Root as a Trait for Improving Crop Productivity-presentation

8/3/2019 Root as a Trait for Improving Crop Productivity-presentation

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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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Root as a Trait for Improving Crop Productivity-presentation

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