Comparison of half-sib and full-sib reciprocal recurrent selection and their modifications in simulated populations

Haif-sih and full-sib reciprocal recurrent selection (RRS) have been successful methods of reciprocal improvement of two maize (Zca mays L.) populations to maximize the performance of the population cross. The objective of our study was to use computer simulation to compare responses to selection of populations themselves and their crosses for half-sib and full-sib RRS and one modification. The modification included an additional generation of inbreeding before producing testcrosses (S 2 plants as recombination units). Parental populations included 110 individuals throughout 20 cycles of selection. Evaluation of each individual in both RRS methods was based on the mean performance of 10 testcross progeny. Selection intensity was 10% in all instances. Assumptions for the simulation studies included diploid individuals with two alleles per locus, where expression of the quantitative trail was determined by 40 independent loci; genotype x environmental interaction was not included. There were 22 initial conditions corresponding to two sets of initial parental population allele frequencies and 11 genetic models. The two sets of initial parental populations were equal and unequal allele frequencies. The 11 genetic models included additive genetic variance, three levels of dominance, and seven epistasis combinations. Half-sib and full-sill RRS and their modification were simulated for each of the 22 initial conditions with three replications of each condition for 20 cycles of RRS selection. Genetic response of full-sib RRS was similar to half-sib RRS for 21 initial conditions with S 1 s as the recombination units. The linear response of half-sib RRS was 1.7 times (P ≤ 0.01) greater than full-sib RRS for the genetic model that included complete dominance and dominance x dominance epistasis with S 1 recombination units. There were no significant differences between half-sib and full-sib RRS with S 2 s as recombination units but use of S 2 s increased selection response for both half-sib and full-sib RRS. Compared with half-sib RRS, full-sib RRS requires 50% fewer test-crosses, but full-silo RRS has the same selection response as half-sib RRS. Full-silo RRS with S 2 s as the recombination units would lie the more efficient method of interpopulation improvement in maize breeding.