RA 00110.pdf - OAR@ICRISAT

these two methods has been undertaken at Nebraska.
Three base populations, called S 0 , B 0 , and K 0 are
shown in Figure 3. From these, replicate subpopulations
were created using either RFS or S 1 line per se
selection as shown in Figure 4. The replicates are
continued independently of each other and provide
an error term for comparing breeding methods.
Some drift is likely among these replicates because
only 10 S, lines are selected for recombination in
each cycle. Five cycles of selection are now completed
in this study, but evaluation is not yet complete.
The responses reported here were originally
reported by Thomas (1979) and cover the first two
cycles with very extensive evaluation.
The cycles of S 1 per se and RFS selection were
tested as bulked inbred populations, as random
mated populations, and in variety crosses. By selfing
100 or so plants and bulking seed from them, an
inbred population would be formed that could then
be tested to measure the direct response to S 1 per se
selection and an indirect response to RFS selection.
Similarly, the variety crosses were used to measure
the direct response to RFS and the indirect response
to S 1 per se selection. The random-mated populations
not only permitted the evaluation of each type
of selection for intravarietal improvement but also
allowed the calculation of changes in heterosis and
inbreeding depression.
The selection criterion used is an index of yield (kg
ha -1 ) multiplied by the proportion of upright plants
and the proportion of plants without dropped ears.
This produces a value best called machine harvestable
yield ( M H Y ) calculated from hand harvested
data:
Index
( M H Y ) =
Yield
adjusted to
15.5%
moisture
Proportion
x upright x
plants
Proportion
plants
without
dropped ears
This index has been applied to all of the family
selection studies at Nebraska for some years with
apparent success [cf. Subandi et al. (1973), Compton
and Lonnquist (1982)].
The experiment was conducted with five replications
in two watering treatments at two locations in 2
Figure 4. Subpopulations (relicates) formed by two cycles of S 1 line per se selection and 2 cycles of R F S
selection in the B, S, and K populations. — = generations advance, — = testcross.
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