Developing New Varieties

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Developing New Varieties

• Larry Darrah
• Research Geneticist and Adjunct Professor
• USDA-ARS Plant Genetics Research Unit
• and Department of Agronomy, UMC

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Self- vs. cross-pollinated crops

• Self-pollinated Uses pollen and egg from the
  same plant to produce seed. ExamplesWheat and
  soybeans.
• Cross-pollinated Uses pollen from one plant to
  fertilize an egg from another plant.
  ExamplesCorn and squash.

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Self- vs. cross-pollinated crops

• SoybeanSelfs easily and crosses with great
  difficulty 3-4 seeds per pollination, if you are
  good! Only about 10 of the crosses set any
  seed.
• WheatSelfs easily and crosses with difficulty
  10-15 seeds per pollination. 95 of the crosses
  will set seed.
• Corncrosses and selfs easily 300-400 kernels
  per pollination. Anyone can pollinate corn!
• Determines what type of product is available to
  the farmer (hybrid vs. variety).

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Corn anatomy

• Tassel - ?
• Sheds pollen at maturity

• Ear - ?
• Each silk is attached to one ovule.
• Pollen tube grows down silk and fertilizes ovule.

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Shoot bagging
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Cutting back the ear
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Tassel bagging
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Pollination
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Terminology

• Inbred A plant that is produced through
  self-pollination over many generations.
• Hybrid A plant that is produced by
  cross-pollinating two inbreds.

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Does plant breeding work?
You betcha it does! Lets look at corn yields
over time.
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Corn yields 1870-2000(10 tons/ha 159 bu/a)
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Howed they do that?
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Population improvement/basis of gain from
selection
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Stalk lodging damage
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Rind penetrometer use
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Rind penetrometer in action
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Divergent selection results
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Response to selectionin MoSCSSS
Cycle 0 and B73 x Mo17
Cycle 6 low and high
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Rind penetrometer resistance
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Recurrent selection

• Generate families.
• Test family performance.
• Recombine selected families to complete a cycle
  of selection.
• Extract inbred lines by selfing in selected
  families and testcrossing at S2 or S3.

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Family structure

• Selfed plants (S1 or S2).
• Crossed plants (Half-sib families with various
  testers.
• Selfed and crossed plants (S1 or S2 testcrosses
  to various testers.
• Reciprocally crossed plants (two half-sib
  testcrossing schemes.

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Family evaluation (Yield)

• Test 100-300 families.
• 2-row plots spaced 30 apart and about 7 between
  plants for a total of 60 plants 26,000-30,000
  plants/a.
• 4-9 replications at 2-6 locations in one season
  (3 reps. at 3 locns., 2 reps. at 4 locns., or
  even 1 rep. at 6 locations might be used.
• Locations are representative of the region of
  adaptation.
• Combine harvest to obtain grain weight, test
  weight, and moisture.

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Recombination of selected families

• Bulked pollen, 1 male for 2 females.
• Diallel 1 x 2, 1 x 3, . . . , 9 x 10 in paired
  rows or by chain crossing where most rows are
  used as both a male and female where the species
  allows (as in corn).

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Partial Diallel
?
?
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Germplasm sources for population improvement

• Existing varieties (landraces and improved
  populations).
• Crosses within heterotic groups of existing elite
  lines for corn.
• Synthetic populations (contain varieties, lines,
  other synthetics, etc.). For example, germplasm
  with resistance to the European corn borer.

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Look at manysave a few!
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Wheat variety Ernie

• Came from pedigree selection in a cross of Pike
  and Exp. Mo9965.
• Pike is an old variety with a very mixed pedigree.

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Triticale A new crop

• Triticale is a cross of wheat (female) and rye
  (male).
• Confers traits of high yield and baking quality.
• Confers traits of tolerance to acid soils and
  salinity, drought tolerance, winter hardiness,
  rust and mildew resistance, and higher lysine.
• Grown on 7.5 million acres (acid and marginal
  soils) in the worldprimarily Australia, Brazil,
  France, Germany Poland, and South Africa.

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New birdsfoot trefoil with rhizomes

• U.S. trefoil has persistence problems because of
  root and crown rot.
• U.S. varieties lack rhizomes.
• Paul Beuselinck, USDA-ARS, Columbia, collected a
  rhizomatous birdsfoot trefoil in Morocco and has
  bred it into U.S. germplasm resulting in release
  of ARS-2620.
• Grazing studies show increased persistence in
  pastures.

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No rhizomes Rhizomes
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Pedigree selection in self-pollinated crops
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Where do most new varieties come from?

• Selfing out of existing varieties and testing.
• Crosses among existing lines and varieties
  followed by selfing and testing.
• Yes, this approach seems to be self-limiting
  (funnel), but it has worked well thus far in many
  crops. See the following data from the Kenya
  Maize Breeding Project

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Genetic variance estimated from ear-to-row
selection in Kitale Composite A (E7) from 1965 to
1974

• Cycle 0 355
• Cycle 1 287
• Cycle 2 242
• Cycle 3 470
• Cycle 4 316
• Cycle 5 283
• Cycle 6 586
• Cycle 7 213
• Cycle 8 1148
• Cycle 9 263

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