Quantitative traits having low heritability are improved by using

Quantitative traits having low heritability are improved by using recurrent selection.
Recurrent selection means repeated cycles of selection and breeding aimed at gradual genetic improvement of a few key traits in a single species.
Genomic selection and marker-assisted recurrent selection have been applied to improve quantitative traits in many cross-pollinated crops.
The benefits of breeding are cumulative in that each cycle or generation of improvement builds upon advances made in prior generations.