Plant Breeding Overview (HS 521)

Exercise 2 – Heterosis, Populations, Inbreds, Hybrids

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

20 points total

1. Explain Lonnquist’s selection study to improve yield of 2 maize inbreds using (a new technique at that time) convergent improvement. How does that study affect our 2 hypotheses (overdominance and dominance) for explaining inbreeding depression and heterosis?



2a. Diagram Gardner’s procedure of modified mass selection using blocks of 50 plants in a population of 1000.



2b. What is k (selection intensity) if you keep the best 10%?



2c. What is k for normal mass selection?



3a. In Lonnquist’s modified ear-to-row selection system, is selection on the male parent, female parent, or both?



3b. What is a composite pollenizer (CP), and why use one?



4. Describe the development of a cytoplasmic-genic hybrid production system for onion, including the development of the male-sterile female parent, the elite male parent, and the maintainer inbred.  Show genotypes and phenotypes of the inbreds involved.



5a. What kind of tester would provide a good estimate of specific combining ability for early testing of S0 individuals taken at random from an improved population: an inbred line, a single-cross hybrid, a 3-way hybrid, or a double-cross hybrid?





5b. How would you choose the particular cultivar to use as a tester in your program (from the many available in the type you gave as your answer to part a.)?



6. What are the advantages of using late (S6 lines) testing instead of early (S1 lines) testing for inbred line development in a cross-pollinated crop?



7. Contrast pedigree and modified pedigree (SSD) as methods for improving inbred lines of cross-pollinated crops for use in hybrid production.



8. Contrast the following 2 selection methods with regard to how the inbreds extracted from the recurrent selection process will be made into hybrids: recurrent selection with progeny testing using half-sib families vs. reciprocal half-sib family selection.



9. Which selection method would produce the most gain per year of the two shown below, A or B? Given: s2A = 27.4, s2P(I) = 11.6, s2P(HS) = 2.3, s2(FS) = 2.0, s2(S1) = 1.8

%       1        2       5       10      20       50
k      2.64     2.42     2.06     1.76     1.40     0.80

Method A
2012 Summer               Discard
–>     4000 plants     —–>  3960 plants
|        tested and        |
|       intercrossed       | Save 100
|    (before selecting)    | seeds each
|                          | of the best
————————–  40 plants
Method B
2012 Spring          Discard         2012 Summer
500             450 families      Intercross
families               ^              best 50
tested —-data——>|———> families(remnant
^                  |             seeds used)
|             2012 Winter            |
|         Store seeds from each      |
—– of 10 plants from each of <—
50 plots in summer block