PLB143 - Lecture 17

How did plants evolve under domestication? Yield and physiological changes

© Gepts 2008
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Readings

  • Required
    • Evans LT, Fischer RA (1999) Yield potential: Its definition, measurement, and significance. Crop Sci 39: 1544-1551 Pdf version (need Kerberos password)
  • Other
    • Benz B (2001) Archaeological evidence of teosinte domestication from Guilá Naquitz. Proc Nat Acad Sci USA 98:2104-2106
    • Evans LT (1993) Crop evolution, adaptation, and yield. Cambridge Univ. Press, Cambridge, UK
    • Gepts P (2002) Crop domestication as a long-term selection experiment. Plant Breed Rev 24 (Part 2): 1-44. Pdf version
    • Troyer A (2000) Temperate corn - background, behavior, and breeding. In: Hallauer A (ed) Specialty corns, 2nd edn. CRC, Boca Raton
  • Presentation slides:

The concept of yield potential

  • The most important trait:
    • Subsistence agriculture: food or other products
    • Market-linked agriculture: income
  • Distinguish: Bingham (1967), Evans (1993):
    • Potential yield
    • Realized yield
  • Yield potential: “yield of a cultivar when grown in environments in which it is adapted; with nutrients and water non-limiting; and with pests, diseases, weeds, lodging, and other stresses effectively controlled.”
  • Two types of genes:
    • Yield genes (increase yield)
    • Stress-resistance genes (prevent yield reductions)

Comments on the concept of yield

  • Need to specify: Dry matter content: e.g.,
    • Wheat: CA: 2.6-2.8 ton /acre (1 ton = 2000 lbs); = 5200 – 5600 lbs /acre; moisture ~ 10% --> 4680 lbs DM /acre
    • Potato: CA: 370 cwt. /acre (1 cwt = 100 lbs); = 37000 lbs /acre; moisture ~ 80% --> 7400 lbs DM /acre
  • Duration of growing season:
    • Yield/day and total no. of days
  • Where was yield measured?
    • Experiment station, on-farm trials, area averages, etc.
    • Plot size

Early steps in domestication

Example of maize:

Early domesticated types show the following traits

  • Stiff rachis
  • Shallow cupules, perpendicular orientation of lower glumes
  • Two or four rows of seeds:
    a, b: Single spikelet/node c: Two spikelets/node

Possibly, early increases in yield due to simple but radical changes in ear structure

from Benz 2001

Evolution of yield after domestication

  • Evolution of wheat yields in Mesopotamia (Araus et al. 2001) :
    • c. 8000 BC: estimated grown yield was 1560 kg/ha
    • contemporary yields: roughly 1000 kg/ha
  • Maize yields in U.S.A.
    • Flat until 20th century?

from Troyer 2006

How to measure evolution of yield?

  • What kind of experiment?
    • How to go from A1 to B4?
  • Difficulty:
    • Yield increases due to:
      • Agronomy
      • Breeding = genetic improvement
      • Interaction agronomy x genetic improvement
    • Changes in stress environment:
      • Biotic
      • Abiotic
    • Long-term environmental change:
      • CO2 levels
      • Soil fertility
      • Increasing temperature

from Evans and Fischer 1999

Changes in specific traits

Stem height: Introduction of dwarfing genes

  

Pieter Breughel, 1565

Visit to field trial (www.jic.ac.uk/.../ MSc/images/MScCPB.jpg)

Check the difference in plant height between left and right; the introduction of dwarf cereals dates to the mid-20th century.

Interaction between breeding and agronomic practices: e.g., N fertilizer: dwarf cultivars produce higher yields only with increased N fertilizer

Breeding x agronomy interactions

Top: wheat; bottom: maize (from Evans & Fischer 1999)

Evaluations of yield evolution

  • Indirectly:
    • Standard yield trials:
      • Comparison of varieties in field
      • Changes over the years
  • Directly:
    • Historic series of cultivars
    • Linear regression over year

Examples of experiments to measure yield

Indirect

(from http://cvp.cce.cornell.edu/ )

(from http://www.usu.edu/barley/web/logantrial.html )

Direct

(from Ortiz-Monasterio et al. 1997)

Results

  • Simple rates:
    • 0.5- 2.0 %
    • 50/50: breeding vs. agronomic improvement
  • No ceiling
  • Faster for cereals and cotton; slower for legumes and root and tuber crops
  • More rapid in favorable environments

from Evans and Fischer 1999

from Gepts 1998

Importance of genetic diversity

  • The more recent varieties have more parents and also a higher yield

  • Need to know where to find
    genetic diversity! --> Centers of diversity (domestication) (see Lectures 2 (Vavilov) and 10

from Evans and Fischer 1999

Physiological basis of yield increases?

  • Generally, increase in harvest index:
    • From 20-30% wild to 50-70% highly domesticated:
    • Photosynthates from stem to grain
  • Wheat: Development of more distant florets  more grain per ear
  • Maize: Resistance to high density
  • Maize, soybean: Increase duration of photosynthetic activity
  • In general, increase in photosynthetic activity: NOT a factor
  • Other photosynthetic traits well:
    • Increase stomatal conductance
    • Leaf cooling

Donald’s wheat ideotype (noncompetitive, high yield)

  • Ideotype: idealized plant type to achieve high yield in a specific environment and cropping system
  • Traits:
    • short stem (no lodging... but less competitive)
    • fewer leaves (just enough to intercept avail. light)
    • single, nonbranching stem (don’t waste resources contesting space w/ neighbors)
    • early flowering (longer grain fill period)
    • high harvest index (more grain, less leaf+stem)
    • erect leaves (high RUE -- spreads available light over more leaf area)

(from F. Denison)

Conclusions

  • Strong increase in yield with not end in sight
  • Diverse routes to higher yields
    • By design
    • Empirical testing