chapter 19 Plant Propagation UW-EXTENSION MASTER GARDENER MANUAL: FOUNDATIONS IN HORTICULTURE Introduction Plant breeding any gardeners plant seed The terms “plant breeding” and In a nutshell… in the ground and watch “genetic engineering” are often it grow. Others browse confused. Both are methods of • Propagating plants is a fun way the garden center for developing new plants with desirable to create new plants. Mvarieties of plants with little thought characteristics. Genetic engineering is • You have to think about plants to where they came from. Some divide essentially a type of breeding. in a diferent way if you plan on plants in their gardens to improve Plant breeding has been practiced saving seeds. vigor or to share with a neighbor. In for thousands of years. It involves • We’re talking plant sex: You studying plant propagation you will pollinating the fowers of a chosen need to understand how learn how to afect a plant’s growth by plant with pollen from another plants reproduce to be able to manipulating environmental growing chosen plant, both with desirable efectively propagate them. conditions, resulting in more plants. characteristics. The seeds produced • For issues not covered in this In gardening, plant propagation refers are then planted and the resulting chapter, contact your county to the many ways of starting new plants are evaluated for their quality. Extension ofce: plants. These various processes of Promising plants are “selected” for counties.uwex.edu multiplying or perpetuating a plant their desirable characteristics or to be species may be by natural or artifcial used for further breeding. With plant means. This chapter introduces breeding, the same pollination could concepts and techniques for growing theoretically occur naturally; human new plants from seed and by asexual involvement directs which two plants methods. are combined. Genetic engineering is a relatively new Learning technology that involves manually inserting the DNA from one organism objectives into the cells of another. In some Understand the biology involved in cases, the gene inserted into a plant 1 plant propagation. is not from another plant, but from Know the conditions for starting a diferent organism altogether. seeds. For example, Bacillus thuringiensis 2 is a bacterium whose DNA is often Demonstrate techniques for inserted into plants to provide pest 3asexual propagation. control. Genetic engineering involves a recombination of genes that could not occur in nature without human involvement. Scan or go to http://goo.gl/ygkkAt for more chapter materials. 331 UW-Extension Master Gardener Manual: Foundations in Horticulture Patents, trademarks, and trade Propagation basics names Plants can be propagated in two main ways: Plants developed through traditional breeding sexually and asexually. Sexual propagation or genetic engineering have a unique, desirable is the recombination of plant genetic material characteristic that can be patented by the to form a genetically unique individual. This government. A patent gives the recipient generally involves the foral parts of a plant, the right to exclude others from asexually pollination that results in the formation of seeds, reproducing, selling, or using the plant for a set and starting plants from seed. time, usually 20 years. Patent holders can sell Asexual propagation produces new plants licenses to producers who are authorized to that are genetically identical to the parent plant propagate the plant, and it is illegal for those by taking a vegetative part of the parent plant without a license to reproduce and sell the plant. (stems, roots, leaves, or other non-reproductive Of the hundreds of thousands of plants available, plant parts) and causing it to regenerate into a only a small number of them are patented. For new plant. a plant to be patented, it must be distinctly diferent from existing cultivars. Patents are not Sexual propagation: awarded for plants found in the wild. Trademarks are words, acronyms, phrases, logos, from seeds or symbols that identify the source or origin of Propagation by seed is a common method of a plant or type of plants. A trademark does not producing new plants. Sexual propagation may be give exclusive rights to the plant as a patent does, cheaper and quicker than other methods, and it is but it prevents others from using the trademark. a way to obtain new cultivars and hybrid vigor. Trade names identify a company name, but do Seed propagation results in a lot of genetic not specifcally identify a plant or product. variability, so ofspring may not have the exact characteristics of the parent plant. Seedling variation is quite high in some plants; many ornamental plants do not come “true” from seed. Other plants are more true to type. Many All-America selections vegetables and annual fowers are easily grown from seed. Some perennials can also be grown All-America Selections (AAS) is a non-proft from seed, but may not fower the frst season. organization that tests and introduces signifcantly improved new fowers, Pollination and fertilization bedding plants, and vegetables grown Pollination and fertilization are processes that from seed. AAS tests are conducted at trial result in the formation of new seeds. grounds throughout North America with • Pollination is transfer of pollen to the female ofcial AAS judges supervising the trial and fower parts by wind or pollinators, such as evaluating each entry. AAS Winners have bees or other insects. been tested for home garden performance • Fertilization is the union of the male and and are quite reliable because of these female reproductive material. unbiased, independent tests. AAS Display Gardens in the U.S. and Canada are open • The stamen is the male portion of the fower to the public to provide gardeners with that produces the pollen. opportunities to view the most recent AAS • The dust-like pollen is contained in the Winners. anthers, the sacs at the end of the flament. • The typical female pistil consists of an enlarged ovary (containing the egg) at the base, a columnar style and the stigma, the organ that receives the pollen on the end. 332 PLANT PROPAGATION chapter 19 chapter When pollen grains land or are placed on the The embryo is a new plant resulting from the stigma, they germinate to form a pollen tube that union of pollen and egg during fertilization. grows down the style to the ovary, allowing the Cotyledons, or seed leaves, are attached to the male reproductive material to move to the egg embryo. Monocotyledons (monocots), such (fgure 1). Once the male reproductive material as grasses, have one cotyledon; dicotyledons fertilizes the egg, seeds can be produced. To (dicots), such as beans, have two cotyledons. understand these processes, it is important to A mature seed contains enough stored food (or know the parts and functions of a fower (see energy source) for seed germination and early chapter 1, Botany). seedling growth. The cotyledons of dicots usually FIGURE 1. The parts and functions of a fower contain this food reserve, while some seeds like monocots have a mass of food reserve called an stamen pistil endosperm. Seed coverings are the seed coat and parts of anther stigma the fruit or seed pod. These structures protect the embryo and food reserve inside the seed and flament style sometimes prevent germination until conditions are suitable. ovary Selective pollination petal Four seed types can be produced by selectively pollinating plants with specifc parents: inbred lines, F1 hybrids, F2 hybrids, and seed mixtures. Inbred lines Inbred lines are created when plants from a single sepal parent line are self-pollinated or interpollinated so they become nearly identical after several Anatomy of a seed generations. These fowers or vegetables are A seed is usually made up of three basic parts often easier and faster to breed and produce. (fgure 2): Common self-pollinated, non-hybrid, and • The embryo purebred annuals and vegetables are suitable candidates for saving seed. • A food supply • Some vegetable seeds that can be easily • The outer protective covering saved include lettuce, beans, peas, herbs, and FIGURE 2. Anatomy of a seed heirloom tomatoes. • Annual fower seeds that can often be plumula successfully saved include cleome, salvia, and nicotiana. hypocotyl embryo radical micropyle cotyledon seed coat 333 UW-Extension Master Gardener Manual: Foundations in Horticulture F1 hybrids Seed saving F1 hybrids are created by crossing two inbred Seed left over in a package after planting can be parent plants—often that difer in several saved for next year’s garden, usually with little important traits—resulting in uniform, often very loss in germination, if stored properly (see “seed prolifc plants. Control of the cross-pollination of storage”). these plants is critical for hybrid seed production. You may also choose to save seed from plants These crosses are made to develop qualities like you grow in your garden from one year to the good vigor, heavy yields, uniformity, disease next. Saved seed may not produce plants that are resistance, and other desirable traits. Hybrids the same as the parent plant. Cross-pollination are often more vigorous than either parent, in some crops may result in altered genetic but cannot breed true. Seeds collected from F1 characteristics, so new plants grown from these hybrids will not produce plants identical to those seeds might have any combination of new from which they were collected. characteristics, such as fruit size, blossom color, F2 hybrids shape, or favor. Some vegetables that are self- pollinated and therefore are good seed-saving F2 hybrids are the result of self-pollination or bets include beans, eggplant, peas, and tomato. indiscriminate pollination of F1 hybrids. These plants are more variable than the original hybrid Seed storage but may maintain some of the characteristics of It is important to store seeds properly to maintain their parents.