- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6250) Unit Title: SEXUAL & ASEXUAL PROPAGATION ____________________________________________________________________________ (CLF6251) Topic: SEXUAL & ASEXUAL Time Year(s) PROPAGATION 2 / 3 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (D-1) - Explain the difference between sexual and asexual (vegetative) propagation, give two examples of each, and demonstrate how they are currently used in horticulture. Special Materials and Equipment: Seeds, growing flat, soil mix, material for cuttings, perlite, and other propagation materials you might want to show. References: Bailey, L. H. (1974). THE NURSERY MANUAL. New York: Macmillan. Hartmann, H. T., & Kester, D. (1983). PLANT PROPAGATION: PRINCIPLES AND PRACTICES (4th ed.). Englewood Cliffs, NJ: Prentice-Hall. Resources: Vocational Education Productions (VEP) (slides, videos, etc.) California Polytechnic State University, San Luis Obispo, CA. Evaluation: By quiz, test, and/or observation TOPIC PRESENTATION: SEXUAL AND ASEXUAL PROPAGATION A. Plant propagation is the multiplication of plants by both sexual and asexual means. 1. The goal of propagation is to increase the number of plants with valuable combinations of traits. 2. Sexual propagation is by seed. 3. Asexual propagation is the increase of plants by vegetative methods (cuttings, budding and grafting, layering, separation, division and tissue culture). B. Sexual Propagation (seed propagation) 1. Most plants are started from seed. 2. Seed propagation is normal for vegetables, flowers, grains, and forest trees. Generally, sexual propagation is the method of choice because of its several advantages: a. Propagation by seed is more economical. b. Propagation by seeds is easier. c. Most seeds can be easily stored for long periods of time. d. Seeds are less likely to transmit diseases to their offspring than are plants started by vegetative means. 3. There are disadvantages of using seeds. a. In most species, plants from seeds are variable or inconsistent (don't breed "true") in genetic makeup (e.g., rose). b. Some plants are slow to mature when grown from seed. c. Some plants do not produce viable seeds (e.g., hydrangea, chrysanthemum). 4. Seedlings of different species are used as rootstocks for many tree species. a. They are used because they have one or more of the following characteristics: 1) dwarfing 2) tolerance to soil problems (drainage, salinity, alkalinity) 3) resistance to disease 4) compatible with the selected variety 5. Seedlings are also used in plant breeding to produce plants with new combinations of traits. a. As parents, the breeder selects two plants that have different desirable traits; for instance, one parent might be disease resistant while the other produces especially beautiful flowers. b. A cross between the parents leads to plants with various combinations of traits. The breeder selects those individuals that have all the desired traits (for instance, both disease resistance and attractive flowers). 6. Examples of seed propagation: a. Marigolds, petunias, vinca, and other annual plants are grown from seed. b. Lawn grasses are started from seed. c. Palms and other monocots are started from seeds. C. Asexual propagation 1. Asexual propagation is the growth of a whole plant from any part of the plant except a fertilized ovule. 2. Vegetative reproduction is asexual propagation that starts from a vegetative organ (a root, a leaf, or a stem). 3. Why are asexual methods used? a. Asexual propagation leads to plants that are genetically identical to the parent plant. 1) This occurs because the cells that start the plant are made from parental cells by mitotic divisions, in which the new cells are identical copies of the parent cell. 2) Plants made by asexual means are said to be clones of the parent. A clone is a group of genetically identical organisms. b. Cloning is useful when the plant has a valuable combination of traits that would be lost in reproduction by seeds. 1) This is true of most ornamentals that are hybrids made by crossing two or more varieties. 2) In making seeds, the valuable hybrid combination of traits is lost because the seed gets only a fraction of the hybrid parent's genes. 4. Some plants are propagated asexually because their seeds are hard to germinate, or because bearing plants can be grown more rapidly from stem or root cuttings. This is true of many woody ornamental plants. a. The use of cuttings also allows hortculturalists to combine the traits of two plants by grafting. b. In a graft, a stem from one plant (the scion) is attached to another plant that serves as rootstock. c. The rootstock may be selected for resistance to soil-borne problems, while the scion is selected for quality of the flowers or foliage that it produces. 5. Asexual propagation is essential in plants that produce few or no viable seeds. 6. There are three ways to vegetatively propagate a plant: a. A portion of a plant containing a bud may be able to produce a shoot and root. b. A root may be able to produce a shoot. c. A bud may be grafted onto another plant that already has roots (budding or grafting). 7. Examples of asexual propagation: a. Rose rootstock is grown from cuttings and then is budded. b. Most house plants are produced by cuttings. c. Orchids are grown by division or tissue culture. d. A large proportion of ornamental trees and shrubs are grown from cuttings. __________________________________________________________ ACTIVITY: 1. The instructor does a demonstration of several different types of propagation, i.e., seed, cuttings, division, etc. 2. Visit a local nursery that does plant propagation as part of its operation. 3. Show films or videos of plant propagation methods. 4. Have the students grow plants from seeds and cuttings. __________________________________________________________ 12/13/90 MT/sg #%&C