School of Agriculture,Policy and Development

EWRS conference , Santorini, September 2009 Novel and sustainable weed management in arid and semi-arid agro-ecosystems

Some implications of weed seed ecology for weed management

Alistair Murdoch

... Weeds are opportunists !!!

Photo by Dannie Romney, International Livestock Research Institute, Kenya

Prerequisites for invasive weeds

• Propagule dispersal to a new site during which…– Viability must be preserved– Growth must generally be prevented – Predation must be avoided

• After dispersal, invasion occurs if propagules can– Maintain viability– Prevent growth and– Avoid predation

until conditions are suitable for growth• Propagules must then be in the right physiological state to grow,

reproduce and disperse progeny.

http://www.filebuzz.com/software_screenshot/full/75438-Cartoon_Character_Screensaver.jpg

Watch out!We’ve got to stay alive

Preserving viabilitySeed storage behaviour

• Most weeds have ‘orthodox’ seed storage behaviour:– Seeds survive better when dried to very low moisture

contents and seeds can be frozen when dry

• Recalcitrant seeds:– Seeds cannot be dried without damage and some are

damaged by chilling below 15ºC

Loss of viability in dry storage

50°C, 80%rh

60°C, 75%rh

Phelipanche aegyptiaca

Kebr

eab

& M

urdo

ch (1

999)

W

eed

Rese

arch

10,

447

–457

Note seed to seed variationwithin population

Survival of Phelipanche/Orobanch

e seeds after dry

storage for up to

c. 400 days at various temper-

atures and moistures

Ph. aegyptiaca O. crenata O. minor

20°C

30°C

40°C

50°C

60°C

Ger

min

atio

n of

dry

sto

red

seed

s, %

Storage period, days

Kebreab & Murdoch (1999) Weed Research 10, 447–457

0

10

20

30

40

50

60

70

80

90

100

0 30 60 90 120 150 180 210

Conditioning period (days)

Ger

min

atio

n (%

)Phelipanche

aegyptiaca Orobanche cernua

O. crenata Survival of seeds after

wet storage for

up to 210 days at

30°C

Kebreab & Murdoch (1999) J Exp Bot 50: 211-219

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How long can you

live in soil?

Modelling seed depletion in soilNegative exponential decay curve

S = S0 e-gt or loge S = loge S0 - gt

where S is the number of surviving seeds from an initial population S0 after t years. g is the annual rate of depletion.

This model is only valid on– a year-to-year basis, and – in the absence of seed influx.

If true, implications include that seed banks have:– a constant half life, and – a constant annual probability of depletion

Predicting seed depletion Depletion factors

A depletion factor of 106 is likereducing the seed bank

from 1000 seeds/m2 to 10 seeds/ha.Elimination is therefore an unrealistic outcome for invasive plantmanagement unless the depletion rate is very high. Say > 90% per annum

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Don’t germinate all together

Germination prevention

• Dormancy• Quiescence

After-ripening period (days) at 40ºC, 43% rh

Open symbols: 32/27ºC, 13h/11h day/nightClosed symbols: 27/20ºC , 13h/11h day/night

Note seed to seed variationwithin population

Ger

min

atio

n pe

rcen

tage

(pro

babi

lity s

cale

)Seeddormancyvaries withmaturationconditionsCenchrusciliaris Sharif Zadeh & Murdoch Seed Science Research (2000) 10, 447–457

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Ger

min

atio

n, %

Afterripening period, days

20 C30 C40 C

50 C

60 C

Dormancy varies with post-harvest dry storage (afterripening), Striga hermonthica

After dry storage, seeds were pre-conditioned for 14 d in water at 30ºC and then germinated at 30ºC in 1ppm GR24. Seeds were collected in The Gambia from an infestation of millet.

Sonko & Murdoch, unpublished

To germinateor

not to germinatethat is the question

-

a balancing actfor the

individual seed –

How does this balance vary?

Collaborators and co-authors

• Laila Karlsson , Linköping, Sweden • Per Milberg, Linköping, Sweden • Paul Neve, Warwick, UK• Ilse A. Rasmussen, Flakkeberg, Denmark• Jukka Salonen, Jokioinen, Finland • Bozena Sera, Czech Republic• Edite Sousa, Tapada da Ajuda, Portugal • Francesco Tei, Perugia, Italy• Kirsten Tørresen, Ås, Norway • Jose M. Urbano, Sevilla, Spain

• Jose L. Gonzalez Andujar, Sevilla, Spain• Diane Benoit, Québec, Canada• Adam Davis, Urbana, IL, USA • Frank Forcella, Morris, MN, USA• Federica Graziani, Perugia, ITALY• Andrea Grundy, Warwick, UK

Regional variation of germination and dormancy of Chenopodium album seedlots tested at Reading as part of EWRS WG joint experiment. Seeds were obtained from most of those listed

0102030405060708090

35 40 45 50 55 60 65

Latitude, degrees North

Viab

ility

or n

on-d

orm

ancy

, an

gles

Viability (NS)

Non-dormancy (P<0.05)

General correlation of viability and “non-dormancy” of Chenopodium album with latitude of origin

Murdoch et al. unpublished

Optimum constant temperaturefor germination of Chenopodium albumis correlated with “non-dormancy”

10

14

18

22

26

30

0.0 20.0 40.0 60.0 80.0 100.0

Maximum germination on plate, %

Opt

imum

tem

pera

ture

, deg

C Spearmann Rank Correlation Coefficient:

-0.752 (P=0.005)

Optimum constant temperature for germination of Chenopodium album is NOT correlated with latitude of origin

10

14

18

22

26

30

35 40 45 50 55 60 65

Latitude, degrees North

Opt

imum

tem

pera

ture

, deg

C

Spearmann Rank Correlation Coefficient: -0.164 (P=0.56, NS)

Responses of common seed lot ofChenopodium album to 0.01 mol/Lpotassium nitrate in dark and light

0102030405060708090

Ger

min

atio

n, a

ngle

s

Common Seedlot Light

Dark

LSD

Water NitrateMurdoch et al. unpublished

Germination (angles) responses to KNO3 in darkness and light

Mur

doch

et a

l. un

publ

ished

Chenopodium album : Northern seed lots: additive effects of nitrate and lightSouthern seed lots: positive interaction (synergism)

-505

10152025303540

35 40 45 50 55 60 65

Latitude, degrees North

Inte

ract

ion,

ang

les

Interaction of lightand nitrate (P<0.05)

Canada

Murdoch et al. unpublished

Germination (º) after chilling for various periods

010

20304050

6070

0 10 20 30 40 50

Spain 37ºNegative slope

LSD (P =0.05)

010

20304050

6070

0 10 20 30 40 50

Portugal 38ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

USA-IL 40ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

Italy 43ºNegative slope

010

20304050

6070

0 10 20 30 40 50

Canada 45ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

USA-MN 45ºPositive slope

010

20304050

6070

0 10 20 30 40 50

Czech Rep. 48ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

UK 52ºNegative slope

010

20304050

6070

0 10 20 30 40 50

Common seed 55ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

Denmark 55ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

Norway 59ºSlope not significant

010

20304050

6070

0 10 20 30 40 50

Finland 60ºNegative slope

Chilling period, daysChilled at 3.1ºC; germinated at 10º/20º C (12h/12h) with light;means of 4 replicates of 50 seeds; SED = 4.4, 249 df

For the population of seeds: quantitative variation in behaviourin populations tends to be normally distributed.

Photo by Dannie Romney, International Livestock Research Institute, Kenya

Non-dorman

t

More light

please

Light AND nitrate AND

alternating temperatur

e

Chill out? I’m going back to

sleep

But there can be qualitative differences …

Nitrate please

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Don’t get suppressedby a crop

Suppression of biomass of different weeds (%)

Spring wheat cv Axona. 2002 growing season.

50

60

70

80

90

100

Vigour

Supp

ress

ion

of w

eed

biom

ass o

f ind

ivid

ual

spec

ies (

%)

low Medium High

Convo

lvulus

arve

nsis

LSD 7.

8 Anthe

mis cotu

laVio

la arv

ensis

LSD 3.

8Che

nopo

diu m

album

LSD

3.1Po

lygon

um sp

p.

LSD 4.

5So

lanum

nigru

m

LSD 3.

3

Sed df 29

50

60

70

80

90

100

50

60

70

80

90

100

Supp

ress

ion

of re

prod

uctiv

e un

its o

f ind

ivid

ual w

eed

spec

ies (%

)

low Medium High

Suppression of reproductive units (%)

Spring wheat cv Axona. 2002 growing season. Doukali unpublished

Convo

lvulus

arve

nsis

LSD 6.

3 Anthe

mis cotu

laVio

la arv

ensis

LSD 2.

8Che

nopo

diu m

album

LSD

3.3Po

lygon

um sp

p.

LSD 3.

8So

lanum

nigru

m

LSD 4.

0

0

10

20

30

40

50

0 100 250 400 550

Weed biomass suppression.Weeds suppressed similarly by high and low vigour crop seed lots if weeds emerged synchronously with crop. Effect of vigour eliminated at a given crop density.

() High vigour Asynchronous

() Low vigour Asynchronous

High () and low () vigour

synchronous

Crop density, plants / m2

Wee

d dr

y m

atte

r, g

per p

ot

Spring wheat cv Paragon. Unpublished results, Doukali and Murdoch 2006

0

5

10

15

20

25

0 100 250 400 550

Weed seed suppression.Seed production suppressed similarly by high and low vigour crop seed lots if weeds emerged synchronously with crop. Effect of vigour eliminated at a given crop density.

Spring wheat cv Paragon. Unpublished results, Doukali and Murdoch 2006

() High vigour Asynchronous

() Low vigour AsynchronousHigh () and

low () vigour

synchronous

Crop density, plants / m2

Wee

d se

eds,

g pe

r po

t

Some concluding outcomes for weed management

• Predicting population dynamics:– Quantify the life cycle– Quantify seed-to-seed variation in population

• Mitigate risk of sudden expansion of infestation– Explore options for control at various stages of the life cycle– Manage the crop to suppress weeds– Consider the overall farming system– Rarely find magic bullets!– Integrate diverse options is a best

• Have rational expectations of control of invasions– Understand factors affecting seed germination, dormancy and longevity

Watch out for new weed speciesTake your eyes off the ball and before you know it, a new

patch will have appeared.

Acknowledgements

Several research students contributed to this work– Farzad Sharifzadeh (Iran)– Landing Sonko (The Gambia)– Ermias Kebreab (Eritrea)– Musa Doukali (Libya)– Sophie Allen (UK)

EWRS Germination and Early Growth WG for seeds of Chenopodium album

Aren’t these strange flowers pretty? I’m going to take some home!

http://www.fhwa.dot.gov/environment/greenerroadsides/cartoon.gifUS fed highways administration