Plant Breeding Methods (CS, HS 541)

Exercise 6 – Recurrent Selection, Gain, Synthetics

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

20 points total

1. 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? Why?


1b. 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.)?


2. 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?


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


4. 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.


5. 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, s2P(FS) = 2.0, s2P(S1) = 1.8;

and k for selection percentage: 1%=2.64, 2%=2.42, 5%=2.06, 10%=1.76, 20%=1.40, 50%=0.80.

Method A
         2011 Summer               Discard
 -->     4000 plants     ----->  3960 plants
|        tested and        |
|       intercrossed       | Save 100
|    (before selecting)    | seeds each
|                          | of the best
 --------------------------  40 plants
Method B
   2011 Spring          Discard         2011 Summer
      500             450 families      Intercross
    families               ^              best 50
     tested ----data------>|---------> families(remnant
        ^                  |             seeds used)
        |             2011 Winter            |
        |         Store seeds from each      |
         ----- of 10 plants from each of <---
               50 plots in summer block