Standards Addressed: click here

Seed Production
Seeds are produced by flowers. Flowers contain reproductive structures, both male (the stamens) and female (pistils). Stamens produce pollen which contains the male genetic material; and a pistil contains an ovary with eggs holding the female genetic material. To produce seeds, the pollen must reach the pistil – a process known as pollination. In nature pollen travels to the pistil via wind, water (bouncing to the pistil in rain droplets), and with the help of insects like bees, butterflies, and flies (pollinators). Pollinators collect pollen and nectar from flowers for food; in the process, pollen sticks to their bodies. When they travel to the next flower, the pollen is deposited on pistils. Usually seeds are a product of pollen from one plant and the eggs of another, and so inherit traits from two parents.

Just like a human who inherits genetic material from two parents, a seedling doesn’t usually have exactly the same traits as either of its parents. It will be similar, but it may favor the traits of one parent over another, or exhibit a combination of the two parents’ characteristics.

Plant Breeding
With this knowledge, plant breeders work to produce plants that possess specific traits. For example, if they want to produce a shorter version of a bean plant, they will plant many seeds, identify the shortest plants that grow, and then cross pollinate them – that is, they will make sure the pollen from one short plant reaches the flower of another short plant. They collect and plant the resulting seeds, and hopefully the new plants will also be short like their parents. Breeders repeat this process many times with the collected seeds to increase the frequency and dependability of the trait within the population.

Disease resistance is another common desirable trait. Like people, some plants are naturally more resistant to certain diseases. Plant breeders will grow a plot of tomatoes, for instance, and expose them to early blight fungus. They select and cross pollinate the surviving plants, collect their seeds, sow them, and expose this second generation to the fungus to see if they inherited the disease resistance from their parents. As with the bean example above, breeders continue the process numerous times to develop a population that produces consistently disease-resistant plants.

As you can imagine, this can be a very time consuming practice! Scientists must carefully control pollination and harvest seeds from a number of generations until they produce seed that reliably possesses the desired traits. For plants with an annual life cycle, such as corn, it takes 2½ to 3 months between sowing seed and harvesting seed so it may take fewer than 10 years to see a significant, reliable result. For plants such as fruit trees it can take 5 to 7 years for the first generation to produce seeds and so experiments must span many decades! Plant breeders have to collect detailed data, take good care of plants, and be patient for results.

For more in-depth information, have students read the USDA Sci4Kids article on strawberry breeding. To demonstrate the importance of plant breeding research, introduce them to the “Green Revolution.”