Transcript Why is early weed control important in corn?

Role of Seed Treatments
in Plant Competition
Clarence Swanton
University of Guelph
Aspects of competition
(Bosnic and Swanton, 1997)
Yield (% of weed-free)
100
80
60
Time of weed emergence
4 leaf
1 leaf
0
0
25
50
75
100
125
150
Weed density (plants per m of row)
Crop-weed competition
Can corn seedlings



Detect their
environment?
Adjust quickly to
environmental
changes?
Communicate with
weeds?
Photo: P. Smith
Shade Avoidance
Light quality can be measured as R/FR
Low R/FR light induces a shade avoidance response
0.20
0.18
1.4
a
Anthocyanin
Lignin
b
0.16
0.14
b
b
1.2
b
1.0
a
0.12
0.8
0.10
0.6
0.08
0.06
0.4
0.04
0.2
0.02
0.00
0.0
WF
W
FRF
Lignin content (OD @ 415)
Anthocyanins content (OD@530-OD@567)
Shade avoidance decreased anthocyanin and
increased lignin content in stem tissue
Anthocyanin’s act as:
1) sunscreen for leaves
2) powerful antioxidants
Shade avoidance increased ethylene
biosynthesis gene expression
Shade avoidance up-regulated the
auxin transporter gene
Reactive Oxygen Species
•Are chemically reactive molecules containing
oxygen. Examples include oxygen ions and
peroxidases (H2O2)
•Naturally found in cells as a by product of oxygen
metabolism
•Play an important role in cell signalling and
homeostasis (maintenance of physiological stability)
•Environmental stress causes ROS levels to
increase dramatically
Oxidative damage caused by reactive
oxygen species (e.g.H2O2) include:
• Damage DNA
• Damage proteins and lipids
• Inactivation of enzymes
• Alteration of plant metabolism
• Stomatal closure
Shade avoidance increased H2O2 content in
corn seedlings
0.18
0.16
0.14
H2O2 Content (nM)
First leaf
Second leaf
Stem
c
a
0.12
a
b
a
a
0.10
0.08
a
0.06
a
a
0.04
a
0.02
0.00
WF
W
FRF
WF
W
FRF
Shade avoidance caused 3 times the amount
of stomatal closure in corn seedlings
Weed-free
Weedy
FRF
Thiamethoxam is a broad-spectrum
neonictinoid insecticide
• Seed treatment sold as Cruiser ® ,
Syngenta
• Distributed systemically throughout the
plant
We know the R:FR reflected from the leaf
surface of weeds
• Anthocyanins
• H2O2
Treatments:
1) Weed-free – untreated
2) Weed-free – seed treated
3) Weedy – untreated
4) Weedy – seed treated
Experiment replicated 5 times
Thiamethoxam increased percent
germination and length of root radicle
Corn seedlings originating from seeds
treated with thiamethoxam did not
express typical morphological shade
avoidance responses when exposed to
above-ground neighbouring weeds
Seed Treatment
Weed-Free
Weedy
No Seed Treatment
Weed-Free
Weedy
Influence of thiamethoxam on corn height
at the 4th leaf tip stage
Phenotypic
parameters
Second leaf collar
height (cm)
Treatment
UN-WF
UN-W
T-WF
T-W
8.6 a
9.9 b
8.9 a
8.8 a
Thiamethoxam as a seed treatment prevented the loss of
anthocyanin caused by neighbouring weeds
Corn seedlings originating from seeds
treated with thiamethoxam accumulated
less H2O2 when exposed to above-ground
neighbouring weeds
Summary:
Under non-limiting resource conditions
thiamethoxam
• Enhanced seed germination
• Negated the anticipated morphological shade
avoidance response
• Maintained anthocyanin content
• Activated antioxidant systems that reduced
accumulation of H2O2
• Seed treatments a component of
Integrated Weed Management
• Agronomic implications- stress & ROS
• Role of seed treatments go beyond crop
protection to include targeted gene
activation for stress tolerance
Acknowledgements
Thank you