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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?
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