Reproductive succes of parasitic weeds in rice production...

Reproductive succes of parasitic weeds in rice production systems, affected by sowing date and host plant variety

Djoeke Langeloo

Supervisors: Lammert Bastiaans, Jonne Rodenburg, Aad van Ast

Examiner: Niels Anten

January 28, 2013

Overview

Introduction

Research question and hypotheses

Pot experiments

Materials and methods

Results

Field experiments

Materials and methods

Results

Conclusions and discussion

Introduction – Rice

Rice is the major food source in SSA

Most rapidly increasing food commodity

Important yield reducing factors are parasitic weeds

Introduction – Striga asiatica

Introduction – Striga asiatica

Introduction – R. fistulosa

Introduction – Rhamphicarpa fistulosa

Introduction – Occurrence parasitic weeds

Grazing area/ river

Introduction – weed control options

Biological control

(Hand) weeding

Fertilization

Herbicide application

(Inter)crop

Other varieties

Avoiding seed spread

Introduction – Problem

In recent years, farmers experienced more parasitic weeds

Farmers sow later in the year, because of delayed rainy season

Local rice varieties have long growth duration

Weed seed bank density has steadily increased

Research question

How do crop growth duration, sowing date and weed seed density affect the reproductive success of both S. asiatica and R. fistulosa?

Hypotheses

The two parasitic weed species will be affected and respond in a similar way

Later sowing and longer crop growth duration will both result in a higher seed capsule production

Both factors combined, have a multiplicative effect.

With increasing seed bank densities seed capsule production will level off due to intraspecific competition

The experiments

Two pot experiments

Two field experiments

Pot experiments – Set-up

Striga asiatica

Nine S. asiatica seed densities

With rice host variety IAC165

Rhamphicarpa fistulosa

Eight R. fistulosa seed densities

With and without rice host variety IR64

Observations:

Number of emerged weeds

Dry weight of emerged weeds

Plant height of R. fistulosa

Pot experiment – Results – S. asiatica

Very low S. asiatica emergence

< 0.07% of sown seeds

Results – R. fistulosa dry weight

a

bc

ab

cd

de

ef

f

a a ab ab abc abc abc

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

15 31 62 125 250 500 1000

Dry

we

igh

t o

f h

arve

ste

d R

ha

mp

hic

arp

a f

istu

losa

pla

nts

(g

po

t-1)

R. fistulosa sowing density (# of seeds pot-1)

Rhamphicarpa with rice Rhamphicarpa alone

Results – R. fistulosa plant height

0

2

4

6

8

10

12

14

16

15 31 62 125 250 500 1000

Ave

rage

he

igh

t o

f R

ha

mp

hic

arp

a f

istu

losa

pla

nts

(cm

po

t-1)

R. fistulosa sowing density (# of seeds pot-1)

Rhamphicarpa with rice (b) Rhamphicarpa alone (a)

Field experiments – Set-up

Three susceptible rice varieties per weed

S. asiatica: Super India, Mwangulu and NERICA-14

R. fistulosa: Super India, IR64 and NERICA-L-20

Five sowing dates – biweekly sowing

Late-December till mid-February

Observations:

Biweekly: number of emerged, flowering and capsule bearing weeds

Final number of weeds and capsules

Final dry weight of weeds and capsules

Results – S. asiatica emergence N

um

ber

of

emer

ged

Str

iga

asi

ati

ca p

lan

ts m

-2

Nu

mb

er o

f em

erge

d S

trig

a a

sia

tica

pla

nts

m-2

R

ain

(m

m)

S = Sowing time, V = Variety

V1: Super India V2: Mwangulu V3: NERICA-14

Results – Number of harvested S. asiatica plants

V1: Super India V2: Mwangulu V3: NERICA-14

b

a a

ab

a

0

2

4

6

8

10

12

14

16

V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3

S1 S2 S3 S4 S5

Nu

mb

er

of

har

vest

ed

Str

iga

asi

ati

ca p

lan

ts (

# m

-2)

Results – Number of produced S. asiatica seed capsules

V1: Super India V2: Mwangulu V3: NERICA-14

c

b

a

bc

b

0

10

20

30

40

50

60

70

80

90

V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3

S1 S2 S3 S4 S5

Nu

mb

er

of

pro

du

ced

Str

iga

asi

ati

ca s

ee

d c

apsu

les

(# m

-2)

No variety effect

Results – R. fistulosa emergence S = Sowing time, V = Variety

V1: Super India V2: IR64 V3: NERICA-L-20

Results – Number of harvested R. fistulosa plants

V1: Super India V2: IR64 V3: NERICA-L-20

0

10

20

30

40

50

60

70

80

V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 alone

S1 S2 S3 S4 S5 Rh

Har

vest

ed

nu

mb

er

of

Rh

am

ph

ica

rpa

fis

tulo

sa p

lan

ts (

#m-2

)

bc

cd

d

a

ab

Results – Number of produced R. fistulosa seed capsules

V1: Super India V2: IR64 V3: NERICA-L-20

a a a a a ab ab a ab

cd

bc

c

c

e

d

0

50

100

150

200

250

300

V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 V1 V2 V3 alone

S1 S2 S3 S4 S5 Rh

Nu

mb

er

of

pro

du

ced

Rh

am

ph

ica

rpa

fis

tulo

sa s

ee

d c

apsu

les

m-2

Last sowing date:

Variety effect

Results – Crop growth duration

V1: Super India V2: IR64 V3: NERICA-L-20

0

20

40

60

80

100

120

140

160

180

S1 S2 S3 S4 S5 S1 S2 S3 S4 S5 S1 S2 S3 S4 S5

V1 V2 V3

Nu

mb

er

of

day

s b

etw

ee

n s

ow

ing

and

har

vest

of

cro

p (

day

s)

Discussion and Conclusion – 1

Farmers observations regarding increased weed pressure with later sowing time were confirmed for R. fistulosa

For both weeds a clear effect of sowing time was found

Early sowing of rice resulted in most S. asiatica seed capsules

Late sowing or rice resulted in most R. fistulosa seed capsules

The found variety effect was less clear

For S. asiatica no variety effect was found

For R. fistulosa differences were found between varieties in latest sowing date

Time

Rainfall

S. asiatica seed conditioning

Excretion of germination stimulants

Rice germination and emergence

Large S. asiatica emergence

Early rice sowing

Time

Rainfall

S. asiatica seed conditioning

Early rice sowing

Excretion of germination stimulants

Rice germination and emergence

Large S. asiatica emergence

Time

Rainfall

S. asiatica seed conditioning

Late rice sowing

Excretion of germination stimulants

Rice germination and emergence

Little S. asiatica emergence

Some S. asiatica seed become dormant again

Time

Rainfall

R. fistulosa emergence

Rice emergence

Little R. fistulosa plants and seed

capsule production

Drought

R. fistulosa dries and dies

Rainfall

R. fistulosa germination

At rice harvest Early rice sowing

Time

Rainfall

R. fistulosa emergence

Late rice sowing

Rice emergence A lot R. fistulosa

plants and seed capsule production

Drought

R. fistulosa dries and dies

Rainfall

R. fistulosa germination

At rice harvest

Time

Rainfall

R. fistulosa emergence

Early rice sowing

Rice emergence

Little R. fistulosa plants and seed

capsule production

Drought

R. fistulosa dries and dies

Rainfall

R. fistulosa germination

At rice harvest

Discussion and Conclusion – 3

S. asiatica

Water to break dormancy

Without host root exudates seed turn to secondary dormancy

Rice sowing as late as possible after the February drought

R. fistulosa

Water to survive

Rice sowing before the February drought

So early drought can reduce R. fistulosa presence

Can de-synchronisation be used as a management tool?

Thank you for your attention!

Questions?