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)