Why did genetically varied land varieties provide useful material for early pure-line selection?

Genetically varied land varieties were essential to early pure-line selection because they served as a rich, pre-existing reservoir of diverse genetic material.1

During the early 1900s, these land varieties—which are local populations adapted to specific geographic regions and characterized by high genetic diversity—contained numerous superior individual plants waiting to be identified and exploited. Because these populations were not uniform, breeders could select the most promising individuals from them to develop new, high-performing pure-line varieties. This method relied on the natural variation already present within these crops, allowing breeders to isolate and propagate superior strains that were often more productive than the original mixed populations.21