As I understand it, the idea is to have two parent lines that when produce the desired traits in heterozygous offspring but not in second-generation offspring. Sort of a Mendelian DRM.
This is incorrect. As I already stated: the cross-breeding is to take advantage of hybrid vigor[1], it is not an effort to intentionally hamper successive generations. This same practice occurs in non-GMO, non-patented plant breeding, and has been done for over a hundred years[2]
1: https://en.wikipedia.org/wiki/Heterosis 2: https://en.wikipedia.org/wiki/History_of_plant_breeding#Gree...