PLANT BREEDING SYSTEMS

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PLANT BREEDING SYSTEMS

• Diversity and Evolution of Reproduction in
  Angiosperms

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Plants vs. Animals
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Plants vs. Animals

• Flowering plants are generally hermaphroditic.

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Plants vs. Animals

• Flowering plants are generally hermaphroditic.
• Use intermediary agents.

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Plants vs. Animals

• Flowering plants are generally hermaphroditic.
• Use intermediary agents.
• Can reproduce asexually sexually.

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Plants vs. Animals

• Flowering plants are generally hermaphroditic.
• Use intermediary agents.
• Can reproduce asexually sexually.
• Less rigidly controlled development
• meristematic tissue everywhere.

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Asexual Reproduction

• Reproduction of genetically identical individuals
  from a single parent plant.
• Via cloning or agamospermy
• No meiosis, no fertilization, and no
  recombination.

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Advantages of Asexual Reproduction

• Parent plants well-adapted to local environment
  will have offspring with a competitive advantage.

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Advantages of Asexual Reproduction

• Parent plants well-adapted to local environment
  will have offspring with a competitive advantage.
• Colonization with limited dispersal.

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Modes of Vegetative Reproduction
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Modes of Vegetative Reproduction

• Rhizomes
• underground shoots
• Tillers
• aboveground shoots
• Bulblets
• little bulbs
• Bulbils
• inflorescence veg buds
• Cuttings

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Agamospermy/Apomixis

• Seeds w/o gametes
• Production of seeds genetically identical to
  parents asexually, w/o fertilization
• 40 families, 130 genera, 400 species
• Obligative or facultative
• May have evolved independently multiple times
  from sexual ancestors.

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Modes of Agamospermy

• Embryo sac develops w/o meiosis w/ unreduced 2n
  egg cell develops into zygote.

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Modes of Agamospermy

• Embryo sac develops w/o meiosis w/ unreduced 2n
  egg cell develops into zygote.
• Embryo sac aborts and a veg cell from surrounding
  sporophytic tissue (ovary wall) develops into
  zygote.
• Rubus, Taraxacum officinale

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Sexual Reproduction

• Production of offspring through meiosis and
  fertilization of egg by sperm (post-pollination).
• Offspring genetically different from parents due
  to recombination.
• Plants can be both asexual and sexual, with a
  variety of forms.

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Hermaphroditic Flowers

• Self-compatible (SC)
• Capable of self-fertilization or
  cross-fertilization
• Self-incompatible (SI)
• Only capable of cross-fertilization
• Inability of hermaphroditic plant to produce
  zygotes w/ self pollen

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Autogamy

• Self-fertilization
• Pollen transfer within or among flowers of same
  individual
• 25 of plant taxa

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Advantages of Autogamy
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Advantages of Autogamy

• Insures seed set in absence of pollinators.

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Advantages of Autogamy

• Insures seed set in absence of pollinators.
• Overcomes sterility.

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Advantages of Autogamy

• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting both
  sets of genes to offspring.
• Well-adapted genotypes preserved.

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Advantages of Autogamy

• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting both
  sets of genes to offspring.
• Well-adapted genotypes preserved.
• Only single colonizing individual needed.

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Disadvantages of Autogamy
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Disadvantages of Autogamy

• Decreases genetic variability.

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Disadvantages of Autogamy

• Decreases genetic variability.
• Inability to adapt to changing conditions.

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Disadvantages of Autogamy

• Decreases genetic variability.
• Inability to adapt to changing conditions.
• Increases inbreeding depression.
• Reduces heterozygosity and increases homozygosity
  of deleterious alleles.
• More uniform populations.

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Cleistogamy (CL)

• Flowers never open and only capable of
  self-fertilization in bud.
• Inconspicuous, bud-like apetalous flowers that
  form directly into seed capsules.
• Has evolved independently multiple times
• throughout the angiosperms, including some basal
  lineages.
• 488 species, across 212 genera and 49 families.
• Violaceae, Fabaceae, Poaceae

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Cleistogamy (CL)

• Mixed mating systems -can produce both CL and CH
  on an individual.
• CL fls are a back-up in case pollinators
  scarce.
• CL occur after normal flowering period.
• CH fls early spring and CL fls rest of season.
• CL fls occur through mutations with loss of SI.

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Self-incompatibility (SI)

• Involves a biochemical rxn in the stigma/style to
  reject self pollen and prevent pollen tube
  growth.
• Genetically controlled by S-locus
• opposite S alleles attract
• like S alleles repel

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Sporophytic SI

• Diploid genotype of sporophyte parent determines
  what matings will be successful.
• Interaction between pollen exine and stigma/style
  tissues.
• Pollen will not germinate on stigma of flower
  that contains either of 2 alleles in sporophyte
  parent that produced pollen.

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Gametophytic SI

• Haploid genotype of pollen grain (gametophyte)
  determines what matings will be successful.
• Interaction between pollen tube and stigma/style
  tissues.
• Pollen grain will grow in any pistil that does
  not contain the same allele.
• 50 of angiosperms

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Advantages of Self-Incompatibility
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Advantages of Self-Incompatibility

• Prevents selfing and expression of deleterious
  genes that are heterozygous in parents.

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Advantages of Self-Incompatibility

• Prevents selfing and expression of deleterious
  genes that are heterozygous in parents.
• Reduces inbreeding depression.

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Advantages of Self-Incompatibility

• Prevents selfing and expression of deleterious
  genes that are heterozygous in parents.
• Reduces inbreeding depression.
• Increases genetic exchange/diversity.

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Advantages of Self-Incompatibility

• Prevents selfing and expression of deleterious
  genes that are heterozygous in parents.
• Reduces inbreeding depression.
• Increases genetic exchange/diversity.
• Ability to adapt to changing conditions.

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Disadvantages of Self-Incompatibility
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Disadvantages of Self-Incompatibility

• Relies on effective cross-pollination, seed
  dispersal and establishment.

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Selfers vs. Outcrossers

• SC
• Small flowers (few)
• Unscented flowers
• Nectaries nectar guides absent
• Maturation of reproductive parts
• Anthers near stigma
• Style included
• All fruits mature
• Low pollen/ovule ratio

• SI or SC
• Large showy flowers (many)
• Scented flowers
• Nectaries nectar guides present
• Differential maturation of reproductive parts
• Anthers far from stigma
• Stigma well-exserted
• Only some fruits mature
• High pollen/ovule ratio

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Strategies to Prevent Self-fertilization
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Physical Separation of Reproductive Parts
(Herkogamy)

• Within flowers

• Among flowers

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Heterostyly

• Flowers in different individuals of the same
  species having 2 or 3 different style lengths
• With stamen lengths varying inversely
• Distyly
• Tristyly

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Distyly

• 2 floral morphs.
• Thrum flower
• long filaments w/ short styles
• Pin flower
• short filaments w/ long styles
• Only pollinations between different floral morphs
  are successful.
• E.g. Primula

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Tristyly

• 3 floral morphs
• Style long, stamens short and medium
• Style medium, stamens short and long
• Style short, stamens medium and long

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Physical Separation of Reproductive Parts

• Unisexual flowers
• Staminate and carpellate flowers
• Monoecy
• Dioecy

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Monoecy

• Common in wind-pollinated plants.
• Common in temperate regions.
• Self-pollination possible but less likely.

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Dioecy

• 4 of angiosperms
• Scattered throughout
• Common in tropical regions and oceanic islands
• Gen small fl size
• 100 outcrossing, but inefficient
• Often controlled by sex chromosomes
• Silene

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Polygamous Flowers

• Both bisexual and unisexual fls on the same
  plant.
• Androdioecy bisexual and staminate individuals
  in a population.
• Andromonoecy bisexual and staminate flowers on
  same individual.
• Euphorbia, Solanum
• Gynodioecy bisexual and carpellate individuals
  in a population.
• Sidalcea hendersonii, Silene
• Gynomonoecy bisexual and carpellate flowers on
  same individual.
• Silene, Solidago
• Polygamodioecy some plants with bisexual and
  staminate flowers some plants with bisexual and
  carpellate flowers in a population.
• Polygamomonoecy bisexual, staminate, and
  carpellate flowers on same individual.

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Evolution of Dioecy

• From hermaphroditism
• Vestigial sex organs
• Few families entirely dioecious
• From monoecy
• From SC
• W/in groups that have lost original GSI system
• From distyly
• Unequal pollen flow gender function
• Change in pollinator frequency
• Non-functional anthers at low level in female
  flowers
• Non-functional pistil in male flowers

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Temporal Separation of Reproductive
Parts(Dichogamy)
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Temporal Separation of Reproductive
Parts(Dichogamy)

• Protandry
• Anthers release pollen before stigma receptive
• Common in insect-pollinated plants
• Geranium maculatum
• 1st day flower
• 2nd day flower

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Temporal Separation of Reproductive
Parts(Dichogamy)

• Protogyny
• Stigma receptive before pollen release
• Less common than protandry
• Magnolia grandiflora
• 1st day flower
• 2nd day flower

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Geitonogamy

• Self pollination between different flowers on
  same plant.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.
• Ancestral angiosperms were SC, hermaphroditic.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.
• Ancestral angiosperms were SC, hermaphroditic.
• SI has evolved many times.
• SC has evolved from SI plants as well.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.
• Ancestral angiosperms were SC, hermaphroditic.
• SI has evolved many times.
• SC has evolved from SI plants as well.
• Physical and temporal separation have evolved
  many times.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.
• Ancestral angiosperms were SC, hermaphroditic.
• SI has evolved many times.
• SC has evolved from SI plants as well.
• Physical and temporal separation have evolved
  many times.
• Dioecy has evolved many times.

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Evolution of Breeding Systems

• Evolutionary trends go both ways and in a variety
  of ways.
• Ancestral angiosperms were SC, hermaphroditic.
• SI has evolved many times.
• SC has evolved from SI plants as well.
• Physical and temporal separation have evolved
  many times.
• Dioecy has evolved many times.
• Breeding systems not fixed, but labile.