In plant breeding, undesirable linkages can be broken by

In plant breeding, undesirable linkages can be broken by Recurrent selection, Disruptive mating, and Diallele, selective mating.
Recurrent selection means repeated cycles of selection and breeding aimed at the gradual genetic improvement of a few key traits in a single species.
Disruptive selection with assortative mating can lead to two reproductively isolated populations, but with random mating, it can lead only to polymorphism; the population will never diverge into two genetically isolated populations.
A diallel cross is a mating scheme used by plant and animal breeders, as well as geneticists, to investigate the genetic underpinnings of quantitative traits.