Introduction

Plant propagation is the increase in number of individuals of a species, usually accompanied by their spread over a given area. In crop production, our goal is usually to propagate a species that produces a product that is valuable to us and/or society. Propagation may be accomplished by either sexual or asexual means. Sexual means of propagation involves the union of separate male and female gametes; in terms of crop plants this means reproduction through seed. Asexual reproduction is also known as vegetative reproduction. In vegetative reproduction, desirable crop plants are multiplied by using vegetative organs such as roots or stems. In today's lecture, we will discuss the basic principles of vegetative reproduction, and illustrate the process with specific examples in crop production.

2. Many crop plants are propagated by producing seed, but many species are also propagated vegetatively, that is by using vegetative organs such as leaves and stems.

3. Some crop plants have horizontally growing stems or roots which naturally form daughter plants at some distance from the original parent. Examples of this include strawberry and the spider plant (Chlorophytum). These two plants produce horizontal stems known as stolons, which are commonly known as runners. This process is illustrated in the figure below. The tip of each stolon becomes the upright shoot of a daughter plant and eventually this plant will produce it's own root system. Over time the stolon itself senesces and dies and the daughter plant is then independent of the parent plant.

4. Some woody plants have a readiness to form adventitious roots wherever their stems come in contact with the soil. The blackberry uses this as a natural means of vegetative propagation. It's long stems droop under their own weight and any nodes which come to rest on the soil quickly put down adventitious roots and form daughter shots from axillary buds.

5. Other plants, such as couch grass produce underground horizontal stems known as rhizomes. The apical bud at the tip of the rhizome, or any axillary bud along it's length, is capable of growing into an aerial shoot with it's own adventitious root system. While this may provide some advantage for crop producers, it may be a major disadvantage if the grower is combatting a weed that is propagated by rhizomes. One major weed that is propagated by rhizomes is johnsongrass. One study showed that johnsongrass, under ideal growing conditions, could produce over 180 feet of rhizomes in 1 month.

6. Apical buds on rhizomes, or axillary buds are capable of growing into an aerial shoot with it's own root system.

7. One of the major world crops, the potato, is propagated vegetatively. The potato itself is a tuber. Botanically speaking, the potato tuber is the tip of a swollen stolon. The 'eyes' of the potato are considered to be axillary buds, and the eye at the end is considered to be the apical bud.

8. One potato plant may produce many tubers, each capable of growing into a new plant, as shown in the figure provided. After a period of dormancy, some of the buds or eyes on the tuber begin to sprout and give rise to aerial shoots. Normally apical dominance ensures that the apical bud develops first and most strongly, but if the apex of the tuber is damaged, many of the axillary buds may sprout simultaneously. If a tuber is split up, any portion with at least one bud can give rise to a plant.

9. What advantages does vegetative propagation offer a plant in comparison with reproduction by seed?

10. What disadvantages are associated with vegetative reproduction?

11. Name several crop plants that are propagated vegetatively

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12. Some ornamental crops, such as crocus and gladiolus, form corms, which are swollen stem bases, as shown in the diagram provided. A corm serves as a region of food storage as well as a reproductive structure. It contains undeveloped vegetative and floral buds. Corms produce side-shoots that in turn form small corms known as offsets, which can be separated from the main shoot and planted individually.

13. In some instances of vegetative propagation, artificially induced formation of adventitious roots on portions of stem is the means of propagation. This is known simply as rooting. Some instances of rooting depend on the tendency of certain stems to form roots when they are embedded in soil. One example of natural rooting occurs in blackberries, and this property can be used to propagate blackberries commercially.

14. It is generally the humidity of the soil that induces rooting. A portion of some stems placed in any humid environment will often form adventitious roots. Shoots which are cut from the parent plant for rooting are known as cuttings. Cuttings of some plants, such as the willow, will root very readily when the base is inserted into moist soil.

This web site maintained by Dr. Phil Shuler (shuler_p@fortlewis.edu)