RA 00110.pdf - OAR@ICRISAT

Table 4a. Prediction equations, advantages, and disadvantages for intrapopulation improvement using mass selection.
Prediction equation:
Mass Selection 1
for selection
after pollination.
or
Mass Selection 2
for selection prior
to pollination.
Time per cycle -1 year
Advantages
Disadvantages
1.
2.
3.
4.
1.
2.
3.
4.
Can maintain large Ne.
Selection intensity can be high so that the selection differential can be large.
No yield trial plots, inexpensive.
Simple to conduct.
If heritability of selected trait is very low, progress may be difficult.
Requires isolated plots.
Cannot apply usual types of selection indices.
High population densities may not work well.
= variance among half-sib families =1/4
= variance among full-sib families = 1 / 2 +
1/4
= plot-to-plot environmental variance or family x
replication interaction
= plant-to-plant environmental variance
r = number of replications
n = number of plants per plot
= genetic variance among S 1 or S 2 lines
= total genetic variance at S, or S 2 level
of inbreeding
The advantages and disadvantages of each method
are outlined in Table 4.
Interpopulation Improvement
In interpopulation improvement the breeding objective
is to improve the performance of the population
cross. Any of the population improvement schemes
may also improve intrapopulation (variety) crosses,
but it is logical that if the interpopulation cross is to
be improved, selection should be based on cross
performance because it is then a direct rather than an
indirect response to selection. Following that line of
reasoning, Reciprocal Recurrent Selection was suggested
by Comstock et al. (1949). Their idea was to
use cross-bred, half-sib families (as described for
half-sib 1 in Table 4b with the other population used
as the tester and vice versa).
Reciprocal Half-Sib Selection ( R H S )
Individual plants from population A are self-pollinated
and also crossed to several plants from population
B. The crossed seed is bulked to form one
entry for testing. Population B individuals are also
selfed and crossed to several plants from population
A. Thus, two sets of half-sib families are produced. If
100 entries are to be tested from each population a
total of 200 are grown. If 20 is judged to be a reasonable
effective population size (N e ), then a 20% selection
intensity will result in the selection of 20 from
100 in each variety.
Reciprocal Full-Sib Selection ( R F S )
A more recent interpopulation scheme used for a
number of years at Nebraska in maize is reciprocal
full-sib selection. As populations of maize have been
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