The quest for acid-tolerant lucerne

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. 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

Aut 07 Sum 07 Spr 06 Win 06 Aut 06 Spr2 05 Spr1 05 Win 05 Aut 05 Spr 04 Lucerne biomass (kg/ha) on an acid soil with and without surface applied lime (L) 6000 5000 Lucerne Luc + L 4000 3000 2000 1000 0

Challenges in developing acid soil tolerance Soil is highly variable Up to 1.5 ph unit difference in 1 m 2 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)

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

Source; (Scott et al. 2008)

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

Recent Australian research Proportion of population with tap root length equal to or greater than nominated length (%) 100 80 60 40 20 0 100 80 60 40 20 0 a) Experiment 2; ph 4.34 b) Experiment 2; ph 5.26 c) Experiment 3; ph 4.48 d) Experiment 3; ph 5.36 0 50 100 150 200 0 50 100 150 200 Tap root length (mm) 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 ( ).

0 50 100 150 200 0 50 100 150 2 Proportion of population with tap root length equal to or greater than nominated length (%) 100 80 60 40 20 0 100 80 60 40 20 0 a) Experiment 2; ph 4.34 b) Experiment 2; ph 5.26 c) Experiment 3; ph d) Experiment 3; ph 5

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 Population ph 4.34 ph 5.26 Sardi 7 58.7 110.6 CRCSA 34-36 81.9 107.6 40% increase

Rhizobia research

Rhizobia research Photo: R. Ballard

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. 100 80 60 40 20 0 NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736 Courtesy: R. Ballard, SARDI, Adelaide

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. 100 From Book Book, NSW 80 60 40 20 0 NO RHIZOBIA RRI 128 SRDI 672 SRDI 722 SRDI736 Courtesy: R. Ballard, SARDI, Adelaide

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

Mn concentration (mg/kg) of lucerne herbage 2500 2000 1500 1000 500 0 44.1 50.4 47.7 34.3 42.9 29.9 51.3 20.2 12.7 2.5 38.7 7.1 10.5 14.3 4.9 5.4 19.7 4.4 5.7 11.8 13.3 6.3 13.3 Binalong Gerogery 22.3 23.2 22.7 11.8 Plot B2 Plot B3 Plot B4 Mean Critical level Plot G1 Plot G2 Plot G3 Plot G4 Critical threshold 26.1 33.8 53.6 37.3 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan (Hayes et al. 2012)

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