Effects of two-locus linkage disequilibrium on progress from reciprocal recurrent selection in maize.

Because each population in a reciprocal recurrent selection program can be dually described as a tester for its reciprocal and as a population subject to selection, selection progress can be partitioned into algebraic terms that are (a) unaffected by initial linkage disequilibrium, (b) modified exclusively by initial linkage disequilibrium in the selection populations, (c) influenced solely by initial linkage disequilibrium in the tester populations, and (d) modulated jointly by initial linkage disequilibrium in both populations. If only additive genetic effects are present in the intercross population, linkage disequilibrium affects selection progress via only the selection populations. Initial linkage disequilibrium affects selection progress via the tester populations, and/or the selection and tester populations jointly, only in the presence of epistatic effects for which, out of all alleles involved in the interaction, two alleles emanate from the tester population. If only additive x additive epistasis is present, initial linkage disequilibrium affects progress via both the selection and tester populations, but the effect is permanent via only the selection populations. The effect of initial linkage disequilibrium via the tester populations, and/or the selection and tester populations jointly, is permanent only in the presence of additive x dominance and/or dominance x dominance epistasis in the intercross population.