The quest for acid-tolerant lucerne Graham Centre Sheep Forum - - PowerPoint PPT Presentation

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The quest for acid-tolerant lucerne Graham Centre Sheep Forum - - PowerPoint PPT Presentation

Jan 18, 2023 129 likes •479 views

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 pH Ca 5.0 (Scott et al .

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The quest for acid-tolerant lucerne

Graham Centre Sheep Forum

Richard Hayes, Research Scientist

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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
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Lucerne biomass (kg/ha) on an acid soil with and without surface applied lime (L)

1000 2000 3000 4000 5000 6000 Spr 04 Aut 05 Win 05 Spr1 05 Spr2 05 Aut 06 Win 06 Spr 06 Sum 07 Aut 07 Lucerne Luc + L

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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

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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

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Challenges in developing AT lucerne

  • Lucerne genetics

– Is an autotetraploid – Is almost an obligate

  • ut-crosser

– Need to maintain genetic diversity to avoid in-breeding suppression

  • Therefore, rate of genetic

improvement is slower

Photo: B. Dear

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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

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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

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Recent Australian research

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

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Recent Australian research

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

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Source; (Scott et al. 2008)

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Population equal to or greater than nominated root length (%)

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Population equal to or greater than nominated root length (%)

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Source; (Scott et al. 2008)

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Recent Australian research

Seedling validation in high Al soil; (Hayes et al. 2011)

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Recent Australian research

Proportion of population with tap root length equal to or greater than nominated length (%)

20 40 60 80 100

Tap root length (mm)

50 100 150 200 20 40 60 80 100 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 (▲).

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Proportion of population with tap root length equal to or greater than nominated length (%)

20 40 60 80 100

Tap root length

50 100 150 200 20 40 60 80 100 a) Experiment 2; pH 4.34 b) Experiment 2; pH 5.26

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Proportion of population with tap root length equal to or greater than nominated length (%)

20 40 60 80 100

Tap root length

50 100 150 200 20 40 60 80 100 a) Experiment 2; pH 4.34 b) Experiment 2; pH 5.26

pH 4.34Ca Al tolerant populations

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Proportion of population with tap root length equal to or greater than nominated length (%)

20 40 60 80 100

Tap root length

50 100 150 200 20 40 60 80 100 a) Experiment 2; pH 4.34 b) Experiment 2; pH 5.26

pH 4.34Ca Al tolerant populations Increased seedling vigour pH 5.26Ca

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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

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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

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Rhizobia research

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Rhizobia research

Photo: R. Ballard

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Rhizobia research

Photo: R. Ballard

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20 40 60 80 100 NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736 Plants with nodules (%)

  • 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

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20 40 60 80 100 NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736 Plants with nodules (%)

  • 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

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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

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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

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

Mn concentration (mg/kg) of lucerne herbage

500 1000 1500 2000 2500

Plot B2 Plot B3 Plot B4 Mean Critical level Plot G1 Plot G2 Plot G3 Plot G4 20.2 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

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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

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Opportunities

  • 1. Select for Mn tolerance in lucerne populations
  • 2. Greater use of gene markers to further enhance

selection techniques

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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