The history of the potato is instructive. The wild varieties that the first South American human settlers discovered (dates vary but > 14,000 years ago probably) were toxic, but if eaten with a small amount of clay, were discovered to be edible. Andean peoples didn't stop there however: they began breeding less toxic varieties of potato (there are now ~ 4000 cultivars) which also was a process of experimentation and selection of optimal results over a long time period. Breeding of maize followed a similar experiment-and-select process.
As far as why the architects of European colonialism wanted to deny that native peoples had such capabilites, well:
> "In a secularizing world, infantilization quickly became a moral posture and a theological necessity. It allowed the main actors in slavery and colonialism to make peace with their own consciences, and the intelligentsia and the Church to produce a powerful mix of justifications for the new world order. It allowed glib talk of the historical necessity to care for the retrogressive, irrational, ignorant savages and the Christian responsibility to guide them towards a better future."
As far as why the architects of European colonialism wanted to deny that native peoples had such capabilites, well:
> "In a secularizing world, infantilization quickly became a moral posture and a theological necessity. It allowed the main actors in slavery and colonialism to make peace with their own consciences, and the intelligentsia and the Church to produce a powerful mix of justifications for the new world order. It allowed glib talk of the historical necessity to care for the retrogressive, irrational, ignorant savages and the Christian responsibility to guide them towards a better future."
https://newint.org/features/2007/10/01/roots/