Plant Breeding Methods (CS, HS 541)

Exercise 10 – Insect Resistance, Polyploids, Interspecific Hybridization

Give complete answers, but be brief and specific. Show your work.

20 points total

1. A simplex autotetraploid (Aaaa) was self-pollinated. What is the phenotypic ratio of its progeny? Assume random
chromosome assortment.




2. With regard to alien addition lines:

a. How are the lines developed by plant breeders?


b. How are the lines used in crop improvement programs?




3. What additional problems do breeders have to consider when selecting for disease and arthropod resistance compared to “normal” traits (e.g. cold tolerance)? Briefly discuss 3 of the problems.




4. Suppose your plant breeding class takes a field trip to the US Vegetable Laboratory in Charleston, SC. While at the Vegetable Lab, you visit with Dr. Mark Farnham who is a Brassica breeder. One of his breeding objectives is to develop broccoli germplasm with insect resistance. One of the damaging insect pests of broccoli is imported cabbage worm. The number of imported cabbage worms has been extremely high this summer in Charleston. In one of Dr. Farnham’s broccoli fields, you observe some plants apparently resistant to the imported cabbage worm.

Please hypothesize on the possible type of resistance in the following scenarios and state why you chose that particular hypothesis.

a. In one corner of the field, broccoli plants are free from feeding damage and no cabbage worms are visible on the foliage; their progeny have lots of feeding damage in a subsequent trial.


b. Several plants have a large amount of feeding damage, and worms are observed feeding in the older leaves. However, the plants have lots of leaves which are formed at a higher rate than the surrounding plants, and they have the same yield as plants with no worms on them.


c. Another group of broccoli plants has little feeding damage on the leaves. There are several dead larvae on the leaves of those plants. In addition, a few live worms are observed on the plants but they are not feeding.


d. One plant appears to have waxier leaves than surrounding plants which have significantly more cabbage worms and eggs on them.


e. A group of plants that was bred for earliness, and grown on plastic mulch has been harvested 2 weeks before the other plants in the field were mature; they had no insect damage on them.