The seeds produced are often plantable. For many seeds, especially GMO seeds, the grower needs to acquire a license to the seeds and agrees not to save seeds f

The seeds produced are often plantable. For many seeds, especially GMO seeds, the grower needs to acquire a license to the seeds and agrees not to save seeds from planted crops (as you suspect, to ensure income for the seed producer). Other seeds are patented varieties. Typically these are 'hybrids' which are a cross of two varieties of the same plant for whatever specific features they select. These seeds won't 'breed true' so the offspring will likely not be identical to the parents. From what I understand, GMO crops won't have a very stable lineage. Nature tends to select against the genetic modifications, but I do believe most GMOs are replantable today. This is not the case for GMO salmon, which they are trying to sterilize.