Plant Breeding and Plant Biotechnology

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Variants in the Reproductive Process
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Apomixis

• Substitute for sexual reproduction
• Development of an embryo w/o sex
• Identified in over 300 species across 37
  families.
• Not rare but relatively uncommon

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Reproductive Behavior

• Obligate Apomict a plant which reproduces only
  by asexual reproduction.
• Facultative Apomict a plant which has the
  potential to reproduce either sexually or
  asexually. Both process may occur simultaneously
  or one may be predominant.
• Within a genus or species, all reproduction
  strategies may be possible

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Apomixis

• Must bypass two different processes
• Meiosis no reduction of chromosome
• Fertilization development of embryo w/o fusion
  of sperm and egg

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Stimulus for Embryo Development

• Autonomous requires no further stimulation -
  embryo and endosperm may be developed before
  flowers open
• Pseudogamy (False-fertilization) development of
  2n gametophyte requires pollination and/or pollen
  tube growth. Sometimes a sperm nucleus fuses
  with polar nuclei, but never with egg

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Genetics of Apomicts

• Apomixis is genetically controlled in most cases
  studied
• Control is complex (multigenic) and recessive to
  sexual reproduction
• Polyploidy may affect apomictic reproduction
• Hybridization tends to increase apomixis

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Use of Apomixis in Breeding

• Production of exact replicas of diploid
• Fix hybrid vigor
• Fix heterozygous status

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Breeding and Pollination Systems
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Plant Breeding Systems
General Issues to consider

• A flower is an adapted leaf specialized for sex.

• Its function is to bring the gametes together
  thus
• forming zygotes with new genetic combinations

• A species survival is dependent on the
  production of offspring adapted to a particular
  environment. Plants have evolved a variety of
  adaptations that either encourage outbreeding
  (cross-pollination) or inbreeding
  (self-pollination or selfing).

• Each breeding system has genetic ramifications

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Basic Terms

• Outbreeding Sexual reproduction between
  individuals (cross-pollination). (It involves two
  individual plants)

• Inbreeding Sexual reproduction within an
  individual
• (self-pollination). (It involves one individual
  plant)

• Sexual Reproduction Meiosis and fertilization.
• The sexual process is a mechanism to bring
• about gene recombination. Recombination is the
  chief
• source of hereditary variation and provides the
  raw
• materials for species to adapt to changing
• environmental conditions.

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Outbreeder or Inbreeder??
Often one can tell just by looking at a flower
whether it cross-pollinates or self-pollinates
OUTBREEDER INBREEDER
Trait Incompatibility Flower Flower size Flower
color Nectories Scent Nector guides Anther
position Pollen Style position Stigma
self-incompatible self-compatible
many flowers few flowers
large flowers small flowers
bright colors mono-colored
nectaries present nectaries absent
scented flowers unscented flowers
nectar guides present nectar guides absent
anthers far from stigma anthers close to stigma
many pollen grains fewer pollen grains
style exserted from flower style included in
flower
stigmatic area well-defined stigmatic area
poorly-defined
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Outbreeding (Cross-pollination)

• Advantages

Increases genetic variability
Strong evolutionary potential
Adaptation to changing conditions
Successful long-term

• Disadvantages

Can destroy well-adapted genotypes
Relies on effective cross-pollination, seed
dispersal and establishment
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Inbreeding (Self-pollination)

• Advantages

Preserves well-adapted genotypes
Insures seed set in the absence of pollinators
Single colonizing individual possible

• Disadvantages

Decreases (or maintains) genetic variability
Evolutionary dead-end
Cannot adapt to changing environmental conditions
Successful short-term