Genotypic Differences in Nutrient Deficiency

Introduction

• Genotypic differences in nutrient deficiency fit under how to remedy deficiencies.

Efficiency Defined

• Efficiency is comparable to a car's kilometers per liter of petrol.
• A plant's efficiency is the ratio between input (resources from soil, air, sunshine) and output (useful products and byproducts).
• $Efficiency = \frac{Useful Output}{Input}$
• Nutrient efficiency is how much useful output is produced per unit of nutrient input.

Nutrient Supply and Yield

• Efficient genotypes show substantial yield increases with small nutrient supply increases.
• Inefficient genotypes require significant nutrient supply before yield increases.
• There is a range of genotypes between efficient and inefficient.
• The relationship between nutrient supply and yield is a saturable response.

Defining Nutrient Efficiency

• Standard cultivar is used as a baseline.
• Some genotypes are better or worse than the standard.
• Efficiency can be defined by growth, yield, or nutrient accumulation in the grain.
• Nutrient Uptake Efficiency:
  • Total accumulation in plants.
  • Per unit root.
• Utilization Efficiency: Biomass produced per unit of nutrient taken up
• Fertilizer Responsiveness: Genotype's response to fertilizer application.

Fertilizer Responsiveness and Genotypes

• X-axis: Increasing yield with low nutrient input.
• Y-axis: Increasing yield with high nutrient input.
• High yield with low nutrient input = high efficiency.
• Bottom parts of the graph are non-responsive to fertilizer.
• Upper parts of the graph are responsive to fertilizer.
• Four Quadrants:
  • Efficient and responsive (best).
  • Inefficient and non-responsive (worst).
• Genotypes tend to scatter across all four quadrants.

Real-World Examples

• Australian wheat genotypes scatter across the quadrants.
• Mendoza is efficient at low nutrient supply.
• SPIA is more fertilizer responsive than Mendoza.
• Focus is on nitrogen, but other nutrients can be tested.

Mechanisms Contributing to Nutrient Deficiencies

• Acquisition Efficiency:
  • Root morphology (inherent and responsive to external stimuli).
  • Mycorrhizae (symbiotic relationship).
  • Root physiology/biochemistry (Michaelis-Menten equation).
    • $K<em>m$ (Michaelis-Menten constant) represents affinity. Low $K</em>m$ = high affinity.
    • $C_{min}$: Uptake can start at a lower concentration of a nutrient.
• Plants alter rhizosphere properties:
  • Cation/anion uptake ratio influences pH.
    • Nitrate uptake increases pH.
    • Ammonium uptake decreases pH.
  • Exudation of chelating/reducing compounds and protons affects nutrient availability.
• Utilization Efficiency:
  • Transport within the root and to shoots.
  • Nutrient retention in roots vs. shoots; shoots need the majority of nutrients.
  • Processes operate at low nutrient requirements.
  • Re-translocation from older to younger leaves and vegetative to generative parts.
  • Large seed reserves.

Nutrient-Specific Interplay: Utilization vs. Uptake Efficiency

• Calcium
  • Utilization efficiency is critical due to poor phloem transport.
  • Transport to young tissues (apical meristems) is crucial.
  • Cells operating at lower nutrient levels increase efficiency.
  • Example: Tobacco genotypes with and without calcium deficiency symptoms.
    • Total calcium concentration is not the differentiating factor.
    • Oxalic acid binds calcium, forming non-soluble oxalates.
    • Soluble calcium concentration is the key.
• Phosphorus
  • Both utilization and uptake efficiency are important.
  • Increase in influx, more root hairs, greater root/shoot ratios.
  • Efficient usage of stored inorganic phosphate ($P_i$).
  • Translocation between different plant parts.
  • Example: Ryegrass vs. clover species.
    • Ryegrass produces more biomass with the same phosphorus supply.
    • Larger root system supports higher phosphorus uptake.
  • Bean genotypes under deficient phosphorus supply.
    • Genotype choice is crucial in farming situations.
    • Dry seasons exacerbate phosphorus deficiency due to reduced diffusion.
• Iron
  • Strategy One: Acidification and exudation of chelating substances.
  • Strategy Two: Phytosiderophore system.
  • Soybean (Strategy One) vs. various grass species (Strategy Two).
  • Differences appear when plants are iron-hungry.
• Copper
  • Wheat cultivars differ in copper efficiency.
  • Rye is resistant to copper deficiency.
  • Triticale (wheat-rye hybrid) can inherit copper efficiency from rye.
  • Transferring a piece of rye chromosome to wheat can improve copper efficiency.
  • Genetic background influences the effectiveness of transferred traits.
• Zinc
  • Phytosiderophores increase zinc uptake.
  • Both uptake and utilization efficiency are important.
  • Genotypes differ in phytosiderophore exudation.
  • Example: Borigal increases zinc uptake in later stages.
  • Shoot zinc concentration varies among genotypes.

Practical Implications

• Low-zinc soil affects different species differently.
• Weeds can thrive in soils where crops struggle.
• Manganese
  • Galleon genotype is poor in manganese efficiency.
  • Rye is unaffected by manganese deficiency.
  • Manganese spray is crucial for deficient genotypes.