Characteristics and control of

shoot growth and flowering in

citrus

L. G. Albrigo

Citrus Research and Education Center

General shoot and flower growth

• Spring or rainy season

– Shoot sprouting and flower development

• Later in warm season

– Additional shoot sprouting

• Bearing trees – Two to three sprouting

cycles

• Young non-bearing trees – Four or 5

growth flushes

General control of growth

• Tree physiology and health

– Tree age – Juvenility

– Bud age – maturation

– Tree vigor – nutrition, health (internal stress)

– Source-sink competition - crop load, root/shoot

growth cycles

• Climate

– Water for growth, drought for inducing flowers

– Temperature, moderate to high for growth, cool

temperatures for inducing flowers

Major Climate Types in Which Citrus is Grown

• Mediterranean Subtropical– Cold Winters, hot Summers, low rainfall

– Spain, California

• Humid Subtropical (Intermediate Climates)– Cool Winters, warm Summers, high rainfall

– Florida, Brazil, Some of Mexico, tropical highlands

• Dry Intermediate –– Peru, some of Mexico

• Tropical– Warm to hot weather all year

– Columbia lowlands, Venezuela, Peru, Ecuador, Yucatan-Mexico

In tropical and intermediate climates,

after diseases, flowering is usually the

most important reproductive factor in

determining yield

• Mediterranean climates often result in

excessive flowering

• Flowering intensity and frequency are

very important in intermediate climates

such as Florida and Mexico

• In Tropical climates flowering usually

insufficient (parts of Mexico?)

Early events in vegetative

growth of citrus

• Bud and leaf age maturation requirement

– Two months ?

• Bud break

Weather effects on growth

• Threshold temperature for vegetative

growth – 13 o C

• In tropical climates available soil

moisture is usually threshold factor for

growth

• In intermediate climates both

temperature and soil moisture may play a

role in initiation of growth

Early Events in Reproductive Growth

of Citrus

• Flower bud induction

• Initiation of growth of flower buds

• Differentiation of flower buds

• Flowering

– Anthesis

Internal factors in flowering

• Leaf and bud maturation

– Capable of receiving and translating

environmental stimulus

• Upregulation of flowering genes

– Leaf to bud and bud sequence

Flowering response of different

aged shoots

Shoot

age

Total

buds

New

shoots #

Flower

shoots #

Flowers

%

4 weeks 722 155 2 1.2

6 weeks 583 167 32 19.2

8 weeks 537 139 83 59.7

10 weeks 390 166 113 68.1

Vegetative flush

on 4 to 6 week

old shoots, no

flower induction

Flowering on 8

week old shoots

4 wks induction

Factors Involved with Flower Bud

Induction

• Temperature

– Required temperature

– Duration

• Drought

– Soil Moisture (Rainfall)

– Level of drought

– Duration

• Crop load

• Growth Regulation

Effect of Winter on Flowering of

Citrus in Israel

0

10

20

30

40

50

60

70

Nov Dec Jan

Control

%

F

l

o

w

e

r

i

n

g

Ayalon and Monselise, 1957

Typical Change in Flowering Intensity

through Winter

Moss

Australia

Value of Cooler Temperatures on

Flower Bud Induction

Temperatures below 20 o C (68 o F) induce flower buds

Moss

Australia

Value of Cool Temperatures on Flower

Bud Induction

Temperatures below 18 o C (64 o F) accelerate flowering response

Effect of Increasing Time Trees Held

at Inductive Temperature

Total shoots

Flowering Moss

Australia

Water Stress Induced Flower Buds

• Tropics – dry spells followed by rainy

season (Often two or more blooms/year)

• Require about 60 days of water stress for

oranges, longer periods (> 70 days)

detrimental to plant (Cassin et al > Tropics)

• Require more than 45 days for Persian

lime to have economic bloom (Borotto et al, >

Cuba)

Under tropics, several blooms:

Difficult to evaluate cropping

levels & interactions of

different fruit sets

Shoot Age &

Sprouting

Summer

Spring

Guardiola et al > Spain

Florida, Summer shoots > more sprouts & flowers

Valiente

and

Albrigo,

2004

80 % of

flowers

from 1st

four buds

INDUCTION

HOURS FOR 20

YEARS

REPORTED TO

HAVE SINGLE

BLOOMS IN

FLORIDA

Valiente and

Albrigo

RANGE OF HOURS

712 TO 1590 Average = 900 to 1000

60-61 27-Dec 1020

62-63 17-Dec 1129

65-66 1-Jan 1234

66-67 1-Jan 1316

68-69 10-Jan 1474

70-71 4-Jan 1257

72-73 30-Dec 1054

75-76 25-Dec 961

76-77 10-Dec 1034

77-78 14-Dec 936

78-79 7-Jan 1092

79-80 10-Jan 1304

81-82 23-Dec 1093

83-84 29-Dec 1052

84-85 14-Dec 1023

85-86 6-Jan 990

87-88 21-Dec 1084

88-89 21-Dec 1047

90-91 16-Dec 712

99-00 1-Jan 1131

00-01 8-Jan 1590

Induction hours

below 20 CInitiation DateYear

Flowers/shoot by Bud Position as

Winter Progresses – Florida - Valencia

Apex

Different

flowering

levels in

2 years

Mediterranean Vs. Florida Weather

Extended period below 20 o C (68 o F) versus many hours above 25 o C (77 o F)

• Greater variability among years

• Greater range of temperature fluctuations

Florida Weather

Many Intermediate Climates Have

Both Low Temperature & Water

Stress Induction of Flower Buds

• Florida does not have long enough dry periods

• Mexico – some areas probably do have both

• Requires some Winter rains on cold fronts

• Brazil is good example of both factors playing a role depending on year

Fruit/tree

ranking

Year Days of

Drought

Days of cool

temperatures

Total days of

Drought and cool T

1 1998 55 40 95

2 2001 40 – 78 31 90

3 1995 40 – 60 20 70 - 80

4 1999 25 72 97

5 1996 48 46 94

6 1997 40 20 60

7 2000 80 28?* 108?* All drought?

8 2002 44 14 58

Yield Ranking and Days of Drought or Low Temps

Southern Sao Paulo State, Brazil

(108)

Very

low

years

Use of urea to enhance flowering

intensity

Effect of Urea Sprays on Flowering of

Citrus

0

10

20

30

40

50

60

70

Nov Dec Jan

Control

Urea Spray

%

F

l

o

w

e

r

i

n

g

Ayalon and Monselise, 1957

Temperature and urea increase leaf ammonia-ium levels with

corresponding increases in flowers per tree. (Lovatt, Calif.)

Winter Low Temperature and Urea

Spray Increase Flowering

Water stress alone and with urea increase leaf ammonia-ium levels and flowers

per tree. Moderate stress with urea best combination. (Lovatt, Calif.)

Water Stress & Urea Increase

Flowering

VALENCIA - 1994-95

South Florida

0

500

1000

1500

2000

2500

FLOWERS YIELD

CONTROL

UREA

NUTRIPHITE

a

a

ab b

FRUITLETS

a

b

b

Albrigo, Florida

VALENCIA – YIELDS, 4 SEASONS

South FloridaTREAT-

MENT

YEAR 1 YEAR 2 YEAR 3 YEAR 4 TOTAL

CONTROL 1193

483

892

361

1000

405

823

333

978

396 aUREA 1289

522

921

373

1107

448

981

397

1074

435 bNUTRI-

PHITE1442

584

968

392

1158

469

1030

417

1150

466 b

BOXES PER HECTARE OR PER ACRE

Numerical increase every year

Table 2. Winter timing of urea sprays on

flowers per bud on spring or summer shoots

2.6 c2.4 c2.5 c2.7 cbSPRING

3.4 a3.5 a3.2 ab3.0 bSUMMER

UREA

SPRAY 18/1

UREA

SPRAY 5/1

UREA

SPRAY

31/12

CONTROLSHOOT

AGE

Summer shoots affected (main flowering unit).

Timing of winter urea dependent on year. Need

induction, but before differentiation has

progressed. (Frost & Albrigo, Florida)

Flowering of

Mandarin under

Mediterranean

conditions

Note many

flowers and a

few small leaves

Heavy flowering in Florida conditions

More flowers = More fruit (use urea)

until excess flowers then use GA3

Accumulating

winter cool

temperatures

GA EFFECT- 20ppm

Guardiola et al, Spain

Flower Development

• Initiation of flower bud development

– Warm weather

– adequate soil moisture for growth

• Flower Bud differentiation

– Development of flower and leaf parts

• Flower bud growth (Inflorescence)

• Bloom (Anthesis)

Effect of Florida Winter Weather on

Initiation(s) of Flower Bud Differentiation

• Winter warm spells result in bud growth if induced to flower– Multiple blooms occur if cool period between warm

periods

– If the mid-bloom dates are less than 4 weeks apart• overlap and perceived as prolonged bloom

– Less than 2-3 weeks apart, usually not perceived

• Warm spells = reduced intensity of bloom waves

• Multiple blooms increase scheduling problems –– Disease control, harvesting

• In Florida – multiple blooms in Spring are usual

Factors Involved in Initiation of

Flower Bud Differentiation

• Induction levels

• Temperature

– Warm periods

• Soil Moisture

– Adequate for growth

• 1 to 2 MPa will inhibit growth

• 2 to 3 MPa required to promote flower bud

induction and need at least 30 to 40 days

Florida Winters and Warm Spells

One bloom versus four or more in 1998-99

Environmental factors involved in

flower bud differentiation

• Temperature

– Higher temperatures up to 21 o C accelerate

development

– In excess of 25 o C may cause flower drop

• Soil Moisture

– Adequate for growth

Predicting date of bloom - Florida

• Temperature model

Parameter Variable Estimate F Value R2= 0.9439

Intercept 6.40436 2.05 DD Below 12.8 0.13267 123.98DD 12.8 to 20.8 0.27848 106.64 DD Above 20.8 -0.35277 37.61

Valiente & Albrigo, 2000

Flower Bud Differentiation Time

as a Function of Degree-days

Florida, over

20 years

55 to 85 days

to bloom

from

initiation

Tropics 24

days

Med.

Subtropics 90

to 120 days

Mean weekly temperatures during

flower bud development for five

recent years

Integrating Information into a Predictive

System – Florida Citrus Industry

• Flowering intensity

• Flowering waves

• Dates of bloom

• Recommendations for altering bloom

• Citrus Flowering Expert System

– Citrus flowering monitor system

Goals

‘Citrus Flowering Monitor System’

PRIMARY• Monitor the level of flower bud induction

– Use as a decision making tool

• Determine if initiation of flower bud

differentiation has occurred (Warm

periods)

• Predict bloom date(s) for production

practices scheduling

Goals (continued)

‘Citrus Flowering Monitor System’

• Determine the level of flower bud induction

– Flowering intensity progress, level at time of warm

period

– Monitor warm weather events that disrupt

induction and start differentiation (initiation)

• Provide recommendations (management

strategies) and their timing

– 1) minimize the effect of early winter warm events

• If and when to apply water stress

• If and when to apply GA or urea

Data sources for Expert System

• Uses weather station system

• Uses NOAA weather predictions (8 days)

• Graphs cool temperature accumulation

• Identifies warm periods

• Predicts bloom

Flower bud

and flower

development

Induction level

progressWarm event

5-7 day period

2000-01

results

First

initiation

2001-2002

year’s

initiation

840 hours versus

640 previous year

250 million boxes vs

200 million boxes

Mean monthly temperatures 2014-2015 winter

Hermosillo, Sonora

Winter inductive hours,

Hermosillo, Sonora

Month/year 2012-13 2013-14 2014-15 2015-16

November 144 0 0 288

December 480 360 288 598

January 551 240 288 495

Total hrs <

19

1175 600 576 1381

Two of four years short of inductive years due to warm

Novembers. Drought period needed to compensate?

Take home message for

Hermosillo• Some years may not have enough cool

temperature induction

• Appears November is critical

• November drought stress may be needed

• An ultralow volume drip irrigation

scheme was developed in Brazil (Albrigo

and Carerra, 2012) to produce drought

induction without severe drought stress

Thank you