Plant Breeding Overview (HS 521)

Exercise 5 – GxE, Index Selection, Resistance

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

20 points total

1. If you had six genotypes tested in 5 environments such that each genotype was ranked according to its performance in that particular environment, which genotype(s) would you select to release and why?  Rank the order of genotypes based on performance over all environments.

E1   E2   E3   E4   E5
G2   G6   G3   G2   G4
G4   G3   G5   G5   G2
G5   G2   G2   G3   G3
G3   G1   G1   G6   G5
G1   G5   G4   G4   G1
G6   G4   G6   G1   G6



2a. Calculate the following selection indices for the families shown below (only 5 of the 300 families tested are shown; best possible quality rating is 9, best possible disease rating is 0):

Independent Culling Level (≥ check), Simple Weighted (35% yield, 40% quality, 25% disease), Elston’s Weight-Free, Baker’s Standard Deviation, and Average Rank.

Yield  Rating   Corrected values    Index for selection
Plant ($/A) Qual Dis Yield Qual  Dis    ICL  SW   EWF  BSD  AR
1    220    1   0  _____ _____ _____ ____ ____ ____ ____ ____
2     35    9   4  _____ _____ _____ ____ ____ ____ ____ ____
3     85    4   6  _____ _____ _____ ____ ____ ____ ____ ____
4    170    8   2  _____ _____ _____ ____ ____ ____ ____ ____
5    115    7   1  _____ _____ _____ ____ ____ ____ ____ ____
Range 30-300 1-9 9-0
Check  170    7   2
Worst   21    1   7
SP      23   1.8 2.1

2b. Which family is the best and which family is worst, considering all three traits?


2c. Why?


3a. What are four strategies for deploying resistance to diseases?



3b. What are three ways disease resistance can be inherited?



3c. What are three factors to consider when evaluating germplasm accessions for disease resistance?



4. 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.




5. 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.

5a. 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.



5b. 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.



5c. 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.



5d. One plant appears to have waxier leaves than surrounding plants which have significantly more cabbage worms and eggs on them.



5e. 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.