Turnip (Brassica rapa L. ssp rapifera Metzg.) population improvement and cultivar production

In 1977, a fodder turnip breeding programme was started from seven cultivars with the primary aim of increasing dry-matter yield. The breeding method chosen was population improvement by half-sib family selection on a biennial cycle. Seed production in polythene tunnels with blowflies as pollinators was followed by assessing the resulting progenies in replicated yield trials and observation plots from which plants were selected for the next cycle. Six generations of selection resulted in a population with a yield that was 25% higher than the mean of the initial seven cultivars. This was remarkably close to the predicted superiority of the population, despite a significant discrepancy in one generation. It is concluded that the greatest response to selection per year would be achieved by selecting eight families from 128 assessed for 1 year in trials at two or three sites with an overall total of six replicates, given a resource limit of 800 plots.