Many types of polyploids are sterile. Polyploids are usually larger than diploids etc. This process often occurs by chance and humans have taken advantage of the rare plants in which it occurred. Geographic variation in plants Humans usually want uniform plants, but in nature just the opposite is favored. Variable offspring tend to have better survival.
Humans provide a more or less uniform environment and enough care to make sure crops survive.
In nature, gene frequencies vary in populations of plants over geographic distance. At some point, limits in how much the plant can tolerate are reached and this helps to define the range of a plant. These same things are true for crop plants, but people can help the crop avoid some otherwise limiting factors. Originally, crop plants may have been restricted by oceans, mountains, and deserts. Humans have transported many of them where they would not have gone naturally.