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Plant Breeding and Propagation. Outline. Crop Plant Evolution Plant Breeding Sexually Compatible Germplasm Sexually Incompatible Germplasm Bacterial Gene Cloning Transgenic Plants Seed Propagation Asexual Plant Propagation. Crop Plant Evolution.

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Presentation Transcript
  • Crop Plant Evolution
  • Plant Breeding
    • Sexually Compatible Germplasm
    • Sexually Incompatible Germplasm
      • Bacterial Gene Cloning
    • Transgenic Plants
    • Seed Propagation
    • Asexual Plant Propagation
crop plant evolution
Crop Plant Evolution
  • Approximately 200,000 species of flowering plants.
    • Six species provide 80% of calories consumed by humans worldwide.
      • Wheat, Rice, Corn, Potato, Sweet Potato, and Cassava.
    • Eight additional plants complete the list of major crops grown for human consumption.
      • Sugar Cane, Sugar Beet, Bean, Soybean, Barley, Sorghum, Coconut, and Banana.
origins of agriculture
Origins of Agriculture
  • First plants were domesticated in the Near East around 10,000 years ago.
    • Root crops and legumes were domesticated 2,000-3,000 years ago.
      • Plants for forage, decoration, and drugs were first domesticated about 2,000 years ago.
plant breeding
Plant Breeding
  • Plant breeding is accelerated evolution guided by humans rather than nature.
    • Breeders replace natural selection with human selection to modify plant genetics.
      • Primary goal of plant-breeding programs is commonly improved yield.
        • Disease resistance, pest resistance, and stress tolerance contribute to yield.
plant breeding7
Plant Breeding
  • Strategies
    • Self-Pollination - Plants are capable of fertilizing themselves.
      • Tend to be highly homologous.
        • Significant inbreeding
          • Wheat, Rice, Peas, Tomatoes
      • Pure-Line Selection - Collecting seeds from several plants, growing seeds from an individual plant in a row, and then selecting the most desirable row.
plant breeding8
Plant Breeding
  • Cross-Pollination - Plants must be fertilized from other individuals.
    • Tend to be highly heterozygous.
      • Corn, Rye, Alfalfa and most Fruit.
    • Mass Selection - Many plants from a population are selected, and seeds from these plants are then used to create the next generation.
      • Seeds from the best are used to create the next generation.
plant breeding using sexually compatible germplasm
Plant Breeding Using Sexually Compatible Germplasm
  • Outcrossing in cross-pollinated crops often results in hybrid vigor (heterosis).
  • Cross-pollinated plants tend to exhibit inbreeding depression.
    • Modern breeders cross pollinate to delete deleterious alleles.
      • Heirloom Varieties are grown as open-pollinated populations.
        • Genetic variability allows crop production under different environmental conditions.
germplasm collection and gene banks
Germplasm Collection and Gene Banks
  • A plant’s germplasm is the sum total of its genes.
    • Current agricultural varieties are often genetically uniform, and thus may not be good sources of genetic variability.
    • Gene Banks have been established to meet current and future demands of plant genetic diversity.
      • Seeds or other propagules are put into long-term storage.
plant breeding using sexually incompatible germplasm
Plant Breeding Using Sexually Incompatible Germplasm
  • Protoplast Fusion
    • Cells of each species are grown in a liquid nutrient solution.
      • Cell walls are chemically stripped to produce protoplasts.
        • Protoplasts of two species are mixed together and stimulated with the aid of an electric current or chemical solution, to fuse with each other.
          • Few successes
plant breeding using sexually incompatible germplasm12
Plant Breeding Using Sexually Incompatible Germplasm
  • Gene Splicing and Transgenic Plants
    • Transgenic Plants are produced by inserting genes from one plant into another.
      • Recombinant DNA
        • Restriction Enzymes cut DNA into fragments with sticky ends.
plant breeding using sexually incompatible germplasm14
Plant Breeding Using Sexually Incompatible Germplasm
  • Plasmids are commonly used as cloning vectors.
    • Small circular bacterial DNA.
  • After cloning, the gene is inserted into plant cells via transformation.
    • Agrobacterium tumefaciens
    • Particle Guns
transgenic plants
Transgenic Plants
  • Pros
    • Transgenic crops are often environmentally friendly.
      • Farmers can use fewer pesticides.
  • Cons
    • Effect on non-target organisms, such as insects, in the food web.
    • Movement of herbicide resistance to weeds.
seed propagation
Seed Propagation
  • Hybrid varieties are often grown from seed produced by crosses between two inbred parents.
    • Inbred line varieties are typically grown from seed and allowed to self-pollinate.
  • Mature seeds are harvested and stored in a controlled environment.
    • Viability is best when seeds are maintained in cool, dry storage.
seed propagation20
Seed Propagation
  • In preparation for planting, seeds may be dusted with a protectant, such as a fungicide.
  • Seeds must be planted in a suitable bed.
    • Moist soil to allow seeds to imbibe water.
      • Dry enough to maintain suitable oxygen levels.
asexual plant propagation
Asexual Plant Propagation
  • Cuttings
    • Produce adventitious roots.
      • Cells near the wound must dedifferentiate and create a new meristematic region.
  • Layering
    • Tip Layering - Bend tips until they touch the ground, and then cover them with soil.
    • Air Layering - Wounding or Girdling to produce roots.
asexual plant propagation24
Asexual Plant Propagation
  • Grafting
    • Segments of different plants are connected and induced to grow together as one plant.
      • Scion - Top section of a graft.
      • Rootstock - Bottom section of a graft.
        • Successful grafting depends on good contact between the vascular cambium of the scion and that of the rootstock.
asexual plant propagation26
Asexual Plant Propagation
  • Micropropagation
    • Grow and maintain plants in a disease-free status in test tubes.
      • Grown in-vitro in sterile medium.
      • Relies on totipotency of plant cells.
        • Capacity of a cell to give rise to any structure of a mature organism.
asexual plant propagation27
Asexual Plant Propagation
  • Micropropagation usually begins with the establishment of an explant in tissue culture.
    • Plant parts are disinfested.
    • Induced to develop multiple shoots.
    • Microshoots separated and placed in a new medium by subculturing.
    • Root Formation
    • Transfer plants back to outdoor environment.
  • Crop Plant Evolution
  • Plant Breeding
    • Sexually Compatible Germplasm
    • Sexually Incompatible Germplasm
      • Bacterial Gene Cloning
    • Transgenic Plants
    • Seed Propagation
    • Asexual Plant Propagation