RA 00110.pdf - OAR@ICRISAT

What Does the Future Hold
The authors believe that in maize S, per se will
improve the variety cross as fast in early cycles (say
15 or 20) as RFS. However, RFS should result in a
higher ultimate selection limit for the variety cross as
shown in Figure 6. The results of the study just
reported indicate that different genetic mechanisms
are involved with the two methods. S, line per se
seems to be improving the variety cross through
changes involving loci that exhibit additive effects,
while RFS seems to involve more of the nonadditive
effects as expected from theory.
Continued selection based on selfed progeny may
gradually reduce dominance effects. This has apparently
occurred in crops that are largely self-pollinated.
The corollary to this would be that if reciprocal
recurrent selection were practiced between two populations
of soybeans [Glycine max (L.)], or wheat
[Triticum aestivum (L.)], or other self-pollinated
crops, perhaps dominance relationships would gradually
increase with a corresponding increase in
heterosis. The heterosis presently seen in those crops
is most likely due to additive x additive epistasis
since inbreeding depression does not accompany the
observed heterosis.
Summary
The advantages and limitations of different methods
of intrapopulation and interpopulation selection
systems have been examined and the consequences
of effective population size, selection intensity, and
genotype * environment interaction discussed. Experimental
evidence from a comparison of S 1 line
versus reciprocal full-sib (RFS) selection in three
populations of maize indicates that both were effective
in increasing variety cross performance. But
although S 1 was better at increasing self- and
random-mated population yields, it is postulated
that higher-yielding variety crosses ultimately would
result from RFS.
References
Compton, W.A., and Lonnquist, J. 1982. A multiplicative
selection index applied to four cycles of full-sib recurrent
selection in maize. Crop Science 22:981-983.
Comstock, R.E. 1979. Inbred lines vs. the populations as
testers in reciprocal recurrent selection. Crop Science
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Comstock, R.E., Robinson, H.F., and Harvey, P.H. 1949.
A breeding procedure designed to make maximum use of
both general and specific combining ability. Agronomy
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Hallauer, A.R., and Miranda, J.B. 1981. Quantitative
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Hill, W.G., and Robertson, A. 1966. The effect of linkage
on limits to artificial selection. Genetical Research 8:269-294.
Jones, L.P., Compton, W.A., and Gardner, C O . 1971.
Comparisons of full- and reciprocal recurrent selection.
Theoretical and Applied Genetics 41:36-39.
Rai, K.N., and Andrews, D.J. 1984. Inbreeding depression
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Ross, W . M . , and Gardner, C O . 1985. The mechanics of
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Pages 8-38 in Proceedings of the Plant Breeding Methods
and Approaches in Sorghum Workshop for Latin America,
11-16 Apr 1983, Mexico Pt. 1. Londres, Mexico: Centro
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Subandi, Compton, W.A., and Empig, L.T. 1973. Comparison
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two variety crosses of corn. Crop Science 13:184-186.
Thomas, M . A . 1979. Replicated S 1 line per se and reciprocal
full-sib selection compared in maize (Zea mays L.).
Ph.D. thesis, University of Nebraska, Lincoln, Nebraska,
USA.
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