Theoretical Module

Phenology :- Phenological phases of annual crops- Thermal time- Photoperiodism

M. Dingkuhn

Phenology

Development (differentiation) ≠ Growth

Juvenile phase

BVP

PSP Reproductive phase Maturation

PI Fl Mat

Vegetative phase

Differentiation ofinflorescence

Grain fillingProduction of leaves and tillers

Germination

Cycle

Development = temporal organisation of organogenesis (structure)

Vegetative phase

Reproductive phase

Grain filling phase

PSPjuvénile

Basic concepts (1)

• Thermal time (TT, in degree-days)

• TT accumulation, TT-budgets per phase• Progress towards X = TT(day i) / TT(budget)• X = end of BVP, PI, flowering, matutity

Tb To(1) To(2) Tm (=Tlim)

Rate

Basic concepts (2)

• Floral induction• Photoperiod sensitivity (PP) and PSP• Plants ‘SDP’ or ‘LDP’

• Un inhibition or une induction of flowering?– Concept of induction: accumulation of a signal 1/(PPact-PPcrit)

– Concept of inhibition: Perception of a critical day length

• Qualitative (gradual) and quantative (absolute) responses

Quantitative vs qualitative response

Linear or exponential responseTT-budget = constant or dynamic

Duration of PSP in C.d

Day length (h)

Photoperiod sensitivity confers adaptation, especially to wet-season upland crops:

25-05 15-07 25-09Variation of start of wet season

End of wet season

PP-sensitive

PP-insensitive

Need to plant upon 1st major rains:- «Flush» of N, then loss by leaching- Weed flora

Need to flower at end of wet season:- Grain diseases- Terminal drought- Higher solar radiation- Regional crop synchronization to minimize bird damage

« true » onset of monssoon

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23-M ar 21-J un 19-S ep 18-D ec

S eed lin g d ate

The

rmal

tim

e (°

C.d

ay)

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23-M ar 21-J un 19-S ep 18-D ec

a) S ee d ling - P I

b ) P I - f lag le a f

c ) F la g lea f - flo w e ring

C S M 335

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S ariaso 10

IR A T 174

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Variability of duration of phenologigal phases

(sorghum sowing date experiments in Mali)

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Tem

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ture

s (°

C)

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Ave

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%)

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Civ

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ylen

gth

(h)

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-25

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il da

ylen

gth

rate

of

chan

ge (

s.da

y-1)

a )

b )

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d )

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GR

(M

J/m

²)

e )

Problem of auto-correlation among climate variables

Phenology, from a biological perspective: Meristems

• Linear succession of phytomer generation (organogenesis)

• Phytomer = leaf + sheath + node + internode + tiller bud + adv. root

• Plastochron, Phyllochron = sequential duplication

• Tillering = lateral duplication

• Floral initiation changes meristem behavior

• PI and internode elongation usually coincide with onset of secondary phyllochron (slower)

• Organ metamorphoses (e.g., anthers are leaves)

• Meristem = site of expression of genes for development

Dissection for apex diagnostics (Lane, 1964)

0 1 2 3 4

CSM 335

y = 0.0244x + 1.1562R2 = 0.9846

y = 0.0298x + 4.0644R2 = 0.9811

y = 0.0112x + 10.286R2 = 0.9632

y = 0.0117x + 15.838R2 = 0.9682

0

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Thermal time from seedling (°C.day)

Num

ber

of le

ave

s

Initiated Appeared

Sorghum: primary and secondary plastochron and phyllochron

Development of canopy height (top) and stem length(ground to meristem, bottom) for sorghumcv. CSM 335, sown on 26 con-secutive months , 2000-2002, Bamako.

= June & July crops

22 = tot. leaf number.

= panicle initiation.

Sorghum: Variability of Canopy Height and Leaf number

Many models of photoperiodism• Classical models (accumulation of fn(PP, T)

• Quantitative models (linear or mildly exponential)• Qualitative models (strongly exponential)

• Dynamic model: accumulation of fn(delta-PP)• Models inspired by A. thaliana (circadians pathway interacting with

T-pathway)• Model by Folliard et al. (2004) : variable day leng th threshold• => Impatience (Dingkuhn net al., 2008): Threshold lo wering

under prolonged appetence

Standard in SAMARA crop model

RIDEV V2: choice of Impatience, linear, exponential , dynamic

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Average photoperiod during PSP (h)

The

rmal

dur

atio

n of

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P (

°C.d

ay, b

11)

a)

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b)

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Photoperiod at panicle initiation (h:mn)

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rmal

dur

atio

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P (

°C.d

ay, b

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c)

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d)

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Thermal durationof PSP vs meanPP during PSP fortwo sorghum cvs.for 12 sowingdates (months) atBamako, Mali.

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Pho

tope

riod

(h:m

n)

a)

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Weeks after plants emergence

b)

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c)

Evidence for dynamic model: Different effects of increasing or decreasing day length on PI of 3 sorghum cvs. in growth chambers. Lines end where PI was observed

CSM 335 Sariaso 10 IRAT 174

Sariaso 10CSM 335

sowing dates inwet season

cv. Souroukoukou

Date of sowing

1/1/20041/2/20041/3/20041/4/20041/5/20041/6/20041/7/20041/8/20041/9/20041/10/20041/11/20041/12/2004

Dur

atio

n so

win

g to

PI (

days

)

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Observed (Sotuba/Bamako, 2004)Simulated with present model: PPcrit1=12h, PPcrit2=13.5h, PPexp=0.2, threshold=0.6 Simulated (Folliard et al., 2004)

Principle :With increasing duration of PSP (appetence), the plant is satisfied with a lesser signal (longer days)

Adaptation in SAMARA and RIDEVVarTEST = (1000 / TsumPSP) ^ PPexp * (PPact - PPcrit) / (SeuilPP - PPcrit)

Example :VarTEST = (1000 / TsumPSP) ^ 0.2 * (MAX(PPact,12) -12) / (13.5-12)

Decision criterion for floral initiation:If VarTEST < PPsens then PI

This model givesthe same results asthe Folliard model

IMPATIENCE model adopted for cereals

Sensitivity analysis of IMPATENCE to parameter PPsens

Non-linear model (PPexp = 0.2)

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n da

te

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th

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PI (threshold 0.4)PI (threshold 1.0)PI (threshold 1.4)Sowing

PPcrit1 = 12.0hPPcrit2 = 13.5hPPexp = 0.2

PI thresholdparameter:

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Dur

atio

n of

PS

P (

°C.d

)

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1.41.21.00.80.60.4

Non-linear model

Duration of PSP vs. sowing date Date of end-of-BVP and of PIvs. sowing date

Month Month

S o w in g d a te

01/01/0

201/0

2/02

01/03/0

201/0

4/02

01/05/0

201/0

6/02

01/07/0

201/0

8/02

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201/1

0/02

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201/1

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3

Dur

atio

n of

PS

P (

degr

ee-d

ays)

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5 0 0

1 0 0 0

1 5 0 0

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2 5 0 0

3 0 0 0B la n c A u gIS 1 5 4 0 1K a u r a D - 1 2S h o r t K a u r aF a r a fa r a 1 7C S 0 2 M a d a g a s c a rC G M 1 9K e n d é N b e B laIR A T 2 0 4S a r ia s o 1 0S o u r o u k o u k o u

a

Observations :Clerget et al.

Model PPcrit1 = 12.0hPPcrit2 = 13.5hPPexp = 0.2

PI thresholdparameter:

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Dur

atio

n of

PS

P (

°C.d

)

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1.41.21.00.80.60.4

Non-linear model

10

Julian date (2004)

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Model test variable for PI

0.0

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2.0

2.5

End of BVPObserved panicleinitiation

Equ

inox

Increasing daylength Decreasing daylength

No PI

Model threshold for PI

Thermal time elapsed since end of BVP (°C.d)

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Day length at end of BVP and PI (h)

12.0

12.5

13.0

13.5

Dynamic day length threshold according to modelObserved PIObserved end of BVP

15/08

15/07

15/0615/05

15/04

15/03

15/02

15/0115/09

Sowing date15/10/2004

Decreasingday length

Increasing day length

a b

V1-2004

Julian day

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Day

s af

ter

sow

ing

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V2-2004

Julian day

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V3-2004

Julian day

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Calibration

Validation

(Dingkuhn et al., 2008)

2005 Validation (a)

Julian day

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Day

s af

ter

sow

ing

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V1, observedsimulatedV2, observedsimulatedV3, observedsimulated

2005 Validation (b)

Observed duration (d)

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Sim

ulat

ed

dur

atio

n (d

)

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V1V2V3

Flowering:Y = 14.6 + 0.793X, R² = 0.98

Panicle initiation:Y = 4.46 + 0.883X, R² = 0.98

(MERCI)