crossbred

Some people have grown crossbred seed, and it’s possible that the resulting higher amounts of chlorophyll result in a somewhat darker plant.

Certainly so in many cases, but it's not difficult to imagine strains for mass consumption hobbled by proprietary sequences that cause the plants to wither without a certain additive or activate some kind of DNA-destruction process if not crossbred with another secret strain.

Even wolves that have been crossbred over several generations with dogs to get a more wolflike appearance tend to be exceptionally difficult to manage, have been well-known to attack other pets, can be very destructive, and ultimately most people want them because of how they look.

For instance the modern Irish Wolfhound was created by an nobleman who, worried about the breed dying out (there hadn't been a wolf in GB in over a hundred years), bought every wolfhound he could get his hands on, and crossbred them with mastiffs and Danes to build up a healthier population (while maintaining stature).