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PLANT PROPAGATION

PLANT PROPAGATION. Choice of Methods. Sexual Propagation by seed Asexual (vegetative) Cuttings Grafting Layering Division. Propagation Method Distinctions. Sexual “True” to seed implies . . . No characteristics changed Cultivar termed a Line Line is homozygous

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PLANT PROPAGATION

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  1. PLANT PROPAGATION

  2. Choice of Methods • Sexual • Propagation by seed • Asexual (vegetative) • Cuttings • Grafting • Layering • Division

  3. Propagation Method Distinctions • Sexual • “True” to seed implies . . . • No characteristics changed • Cultivar termed a Line • Line is homozygous • Self-pollinated gives progeny like parent • Cereals and vegetables are examples

  4. Other Seed-propagated Cultivars • Inbred lines • Pure lines, self-pollinated and selected • Used to produce hybrid cultivars • Hybrids • Example: hybrid corn

  5. Propagation Method Distinctions • Asexual (vegetative) • Necessary when plant is heterozygous • Heterozygous implies: • Many dissimilar genes • Meiosis segregates/recombines genes • Seed propagation can’t maintain characteristics of parent

  6. Propagation Method Distinctions • Asexual (cont) • Used with heterozygous plants • Piece of vegetative tissue • Suitable environment • “missing parts” develop • Whole plant genetically identical to original • Flower not involved in asexual propagation

  7. Asexual Propagation Facts • No genetic change (barring mutations) • Heterozygous cultivars carried generations • Cultivars are clones • Numerous methods (see text, Table 5-1)

  8. SEXUAL PROPAGATION • Seed produced in flower • Meiosis involved • Reduction division yields haploid gametes • Gametes combine in fertilization • Zygote develops into embryo

  9. SEED PRODUCTION • Cultivar preservation • Control of seed source essential • If homozygous, self-pollinated . . . • purity assured • If homozygous but cross pollinating . . . • Must separate plants • Prevent pollen contamination

  10. SEED CERTIFICATION PROGRAM • Government standards • Isolation • Culling • Inspection • Final seed testing • Harvesting equipment cleaning

  11. CERTIFICATION PROGRAMS (cont) • Four classes of seeds (agronomic crops): • Breeder seed • White tag; plant breeders • Foundation seed • White tag; public/private foundation stock • Registered seed • Purple tag; progeny of breeder/foundation • Certified seed • Blue tag; sold to farmers; known genetics and purity

  12. Vegetable and Flower seeds • Regulated by seed companies • Seed purity continually tested • Special test gardens

  13. SEED FORMATION • Seed essential parts: • Embryo • Develops into new plant • Food storage material • Nourishes embryo; endosperm/cotyledon(s) • Seed coverings • Seed coats/other parts ovary wall

  14. SEED FORMATION (cont) • Development • Ovary to Fruit • Ovule to Seed • Integuments to Seed coats • Nucellus to Perisperm • 2 polar nuclei/1 sperm to Endosperm (3n) • Egg nucleus/1 sperm to Zygote to Embryo (2n)

  15. SEED STORAGE AND VIABILITY • Some seeds short-lived • Willow, maple, elm • Others may live many years • Hard-seeded legumes • Many seeds range between extremes • Often dependent on storage conditions

  16. SEED VIABILITY TESTS • Cut test • Float • X-ray • Only tell you there is an embryo! • Still don’t tell you the viability!

  17. GERMINATION TEST • % seedlings developing from seeds planted • Use on seeds with no dormancy problems • e.g. flower, vegetable, grain • Several methods • Moist paper towel (simple) • Plant in seed flats (greenhouse) • Germination chambers (seed-testing labs)

  18. CHEMICAL TEST • Tetrazolium Test • Living tissue test • Chemical reacts with enzymes in tissue • Color change • Interpretation variable

  19. EXCISED EMBRYO TEST • Used on wood plant species with dormancy • Don’t respond in direct germination tests • Embryo cut from seed • Seed laboratory technique • Moist paper tested in covered dish • Viable embryos show activity (greening) • Non-viable embryos remain white and die

  20. SEED DORMANCY • Dormancy may allow a seed to resist germination even though conditions would be favorable to germinate • Survival mechanism • May require specific techniques to overcome

  21. TYPES OF SEED DORMANCY • Seed coat dormancy • Impermeable to water and gases (oxygen) • Associated with hard seed coats • Legumes, pine, birch, ash • Natural weathering softens seed coat • Artificial methods: • Scarification • Heat treatment • Acid scarification

  22. TYPES OF SEED DORMANCY • Embryo dormancy • Common in woody perennials • Physiological conditions • Germination blocks in embryo • Break by stratification: • Chilling temperatures • Moisture • Oxygen • Time

  23. ADDITIONAL DORMANCIES • Double dormancy; e.g. Redbud • Rudimentary embryos; e.g. Magnolia • Chemical inhibitors: • Coumarin • Caffeic acid • e.g. tomatoes, lemons, strawberries • Secondary dormancy; e.g. some woodies

  24. GERMINATION REQUIREMENTS • Adequate moisture (varies with species) • Proper temperature (varies with species) • Good aeration • Light (some cases) • Free from pathogens • Free from toxic salts

  25. VEGETATIVE PROPAGATION • Asexual – Not involving flowers or fusion of egg and sperm • Accomplished through mitosis: • Nucleus contains genetics for entire plant • Cells genetically identical • Cells can still differentiate • Capable of becoming any kind of cell • Due to:

  26. VEGETATIVE PROPAGATION • Totipotency – ability of mature cell to return to embryonic state and produce whole new individual • Plant cells easy • Many plants use totipotency to self-propagate • Importance – yields genetically identical plant • Not possible with seed (sexual) reproduction • Meiosis combines genes at random

  27. VEGETATIVE PROPAGATION • Mitosis produces: • Adventitious roots • Adventitious shoots • Callus

  28. VEGETATIVE PROPAGATION • Used primarily for woody perennials • Highly heterozygous • Don’t breed true from seed • Desirable characteristics lost • Produces clones • Fruit, nut, ornamental cultivars • Many are ancient e.g. ‘Thompson Seedless’ grape

  29. Cultivated Clones • Two processes: • Vegetative propagation of superior seedlings • Typical method • e.g. ‘Golden Delicious’ apple • Mutations • Budsports; e.g. ‘Ruby’ from ‘Thompson Pink’ • Chimeras; e.g. variegated pink lemon (fig. 5-6) • Range from slight to serious • Depends on where in mitosis and where in plant

  30. Apomixis • Interesting phenomenon • Asexual production of seedling from seed formation in the usual sexual structures of the flower but without the mingling and segregation of chromosomes • no union of male and female gametes • Seedling characteristics same as maternal parent

  31. Propagation by Cuttings • Classified according to part of plant obtained • Stem cuttings • Hardwood • Semi-hardwood • Softwood • herbaceous • Leaf cuttings • Leaf-bud cuttings • Root cuttings

  32. Grafting • Joining of two separate plant structures • Used on difficult to root plants • Make use of particular rootstock characteristics

  33. Budding

  34. Grafting and Budding Notes • Cambial layers of stock and scion must meet • Parts must be held securely • Keep air out! • Union heals by callus production from parenchyma cells • Adequate temperature for cell division • There are limitations!

  35. Layering

  36. Additional Layering Techniques • Simple layering (like tip layering) • Mound layering • Air layering

  37. Other Plant Structures • Runners (stolons); e.g. strawberries • Suckers (adventitious shoots); e.g. blackberry • Crowns (used in division) • Specialized stems and roots • Bulbs - Tuberous roots • Corms - Rhizomes • Tubers

  38. Tissue Culture • Micropropagation • Utilizes small ‘explants’ • Callus formation • Cell differentiation • First used on ferns, orchids and carnations

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