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IMPROVING SALT TOLERANCE OF WHEAT
Rana Munns CSIRO Plant Industry, and
University of Western Australia
The food demand gap
Environmental Issues
Salinity Biotic stress
Drought Loss of biodiversity
Outline of talk
• Two types of dryland salinity in Australia
• How native plants evolved to deal with it
• How agriculture deals with it, through plant
physiology, genetics and plant breeding
Origin of salinity in Australia
• Salt in the Australian landscape has mainly come from
the sea via wind and rain
• The concentration at the soil surface depends on the
rainfall and the type of vegetation
• In higher rainfall areas (300-500 mm) rising water tables
brings salt to the surface of cleared land
• In low rainfall areas (250 mm and below), the salt stays
below the soil surface, in the root zone
Areas in which there is land at
risk of rising water tables
(National Audit 2001)
Perth
Sydney
Adelaide
Brisbane
Melbourne
Hobart
Cairns
Where rainfall exceeds crop use,
and unused water escapes below
the roots, rising water tables can
bring the salt to the surface
WA
NSW WA
Secondary salinity – seepage or “rising watertable” salinity
Two types of
dryland salinity
Salt rises to the surface
Salt stays below ground
P. Rengasamy
Aust J Exp Ag 2002;
“seepage salinity” surface sodicity is indicative of
subsoil or “transient salinity”
Primary salinity – subsoil or “transient” salinity
Where crop use
exceeds rainfall,
salts concentrate in
the root zone
Low rainfall areas (<250-300 mm) have natural subsoil
salinity or “transient salinity”, not connected to water
tables
Natural subsoil salinity
(salt is low at the soil surface, and increases with depth)
soil surface 2
4
6
8
10
Metres below
soil surface
0 50 100 150 mM NaCl (1/3 seawater)
Based on YP Dang et al. Aust J Soil Res, (2010) Fig 5.
Rainfall in the south-west of WA
Indian Ocean Climate Initiative Note No 5 (2005)
Indian Ocean Climate Initiative Note No 5 (2005)
Growth response of the world’s two staple crops,
and the most useful two halophytes
NaCl (mM)
0 200 400 600 800
Sh
oo
t D
W (
% c
on
tro
l)
0
20
40
60
80
100
120
tall wheatgrasswheat
saltbushrice
seawater
Old man saltbush
Atriplex nummularia
with inter-rows of tall
wheatgrass
Ed Barrett-Lennard,DAFWA & UWA
Farmers say:
“Every saltbush plant paid for itself in the 2001/02 drought… “
Photo. M. Lloyd
Photo M. Lloyd
“ …and again in floods of Jan 2006”
Ed Barrett-Lennard, DAFWA & UWA
1. Tight control of salt entering plant with water –
over 95% is excluded from leaves
2. Cells in leaves can tolerate extremely high
concentrations – well over seawater concentrations
3. Bladders on leaves excrete excess salt
4. Seeds do not germinate until after heavy rain
5. Some species are annuals, some perennials
6. Fast growth
What makes saltbush so tolerant?
Salt bladders
on surface of
saltbush leaves
(scanning electron micrograph
by Richard Storey)
NaCl (mM)
0 50 100 150 200 250 300
Sh
oo
t g
row
th (
% c
on
tro
l)
0
20
40
60
80
100
tall wheatgrass
barley
wheatdurum wheat
sea barleygrass
Diversity in salt tolerance in the wheat/barley family
at the salinities found in the Australian wheat belt
Colmer, Munns and Flowers, Aust J Exp Agric (2005)
Durum wheat is used for pasta and couscous
0 10 20 30 40
Time after NaCl added (d)
0
1
2
3
4
5
To
tal d
ry w
eig
ht
(g) Control
Salt
Osmotic effect
Salt-
specific
effect
Munns, Schachtman, Condon, AJPP 1995
Osmotic versus salt-specific effect of
soil salinity on growth
bread wheat
durum wheat
Munns et al. Aust J Plant Phys (1996)
Salt exclusion Tissue tolerance
Root cell - salt excluded
Leaf cell -
salt stored safely
in vacuole NaCl NaCl
Two main mechanisms of salt tolerance The two ways of avoiding salt toxicity
1.
2.
3.
1. Na+ uptake from soil
3. Removal of Na+ into sheath
2. Loading Na+ into the xylem
Control points for Na+ transport in plants
Selecting for natural variation in salt tolerance
Na
+ c
oncentr
ation (
mol gD
W-1
)
0
200
400
600
800
1000
1200
1400
Tamaroi Wollaroi JanzHigh Na+
Low Na+
durum
landrace
durumlandrace
(bread)(durum)(durum)
Accumulation of Na+ in leaves
Physiological mechanism of Nax1 and Nax2
Nax2
Nax1
Nax2: Unloads Na+
from the xylem in roots (HKT1;5)
Nax1: Unloads Na+
from the xylem in
roots and leaf base (HKT1;4)
Physiological mechanism of Nax1 and Nax2
Backcrossing into Australian durum
wheat cultivar
Unique durum
derivative Line 149
(a result of a previous
cross between Triticum
monococcum and a
durum rust-sensitive
cultivar for the purpose
of rust breeding)
durum cultivar
Tamaroi
Richard James,
CSIRO Plant Industry
Andrew Smart (PCT, Narrabri) - 2008
350
450
500
300
250
200
150
400
N
1 km
ECa
(mS m-1)
350
450
500
300
250
200
150
400
N
1 km
350
450
500
300
250
200
150
400
350
450
500
300
250
200
150
400
N
1 km
ECa
(mS m-1)
Munns et al, Nature Biotechnology, 2012
Salt-affected field in northern NSW
Using an EM meter to measure soil salt
Ray Hare, durum breeder,
NSW DPI Richard James, CSIRO
0 - 2020 - 40
40 - 6060 - 80
80 - 90
BLOCK 3
BLOCK 2
BLOCK 1
0
50
100
150
200
250
300
Ch
lori
de
co
nc
en
tra
tio
n in
so
il s
olu
tio
n (
mM
)
Soil depth (cm)
Sodium and chloride increase with
depth, to half-strength seawater
Taking leaf samples for Na analysis
Relationship between soil salinity and yield of
durum wheat cultivar Tamaroi with Nax2 gene
ECa (DS/m)
260 280 300 320 340 360 380 400 420 440 460 480
Gra
in y
ield
(t/
ha
)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Block 1
Block 2
Block 3
+ Nax2
- Nax2
Yield data from different sites with
different salinity
Site mean yield (t/ha)
1.0 1.5 2.0 2.5 3.0 3.5
Yie
ld (
% T
am
aro
i)
70
80
90
100
110
120
130
200309336400 236(ECa)
Yuluma
2009
Ashley
2008
Ashley2009
(Block 1) (Block 2) (Block 3)
Nax2 lines
5004
5042
High salinity Moderate to low
salinity
James et al. Funct. Plant Biol (2012)
Field 2, Moree 2009
Field 1 Block 1 Block 2 Block 3
Gra
in y
ield
(%
Tam
aro
i)
0
80
90
100
110
120
Moree 2008
*
Munns et al, Nature Biotechnology (2012)
Benefit of Nax2 on grain yield
in selected trial sites
Crossing Nax genes from durum into
bread wheat
Carol Blake (CSIRO Plant Industry) making
crosses between durum wheat (male) containing
Nax genes and bread wheat (female) parents
SUMMARY Salt underlies all Australian soils Where rainfall is low, crops use all the water so salt concentrations increase in the subsoil. Crops must be salt tolerant Where rainfall is high, water escapes below the roots and rising watertables bring salt to the surface. Plants employed to lower watertables must be very salt tolerant Genetic improvement in salt tolerance will be fastest when laboratory scientists work together with agronomists and breeders
Acknowledgements
CSIRO Plant Industry
Richard James
Carol Blake
Caitlin Byrt
Shaobai Huang
Evans Lagudah
Wolfgang Spielmeyer
Mark Tester, ACPFG
Matthew Gilliham, Uni Adelaide
Collaborating Breeders:
Ray Hare, NSW DPI
Tony Rathjen, Uni Adelaide
Andrew and Jodie Crowe (growers, northern NSW)