- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Adanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7250) Unit Title: PLANT REPRODUCTION ____________________________________________________________________________ (CLF)7252 Topic: ASEXUAL Time Taught in Year(s) REPRODUCTION 5 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (D-1-5) - Explain the difference between sexual and vegetative propagation. (D-5) - Describe the advantages and disadvantages of vegetative (asexual) propagation as compared to sexual reproduction. (D-6) - Demonstrate four environmental factors that affect the rooting of a stem cutting. (i.e., soil temperature, humidity, light, and rooting media.) (D-1,5) - Describe the process of regeneration in plants (of shoots, and roots) and explain how this relates to vegetative propagation. (D-7) - Demonstrate two of the following types of grafts: whip (tongue), cleft, notch, bark, and side. (D-8) - Demonstrate one of the following types of budding: "T" (shield), chip, patch, and ring. Special Materials and Equipment: Grafting and budding knives, grafting tools, and supplies (budding bands, wax). References: Hartman, H., Flocker, W., and Kofranek, A. PLANT SCIENCE, GROWTH DEVELOPMENT AND UTILIZATION OF CULTIVATED PLANTS. Evaluation: Quiz by instructor TOPIC PRESENTATION: ASEXUAL AND VEGETATIVE REPRODUCTION A. Asexual versus vegatative reproduction 1. Asexual reproduction is the growth of a whole plant from any part of the plant except a fertilized ovule. 2. Vegetative reproduction is asexual reproduction that starts from a vegetative organ (a root, a leaf, or a stem). 3. A single cell can generate a new plant because each cell contains all the genetic information needed to produce an entire plant. B. Why are asexual methods used? 1. Asexual reproduction leads to plants that are genetically identical to the parent plant. a. 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. b. Plants made by asexual means are said to be clones of the parent. A clone is a group of genetically identical organisms. 2. Cloning is useful when the plant has a valuable combination of traits that would be lost in reproduction by seeds. a. This is true of many crop plants, such as fruit trees, that are hybrids made by crossing two or more varieties. b. In making seeds, the valuable hybrid combination of traits is lost because the seed gets only a fraction of the hybrid parent's genes. 3. Asexual reproduction is essential in crops that produce seedless fruits, such as banana, fig, grape, persimmon, and navel orange. 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 fruit trees. a. The use of cuttings also allows agriculturalists to combine the traits of two plants by grafting. b. In a graft, a cutting 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 diseases, while the scion is selected for quality of the fruits, flowers, or foliage that it produces. C. There are three ways to vegetatively propagate a plant. 1. A portion of a plant containing a bud may be able to produce a shoot and root. 2. A root may be able to produce a shoot. 3. A bud may be grafted onto to another plant that already has roots (budding or grafting). D. Cuttings are the most common method of vegetative propagation. 1. Cuttings are classified as stem cuttings, leaf cuttings, leaf-bud cuttings, and root cuttings. 2. In order to successfully produce new plants, these cuttings must be placed in the correct environment. 3. Several environmental factors affect the rooting of stem cuttings. a. The rooting media temperature should be maintained at 75 degrees Farenheit. 1) It should be about 10 degrees Farenheit warmer than the tops of the cuttings. 2) This is best done by providing bottom heat by use of a thermostatically controlled electric heating cable under the cuttings. b. Maintaining humidity is important. 1) For cuttings that include leaves, it is necessary to reduce transpiration. 2) This will keep cuttings from drying out before they can root. c. Subdued light is generally more favorable for root formation. 1) 200 to 500 footcandles is sufficient. 2) Stem tissue developing in complete darkness is more likely to initiate adventitious roots than tissue exposed to light. d. The rooting medium, especially for difficult-to-root species, can greatly affect the percentage of rooted cuttings. 1) It is best if the medium retains moisture, but provides good drainage and aeration. 2) It must be clean and free of decaying organic matter. 3) Sometimes sand, perlite or other mineral components are used alone. 4) An accepted rooting media is the "U.C. Mix" which is fifty percent sand and fifty percent peat moss. 5) Sometimes mixtures are best. 6) There is no ideal rooting mix for cuttings. a) The medium used depends on plant specie, cutting type, season, and type of propagation system. b) Water management of the medium is of prime importance. e. Treatments with the hormones called auxins may promote rooting. 1) The cuttings are dipped in a solution of auxin in water, or a mixture of dry hormone and powdered clay. Then the cuttings are inserted into rooting medium. E. In hard-to-root species, roots may be induced to form on attached stems. 1. A portion of the stem may be buried until roots form; then the connection with the parent plant can be broken. This is called ground layering. 2. A section of stem may be wounded and covered with moist peat moss and a black plastic covering. The combination of injury, moisture, and darkness may lead to slow root initiation. After roots form, the stem can be detached and planted. This is called air layering. F. One of the most ancient methods of plant propagation is grafting. 1. The techniques of grafting were used as early as 1000 B.C. 2. The goal of grafting is to connect or fit two tissues of living plant tissue together in such a way that they will unite and subsequently behave as one plant. 3. There are several steps necessary to complete a graft. a. A short piece of detached shoot (scion) containing one or more buds is united with the stock (part that is rooted). b. Cuts are made on both stock and scion so as to place the cambium of both stock and scion in contact with each other. c. Wounded areas of stock and scion are covered with material which prevents drying and excludes oxygen. (Grafting waxes and grafting seals are available commercially.) d. Callus tissue grows from the cambium of the scion and stock. It intermingles and interlocks, re-establish 1-3 new cambium, and finally produces new vascular tissue permitting passage of nutrients and water between the stock and scion. e. This whole process takes, about 30 days on a deciduous fruit tree. 4. There are 5 grafting "musts" to obtain a successful graft. a. The stock and scion must be compatible. b. The cambium of stock and scion must be in close contact. c. Proper timing is important. d. All cut portions of stock and scion must be covered to prevent drying out. e. Proper care must be given after the grafting job is done to insure continued success. 5. Each technique of grafting requires different tools and procedures, so each must be demonstrated for complete understanding. a. The most common types of grafts include cleft, bark, notch, and side grafting. b. The method selected for an individual plant is determined by characteristics of the plant, age of the plant, and time of year. G. Budding is the placing of a single detached bud upon the stock. 1. Budding will produce the same results as grafting. 2. Budding is usually done on smaller diameter (younger) stock. 3. Requirements for budding are similar to those of grafting. 4. There are 3 times of the year when successful budding can be done: Spring, June, and Fall. 5. There are several methods of cutting the stock and inserting the buds: a. "T" or shield budding. b. Patch budding. c. Chip budding. d. "H" or "I" budding. 6. All methods of budding except chip depend on the bark "slipping" (bark peels away from the wood). 7. Selection and storage of budwood is extremely important in obtaining successful buds. 8. There are limits to the combinations that can be successfully established by budding or grafting. 9. Consult plant propagation books to make sure that stock and scion (or bud) will make compatible union. __________________________________________________________ ACTIVITIY: 1. Demonstrate various methods of budding and grafting to the class. 2. Students should practice making buds and grafts. NOTE: Many of these techniques can be practiced in the classroom with a minimum of supplies. a. The cutting of all scions can be done with practice scionwood. b. The cutting of all types of buds can also be practiced. c. Whip grafts can be completed in the classroom by using 1/4 inch to 1/2 inch stock and scionwood. 3. Each student should then complete a graft and bud in the field or orchard. __________________________________________________________ 7/20/90 sg #%&C