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Plant Breeding

Plant Breeding

Teaching Objectives

Beginning concepts

Advanced concepts

Time Required for Exercise

Stage 1: 4-6 weeks (vernalization period in refrigerator)

Stage 2: 3-4 weeks (flowering stage)

Stage 3: Approximately 20 days (seed pod production in RCBr)

Materials Needed

This exercise requires the following per student/team:

Exploratory Questions

Exploration

Stage 1

 1. Place a turnip or Chinese cabbage core in a plastic bag in the refrigerator for four to six weeks (see figure 1). Before refrigeration the Chinese cabbage, cut off most of the outer leaves, leaving a 10 - 15 cm thick stem or core with smaller leaves attached. The cold treatment, called vernalization, simulates overwintering. The plants will convert from vegetative to flowering stage.  Figure 1Fig.1

Stage 2

2. Make a growing container from the bottom of a 2-liter soda bottle. If the bottle is first filled with hot tap water and the cap replaced, the bottom of the bottle will twist off easily. Fill the container with a potting mix that contains some peat moss.

3. After the vernalization period, remove the turnip or Chinese cabbage from the refrigerator. At this time, leaves may already be forming at the top of the turnip and floral buds may be forming down inside the cabbage core. Sprinkler rooting powder (available from a garden store) on the root-end of the turnip, or on the already cut "stem" surface of the Chinese cabbage. This will stimulate root formation.

 4. Place the turnip or Chinese cabbage on the potting mix in the growth container. Keep the potting mix moist at all times. Place your vegetable in good light, but keep it cool and partly covered to prevent excess wilting. The top porting of a 2-liter soda bottle, cut to be approximately 20 cm high, can be used for the cover (see figure 2).   Figure 2Fig.2

 5. Within two to three weeks the plants should produce flower buds (see figure 3). When the first buds appear, plant several quads of Fast Plants. In two more weeks, both the turnip or Chinese cabbage and the Fast Plants should be in flower. Figure 3 Fig.3

Stage 3

6. Construct bee sticks according to the growing instructions for Fast Plants.

 7. Collect lots of pollen from the turnip or Chinese cabbage and pollinate the Fast Plants (see figure 4). If you need to collect more pollen from the turnip or Chinese cabbage flowers, use a fresh beestick. Figure 4Fig.4

8. After pollinating, pinch the remaining flowers buds off the Fast Plants. Seed pods should mature on the Fast Plants after 20 days.

9. Harvest seed from the Fast Plants and plant some in quads and some in growing containers made from the bottom of 2-liter soda bottles. What will this F1 (first) generation look like? Can you grow these plants and cross them? If so, what will the F2 (second) generation look like? When you get this far, you are becoming a plant breeder!

 

Additional Activities

1. F1 Generation Investigation

Plant the seeds that you harvested from the preceding experiment, in as many quads as you want. For comparison, plant one quad of the original parent Fast Plant seed and one quad of packaged turnip seed. Compare the seedling traits of the parents and their F1 offspring. As an additional comparison, start two turnip plants eight or nine weeks before planting the seed of the F1 generation, using the same procedure as in the preceding experiment. The turnips should come into flower at the same time as the Fast Plants parents. Does the F1 generation flower at the same time as the Fast Plants parents? Compare F1 plants with both kinds of parents for height. Can you produce seed when you interpollinate the F1 plants?

2. F2 Generation Investigation

Plant the F2 seeds in large containers. Grow the plants to full maturity. What do these plants look like? Did they produce anything that looks like a vegetable (above or below the soil)?

Background Information for the Teacher

A trip to the produce section of any supermarket illustrates the great diversity that exists among plants. The mature vegetative stages of the various forms of Brassica rapa appear to have little in common. If you examine turnip, Chinese cabbage, pak choi, rapini, turnip greens (with the roots on) and Fast Plants, you see noticeable differences in shape, size and form. (See illustration at top of page). Yet all belong to the same species as defined as a population of organisms having many characteristics in common which produce fertile offspring through exchange of genetic information. This definition can be tested experimentally by cross-pollinating one of these vegetables with Fast Plants. The most likely candidates are the turnip and Chinese cabbage, commonly found in the produce department of the grocery store. To convert turnip of Chinese cabbage to the flowering stage, a cold treatment of four to six weeks is necessary to simulate overwintering. This is called vernalization.

 

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