The quest for acid-tolerant

lucerne

Graham Centre Sheep Forum

Richard Hayes, Research Scientist

Why do we want Acid-tolerant (AT)

lucerne?

Soils of SNSW are generally acidic

– 74% of ~ 4700 soils in SW NSW had pHCa ≤ 5.0 (Scott et al. 2007)

Lucerne is the only perennial legume broadly adapted across this region

Lucerne is sensitive to acid soils

NSW represents ~ 50% of domestic lucerne sales

Acid soil tolerance has proven to be useful in other forage and crop species

More than a dozen scientific articles exist internationally describing the need for AT lucerne

Still, no AT lucerne cultivar exists today

Lucerne biomass (kg/ha) on an acid soil with

and without surface applied lime (L)

0

1000

2000

3000

4000

5000

6000

Spr 0

4

Aut 0

5

Win

05

Spr1

05

Spr2

05

Aut 0

6

Win

06

Spr 0

6

Sum

07

Aut 0

7

Lucerne

Luc + L

Challenges in developing acid soil

tolerance Soil is highly variable

– Up to 1.5 pH unit difference in 1 m2 soil

A range of acid soil-related factors

– H+ toxicity

– Al toxicity

– Mn toxicity

– Δ nutrient availability (eg Mo deficiency)

Other factors affecting plant response eg topography, soil depth, water holding capacity etc

Challenges in developing AT lucerne

We are starting off a low

base

– Devine et al. (1976)

estimated that Al

tolerance existed in only

2% of a lucerne

population

Lucerne is sensitive to a

range of acid soil factors

– Eg Mn & Al toxicity

Photo: B. Scott

Challenges in developing AT lucerne

Lucerne genetics

– Is an autotetraploid

– Is almost an obligate

out-crosser

– Need to maintain

genetic diversity to avoid

in-breeding suppression

Therefore, rate of genetic

improvement is slower

Photo: B. Dear

Challenges in developing AT lucerne

Lucerne is a legume

Root nodule bacteria (RNB)

is commonly more sensitive

to acidity than the plant

Therefore, for genuine acid

soil tolerance you need:

– AT plant

– AT RNB

– The AT plant to be

compatible with the RNB

Summary – why doesn’t AT lucerne

exist? A range of acid soil factors to consider

Sensitivity to multiple acid soil factors

Starting from a low base

Need to select a large number of elite individuals to develop

a robust population

Need to consider the RNB

Need to ensure the elite RNB is compatible with the elite

plant germplasm

In a context where public plant breeding programs are not

fashionable

Recent Australian research

Screening in high Al solution culture; (Scott et al. 2008)

Recent Australian research

Screening in high Al solution culture; (Scott et al. 2008)

Sensitive Tolerant

Source; (Scott et al. 2008)

Po

pu

latio

n e

qu

al to

or

gre

ate

r th

an

no

min

ate

d

roo

t le

ng

th (

%)

Po

pu

latio

n e

qu

al to

or

gre

ate

r th

an

no

min

ate

d

roo

t le

ng

th (

%)

Source; (Scott et al. 2008)

Recent Australian research

Seedling validation in high Al soil;

(Hayes et al. 2011)

Recent Australian research P

roport

ion o

f pop

ula

tion w

ith t

ap r

oot

length

equal to

or

gre

ate

r th

an

nom

inate

d length

(%

)

0

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60

80

100

Tap root length (mm)0 50 100 150 200

0

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80

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0 50 100 150 200

a) Experiment 2; pH 4.34

d) Experiment 3; pH 5.36

c) Experiment 3; pH 4.48

b) Experiment 2; pH 5.26

Fig. 2. The distribution of length of seedling tap roots exhibiting

evidence of increased Al tolerance (●) and 3 populations exhibiting

evidence of increased seedling vigour (○) compared with individuals

from 6 control populations (▲).

Pro

port

ion o

f pop

ula

tion w

ith t

ap r

oot

length

equal to

or

gre

ate

r th

an

nom

inate

d length

(%

)

0

20

40

60

80

100

Tap root length (mm)0 50 100 150 200

0

20

40

60

80

100

0 50 100 150 200

a) Experiment 2; pH 4.34

d) Experiment 3; pH 5.36

c) Experiment 3; pH 4.48

b) Experiment 2; pH 5.26

Pro

port

ion o

f pop

ula

tion w

ith t

ap r

oot

length

equal to

or

gre

ate

r th

an

nom

inate

d length

(%

)

0

20

40

60

80

100

Tap root length (mm)0 50 100 150 200

0

20

40

60

80

100

0 50 100 150 200

a) Experiment 2; pH 4.34

d) Experiment 3; pH 5.36

c) Experiment 3; pH 4.48

b) Experiment 2; pH 5.26

pH 4.34Ca

Al tolerant populations

Pro

port

ion o

f pop

ula

tion w

ith t

ap r

oot

length

equal to

or

gre

ate

r th

an

nom

inate

d length

(%

)

0

20

40

60

80

100

Tap root length (mm)0 50 100 150 200

0

20

40

60

80

100

0 50 100 150 200

a) Experiment 2; pH 4.34

d) Experiment 3; pH 5.36

c) Experiment 3; pH 4.48

b) Experiment 2; pH 5.26

pH 4.34Ca

Al tolerant populations

Increased seedling vigour

pH 5.26Ca

Population pH 4.34 pH 5.26

Sardi 7 58.7 110.6

CRCSA 34-

36 81.9 107.6

Table 1. Mean seedling root length (mm) for a pair

comparison under low and high lime rates

Population pH 4.34 pH 5.26

Sardi 7 58.7 110.6

CRCSA 34-

36 81.9 107.6

Table 1. Mean seedling root length (mm) for a pair

comparison under low and high lime rates

40% increase

Rhizobia research

Rhizobia research Photo: R. Ballard

Rhizobia research Photo: R. Ballard

0

20

40

60

80

100

NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736

Pla

nts

with n

od

ule

s (

%)

Fig. 3. Effect of inoculation treatment on the percentage of

SARDI ten lucerne seedlings forming nodules in solution culture

(pH 4.8), at 11 days after inoculation.

Courtesy: R. Ballard, SARDI, Adelaide

0

20

40

60

80

100

NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736

Pla

nts

with n

od

ule

s (

%)

Fig. 3. Effect of inoculation treatment on the percentage of

SARDI ten lucerne seedlings forming nodules in solution culture

(pH 4.8), at 11 days after inoculation.

Courtesy: R. Ballard, SARDI, Adelaide

From Book Book, NSW

Progress to date:

Developed a methodology for mass recurrent

selection of seedlings in high Al solution culture

Demonstrated up to 40 % increased tap root

growth at pH 4.3

Have selected a replacement RNB strain for

lucerne adapted for acid soils

Have made further plant selections to develop an

elite lucerne/RNB combo, for commercial release

from 2015

Challenges ahead

Mn toxicity

No selection for Mn toxicity

has yet taken place within

elite Al lucerne

Populations selected for

enhanced growth under

high Al are unlikely to be

tolerant of Mn toxicity

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Mn c

oncentr

atio

n (

mg/k

g)

of

lucern

e h

erb

age

0

500

1000

1500

2000

2500

Plot B2

Plot B3

Plot B4

Mean

Critical level

Plot G1

Plot G2

Plot G3

Plot G4 2

0.2

2.5

7.1

14

.3 5.4

4.4 11

.8

6.3

22

.3

22

.7

26

.1

53

.6

47.7

50.4

44.1

12

.7

38

.7

10

.5

4.9

19

.7

5.7

13

.3

13

.3

23

.2

11

.8 33

.8

37

.3

51.3

29.9

42.9

34.3

(Hayes et al. 2012)

Binalong

Gerogery

Critical threshold

Mn toxicity

Reduced shoot growth by 20%

Reduced lucerne seedling survival by up to 35%

Reduced root length by 40%

Therefore, has the potential to offset all the

existing gains delivered through enhanced Al

tolerance

Opportunities

1. Select for Mn tolerance in lucerne populations

2. Greater use of gene markers to further enhance

selection techniques

Conclusions

Al tolerant lucerne is coming

Likely to be accompanied by RNB with enhanced

performance on acid soils

New products unlikely to be tolerant of Mn toxicity

When those products become available, be sure to

use them in conjunction with lime