Zusammenfassung
According to quantitative genetic theory, linkage disequilibrium (LD)
can hamper the short- and long-term selection response in recurrent
selection (RS) programs. We analyzed LD in two European flint maize
populations, KW1265 x D146 (A x B) and D145 x KW1292 (C x D), under
modified recurrent full-sib selection. Our objectives were to
investigate (1) the decay of initial parental LD present in F-2
populations by three generations of intermating, (2) the generation of
new LD in four (A x B) and seven (C x D) selection cycles, and (3) the
relationship between LD changes and estimates of the additive genetic
variance. We analyzed the F-2 and the intermated populations as well as
all selection cycles with 104 (A x B) and 101 (C x D) simple sequence
repeat (SSR) markers with a uniform coverage of the entire maize
genome. The LD coefficient D and the composite LD measure Delta were
estimated and significance tests for LD were performed. LD was reduced
by intermating as expected from theory. A directional generation of
negative LD between favorable alleles could not be observed during the
selection cycles. However, considerable undirectional changes in D were
observed, which we attributed to genetic sampling due to the finite
population size used for recombination. Consequently, a long-term
reduction of the additive genetic variance due to negative LD was not
observed. Our experimental results support the hypothesis that in
practical RS programs with maize, LD generated by selection is not a
limiting factor for obtaining a high selection response.
Nutzer