to entire tree instead of locally to the buds

Results and discussion

Influence of time of GA application on flowering

Results and discussion

No statistics

Results and discussion

Influence of time of GA application on spouting

Most data support the work done earlier

The inhibitory effect of GA and kinetin on bud

sprouting contrasts with the promotive effect

found when applied to non-flowering seedlings

and young trees

Good experimental design

Statistics is done but no statistics is shown for

figure 3

Overview

Discussion

Koshita et al. 1999. Involvement of endogenous plant hormones (IAA, ABA, GAs) in leaves and flower bud formation of satsuma mandarin (Citrus unshiu Marc.)

This paper investigates the effect of the levels

of endogenous plant hormones in relation to

flowering

The relation to other plant hormones was not

simultaneously investigated

The aim of this study is to clarify the

relationship between flower bud formation and

plant hormones (IAA, ABA, GA1/3, GA4/7)

contents

Introduction

25 year old satsuma mandarin

8 lateral branches consisting of only vegetative

shoots were chosen in each tree

4 of them are ringed

60 fruit bearing shoots are selected in each tree

Materials and Methods

Results and Discussion

IAA and

ABA

contents in

the leaves

Results and Discussion

GA

content in

the leaves

Results and Discussion

In October, higher endogenous GA levels may be one of the reasons for vegetative growth in the following spring

In Dec. and Feb. only slight difference was observed in GA content between bearing and vegetative shoots – this supports the work of others

Increase of leafless inflorescence and enhancement of ABA in Dec. and Feb. and of IAA in Dec. suggests that endogenous ABA and IAA may affect flower bud development

Overview

Discussion

Jona et al. 1971. Further Studies on the Effect of Nucleic Acids on Shoot and Flower Formation in Citrus Trees.

Introduction

FUdR is a specific DNA synthesis inhibitor

which promotes flowering in citrus

This controls flower formation at the stage of

cell division in the growing apex

This paper deals with the effects of this

chemical on flower and shoot formation

The role of cell division in flower formation was

studied by applying FUdR and TdR during the

induction and differentiation period

36 year old Shamouti orange trees

TdR and FUdR were applied either alone or in combinations at 10-3 M

Each chemical solution was brushed on leaves, stem and buds of 10 spring branches beginning Oct. 17

Application was repeated at 10 day intervals

There were 2 series of treatments. In one the last treatment was applied on Dec. 17 and in another on Jan. 18

Materials and Methods

Effects on the number of sprouting buds during the spring flush

Results and Discussion

No statistics

Effects on the number of lateral shoots developing

during the spring flush

Results and Discussion

No statistics

Effects on the number of lateral shoots per

sprouting internode during the spring flush

Results and Discussion

No statistics

Effects on the type of new lateral shoots

No significant difference when FUdR or TdR are applied separately

Results and Discussion

No statistics

Effects on flower formation

Results and Discussion

Effects on mitotic activity in the apex during floral

induction and differentiation

Results and Discussion

FUdR is a DNA synthesis inhibitor and it can affect RNA synthesis when it is converted to 5-Fluorouracil

TdR may counteract the effect of FUdR on DNA but not on RNA

So, the inhibition of RNA synthesis is crucial for the promotion and bud opening

Thus, FUdR + TdR promotes flower formation by interfering with RNA metabolism

No details on experimental design were given They have mentioned the use of std. errors and

multiple range test, but they were not shown in the graphs

Overview

Discussion

Goldschmidt et al. 1985. A Role for Carbohydrate Levels in the Control of Flowering in Citrus.

Carbohydrate levels have been suggested as a

limiting factor for flower formation in citrus

In this study, they examined several lines of

evidence for the role of carbohydrates and their

possible interaction with other factors in the

control of flowering

Introduction

Materials and Methods

Mature, shy bearing Shamouti orange trees

Girdling was done in late October

Half of control and half of girdled trees were sprayed with 72 µM GA in Nov. and Dec.

3 year old potted Minneola tangelo were used in another experiment in which plants are subjected to various day/night temperatures

Effects of girdling on starch and flowering There is correlation between elevated

carbohydrate levels and flowering

Results and Discussion

Starch contents in leaves and twigs as affected by GA and girdling

Results and Discussion

Effect of GA and girdling on shoot type

GA counteracted the girdling effect

Results and Discussion

Quantitative effects of cool temperatures on the promotion of flowering

Starch levels did not correlate well with flowering Intensity of flowering was in accordance with the

exposure to cold temperatures

Results and Discussion

Carbohydrate levels play a role in flower

induction but it is not always the limiting factor

More details could have been added in the

Materials and Methods section e.g.. Light

intensities used for the experiments

Experimental design and statistical methods

were not explained in the Materials and Methods.

But statistics is well explained for each table

Overview

Discussion

Monerri and Guardiola. 2001. Peroxidase activity and isoenzyme profile in buds and leaves in relation to flowering in satsuma mandarin.

Changes in peroxidase activity and isoenzyme

profiles have been described during flower

induction in other species

The aim of this work is to determine if the

changes in peroxidase activity and isoenzyme

profiles can be related to the developmental

states of the buds

They have compared the seasonal changes in

peroxidase activity and isoenzyme pattern in

young flowering and in adult flowering trees

Introduction

1 year old and 30 year old trees of satsuma

mandarin were used to study seasonal changes

3 year old potted trees were used to study the

changes during low temperature flower induction

To study the effect of girdling, adult trees were

girdled by mid-September

Materials and Methods

Fractionation of enzyme activity

Results and discussion

Isoenzyme patterns of soluble and ionically bound cell wall peroxidases

Results and discussion

Changes in fresh weight of buds and leaves

Results and discussion

Changes in peroxidase activity in leaves

In adult trees, high peroxidase activities were mostly established by Sep. before the buds acquired competence to flower

Results and discussion

Isoenzyme patterns in leaves

Results and discussion

Results and discussion

Changes in peroxidase activity in buds

Results and discussion

Isoenzyme patterns in buds

Results and discussion

Effect of girdling on peroxidase activity

Results and discussion

Effect of inductive low temperature conditions

Higher peroxidase activities in the leaves from flowering trees compared to non-flowering trees could not be related to the flowering process

Consistent differences in peroxidase activity related to flowering was not found in the buds

Girdling had no effect on peroxidase activity

So, the enzyme fractions and the isoenzyme patterns are not useful markers for developmental flowering stages of the buds

Only one parameter was considered in this paper

Overview

Discussion