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ROOT AS A TRAIT FOR IMPROVING CROP
PRODUCTIVITY
KABEYA J. MUAMBA
I PhD, CROP PHYSIOLOGY
PAL-0036
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Introduction
Root study has an array of importance to crop productivity and can contribute to anyield enhancement in agricultural crops, aside its main roles in simplicity such as,
Water uptake
Nutrients absorption
Plant anchorage
Some years back, Scientists mainly focused on increasing shoot biomass and
seed yield while neglecting or overlooked the relevance of root system for food
production.
The world is facing the major challenge of providing food security for an ever
growing world population,(Godfray, H.C. et al., 2010)
There is a need to look for an alternative approach, rather than the green
revolution, to cope with threatening food shoratge
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And consequently, central for the plant to reach optimal growth and is sure to
contribute to the levels of yield obtained in crops.
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A better understanding of the basic mechanisms of root growth and
development is very crucial
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Root System Architecture (RSA) is highly plastic trait
The primary root is formed during embryogenesis
Lateral Roots are derived post-embryonically from thepericycle tissue
Adventitious roots originating from shoot structures
Root hairs. extensions of epidermal cells
Molecular mechanisms of RSA are poorly understood. However,
number of mutant studies in model plants start to address this
issue.
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Primary root
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Asymmetric cell
divisions Leads todiversity of cell
types
hypophysis
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Rice Root Development as model for monocots
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A schematic representation of radicle
transverse organization
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In rice roots, all tissues originate from the RAM, which is
composed of three histogens,
A calyptrogen (root cap),
A dermatogenperiblem complex (all tissues from epidermisto endodermis), and
A plerome (stele tissues) surrounding a putative
Rice RAM belongs to the closed meristem type, with structural
initial layers arranged in three tiers.
1. First tier made up of the peripheral root cap and columella
initial cells, produces the root cap and columella.
2. second tier is made up of epidermisendodermis initial
cells.3. Finally, the last tier is made up of stele initial cells.
The QC size in the RAMs of the four rice root types and in
crown roots of different diameters probably differs.
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Organization of tissues and a model for cell division in rice root.
(a) Median longitudinal section of root tip.
(b) Division patterns of the initials that allow re-establishment of identically
grouped initials and derivatives, which can form all different tissue layers,
are depicted as broken lines.
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longitudinal view of a small lateral root
The same pattern as described for the radicle meristem is observed:
Periclinal divisions for columella initials (red arrows),
Anticlinal divisions for peripheral root cap initials (white arrows)
Three sequential periclinal divisions occur, giving rise to epidermis,
exodermis, sclerenchyma, and endodermis (yellow arrows).
cc - central cells;
en - endodermis;
pe - pericycle;
sc - sclerenchyma layer;
ex - exodermis;
ep - epidermis.
Scale bar 50 m
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In O. sativa, significant genetic variation has been observed in
root number, diameter, depth, branching, vertical density
distribution, r/s ratio, water extraction, and root penetration(OToole and Bland 1987; Lafitte et al. 2001).
The pattern of variation reflects the organization of O. sativa in six isozymic groups
as described by Glaszmann (1987).
The major differentiation is between isozymic group 1 (indicas), isozymic group 6 (japonicas)
Isozymic group 1 (indicas), Isozymic group 6 (japonicas)
A superficial thin root system a deep, thick, root system
Highly branched root system less branched root systemWith a low R/S ratio with a high R/S ratio.
Most of the diversity is distributed between groups rather than within groups,
(Courtois et al. 1996; Lafitte et al. 2001).
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Apart from the inherent genetic potential, soil as a medium of growth
can have propound impact on the root architecture
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Root anatomical adaptations also can play a crucial
role in imparting drought tolerance
Submerged roots
Aerenchyma and air spaces
Irrigated condition
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Cross sections of root cylinder of rice
Submergence
Irrigated
Methyl green and
Kongo red
Methyl green
Methyl green and
Kongo red
Kongo red
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Measuring root traits
Destructive Non-destructive
Hydroponics Agar plates
Rhizotrons + growth mapping
Mini- or micro-rhizotrons
+ image collection systems Root mapping on soil columns
Three-dimensional imaging
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Agar as medium
Hydroponics
Problems:
Algae grow wild
Requires really homogeneous greenhouse
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J.-L. Drouet et al. / Europ. J. Agronomy 22 (2005) 185
193
Rhizotrons + growth mapping
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Mini- or micro-rhizotrons + image collection systems
wric.ucdavis.edu/yst/ biology/biology-growth1.html
It consists of a rotating linear scan head, a notebookcomputer and clear Plexiglas tubes.
To obtain an image, insert the scan head into the
tube,start the scanning program on the computer.
The scan head will automatically rotate a full circle
creating a full circle (21.59 19.56 cm) image of the
soil and roots.
The scanned color image is displayed on the laptopscreen as it is created.
The images can be analyzed by varieties of software.
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Root growth mapping on soil columns
Giuliani et al., unpublished
Example of roots mapping outside a transparent soil
column in black: roots at 12 DAP; in blue at 23 DAP;
in red at 30DAP; in green-purple 38DAP
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X-ray CT features
resolution of about 100 m
short scanning time
low radiation dose
system relatively inexpensive (20 000) compared with
other tomographic systems
Computer Tomography (CT) based on:
1. X-ray
2. Nuclear Magnetic Resonance
3. g-ray
Gregory et al., 2003
Three-dimensional imaging
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Light-transmission
Light transmission imaging of
root water uptake in
transparent rhizotrons.
The lighter the shade of grey,the drier the soil (field of view
~50 100 cm).
Pierret et al., 2003
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X-ray
Lupin 1-cm thick, 50 25 cm rhizotron
Rhizotron filled with a sandy
loam soil homogeneously packed
X-ray imaging of live root systems in
rhizotrons: series of images taken at weeklyinterval demonstrating the technique
potential for monitoring root growth.
Pierret et al., 2003
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Measuring root traits
Destructive
method
Non-destructive
method
Excavation
Core-break
Direct observation
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Excavation
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Counting the number of roots that project from the 2
broken surfaces of a soil core in the core-break technique
Core-break technique
Taylor et al., 1991
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