Terry Rose, Southern Cross Plant Science/Southern Cross GeoScience

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Enhancing internal phosphorus use efficiency in
crops concepts and approaches
Terry Rose, Southern Cross Plant
Science/Southern Cross GeoScience
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Internal phosphorus use efficiency

• Three main ways we examine it
• Molecular and physiological responses from P
  starved model plants (e.g. arabidopsis)
• Investigate mechanisms in highly P-efficient
  non-crop species
• Investigate and attempt to exploit genetic
  variation within a crop species

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Definitions of Internal Phosphorus Use
Efficiency

• Grain yield per unit of P in above-ground tissue
  (g mg-1)
• - yield formation may be independent of P
  use
• - selects against genotypes with low grain
  yield potential
• Biomass yield per unit of P in above-ground
  tissue (g mg-1)
• - inverse of tissue P concentration
• Critical shoot P concentration for 90 maximum
  yield (mg g-1)
• - expensive when screening large numbers
• Shoot biomass/shoot P concentration (g2 mg-1)

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Problem caused by differential P uptake
29 rice genotypes grown in low P soil for 50 d
with four replicates
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Can screening at equal P uptake help?
  low-P soil low-P soil 500 µg P hydroponic 500 µg P hydroponic P hydroponic P hydroponic
  Total P Total DM Total P Total DM Total P Total DM
ShtPUE -0.81 -0.65 -0.43 0.51 -0.30 -0.02
SeedP 0.10 0.07 0.40 0.59 0.10 0.10
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Screening large numbers in hydroponics

• GWAS study needed P controls for two reasons
• Can remove any genotypes that grew poorly in P
  from any analyses poor growth at low-P not
  related to low P but other artefacts
• Can map GWAS peaks under P conditions to find
  loci related to general vigour and not
  specifically related to P

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Genome-wide association study (GWAS) for PUE
Main QTL on chromosomes 1 (indica) and 11 (aus)
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Does internal PUE ranking change with shoot P
content?
There is no presumption that high internal PUE
lines will grow well in the field because they
may lack P uptake genes The aim is to find
loci/gene(s) that can be pyramided into elite
lines in local breeding programs.
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What are the consequences of higher internal
PUE ?
These authors apply The law of conservation of
matter to nutrient use efficiency.
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What are the consequences of higher internal
PUE ?
Source Rose et al. 2013 Frontiers in Plant
Science
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What are the consequences of higher internal
PUE ?

• Obtained same biomass as the wild-type plants
  with a quarter of the P content in shoots, while
  seed yield was not reduced.
• No seed P concentrations shown

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What are the consequences of lower seed P
concentrations?

• Grain quality milling traits in rice, dough
  quality in wheat?
• Human health
• 1. P deficiency in humans? Unlikely.
• 2. phytate
• - Some reports suggest it may have
  anti-cancer properties, recent review
• by Kumar et al. (2010) suggests that
  there is limited evidence for this
• - Strong evidence for its role in binding
  micronutrients, so reduction in
• phytate may be beneficial
• 3. phospholipids
• - play a role in grain quality and human
  health, but may be quite stable
• (Tong et al. 2014)

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What are the consequences of lower seed P
concentrations?

• Seedling germination and vigour
• Two lines of enquiry have led to the conclusion
  that reducing seed P is detrimental to seed
  germination and vigour.
• Studies with low phytic acid (lpa) mutants
• - Low-phytic-acid mutants often have
  impaired germination and vigour
• BUT this is because whole genes are often
  knocked out
• - The only LPA mutant used in breeding
  programs (Barley lpa1-1 Bregitzer et al.
• 2007 Crop Science) has no impact on
  seedling vigour BUT this mutant has a
• 10-14 reduction in seed total P due to
  mutation of a putative sulfate
• transporter.

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Seed germination and seedling vigour

• 2. Studies with low-P seed from P-starved plants
• Half a dozen studies with cereal crops where
  low-P seed have shown reduced germination and
  seedling vigour compared to high-P seed
• These studies do NOT make fair comparisons
  because the low-P seed came from P-stressed
  parent plants
• Most studies were not conducted with agricultural
  soils with a history of P fertilisation, so soils
  were typically highly P-deficient.

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Seed germination and seedling vigour

• 2. Studies with low-P seed from P-starved plants

• Seeds from P-starved plants performed poorly in
  P-deficient soil but no yield difference in
  agricultural soil supplied with P fertiliser
• Subsequent studies with seed lower in P from
  environmental effects found no difference in
  seedling vigour between high- and low-P seed on
  any soil
• Further studies have been conducted and will be
  the focus of the presentation by
• Elke Vandamme

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High P input farming systems

• If seedling vigour can be maintained with lower
  seed P, then perhaps we could breed for lower
  seed P concentrations regardless of internal PUE
  at the vegetative stage. Go for high P uptake and
  low translocation to grains.
• May be a useful trait in high-input farming
  systems where the removal of P in grains is
  significant and drives the need for continual P
  fertiliser input

World phosphate deposits FAO data Australian
deposits are lt 1 of world P resources. Over
70 of resources are held by China and Morocco.
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High P input farming systems
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High P input farming systems
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High P input farming systems
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High P input farming systems
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High P input farming systems

• In an average season in Australia, approximately
  60, 000 tonnes of P (the equivalent of over half
  a million tonnes of super phosphate) is removed
  off-farm in wheat grain at harvest assuming grain
  contains 3 mg P/g.
• Most is exported overseas while some is consumed
  domestically and contributes to high-P landfill
  and the pollution of water bodies in Australia.
• A reduction in grain P concentrations to 2 mg P/g
  would save about 100 million being removed off
  farm each year at 5 per kg P.

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• Current research project
• Global Rice Science Partnership (SCU, JIRCAS,
  IRRI, AfricaRice) project aims to reduce rice
  grain P by minimum 20
• Approaches for breeding crops with low grain
  phosphorus
• Two approaches investigated in the project
• Exploiting genotypic variation
• Molecular approach
• Mutant approach not investigated but may be an
  option later

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GRiSP project Exploiting genotypic
variation Multi-location trials with 20 rice
genotypes over a number of years to look at G x E
interactions for grain P concentration 1. Need
to identify a genetic component that is
independent of grain yield (yield-dilution
effect) 2. Need to make sure low grain P isnt
associated with low plant P uptake! Elke
Vandamme will be presenting data on this
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GRiSP project Molecular approach Identify P
transporter(s) and use RNAi silencing to reduce
gene expression in specific tissue at a specific
time Understand regulatory pathway of genes
involved in grain P loading and find targets for
genetic manipulation
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• Summary
• We have investigated internal PUE at the
  vegetative stage using a method which screens at
  equal P uptake and have mapped loci for high
  internal PUE
• The consequences of high internal PUE will likely
  be a reduction in grain P concentration
• Reducing grain P concentration may be a good
  option by itself, particularly in high-input
  systems
• Further work is needed to ensure lower grain P
  concentration does not adversely affect grain
  quality or seedling vigour

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• Acknowledgements
• Southern Cross University
• Cecile Julia
• Kwanho Jeong
• Alicia Hidden
• Rachel Wood
• Japan International Research Centre for
  Agricultural Science
• Matthias Wissuwa
• Asako Mori
• Juan Pariasca-Tanaka
• Katsuhiko Kondo

• Africa Rice
• Elke Vandamme
• Kazuki Saito
• IRRI
• Tobias Kretschmar
• Funding Agencies
• Global Rice Science Partnership
• Japan Society for the Promotion of Science

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