With those events, the only thing remaining to get the seed industry going was legal protection. “The first federal law aimed at protecting agricultural intellectual property was the Plant Patent Act (PPA) of 1930. At the time that passed, and in the understanding of science of the day, it was believed that plants couldn’t be patented.
So when the PPA was passed it was limited to asexually-reproducing plants (those that reproduce by cutting or grafting). It wasn’t until 1970 that the Plant Variety Protection Act (PVPA) was passed basically to fill a gap left by the PPA. The Plant Variety Protection Act was aimed at sexually-reproducing plants and it granted patent-like protection to them.
More recently, utility patents were granted for living organisms and plants. The Supreme Court has confirmed that with advancements in technology plants and living organisms can be patented.