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 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 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.

Regions of Domestication

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 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 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 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 openpollinated populations. Genetic variability allows crop production under different environmental conditions.

Germplasm Collection and Gene Banks A plant s germplasmis the sum total of its genes. Current agricultural varieties are often genetically uniform, and thus may not be good sources of genetic variability. Gene Bankshave 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 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 Germplasm Gene Splicing and Transgenic Plants Transgenic Plants are produced by inserting genes from one plant into another. - Recombinant DNA Restriction Enzymescut DNA into fragments with sticky ends.

Plant Breeding Using Sexually Incompatible Germplasm Plasmidsare commonly used as cloning vectors. Small circular bacterial DNA. After cloning, the gene is inserted into plant cells via transformation. Agrobacterium tumefaciens Particle Guns

Bacterial Gene Cloning

Making A Transgenic Plant

Transgenic Plants Pros Transgenic crops are often environmentally friendly. Cons - Farmers can use fewer pesticides. Effect on non-target organisms, such as insects, in the food web. Movement of herbicide resistance to weeds.

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 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 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.

Cuttings and Air Layering

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.

Micropropagation Asexual Plant Propagation 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 Propagation Micropropagation usually begins with the establishment of an explant in tissue culture. Plant parts are disinfested. Induced to develop multiple shoots. Microshootsseparated and placed in a new medium by subculturing. Root Formation Transfer plants back to outdoor environment.

Review Crop Plant Evolution Plant Breeding Sexually Compatible Germplasm Sexually Incompatible Germplasm - Bacterial Gene Cloning Transgenic Plants Seed Propagation Asexual Plant Propagation