Plant Breeding Methods (CS, GN, HS
741)
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, s2(FS) = 2.0, s2(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
2000 Summer Discard
--> 4000 plants -----> 3960 plants
| tested and |
| intercrossed | Save 100
| (before selecting) | seeds each
| | of the best
-------------------------- 40 plants
Method B
2000 Spring Discard 2000 Summer
500 450 families Intercross
families ^ best 50
tested ----data------>|---------> families(remnant
^ | seeds used)
| 2000 Winter |
| Store seeds from each |
----- of 10 plants from each of <---
50 plots in summer block
