Genotype versus phenotype. Look these up if you don't remember them. Another reason that self-compatibility is good is that in many crops it is hard to get good fertilization. Asexual reproduction Another method that is especially useful for humans. The plants produced are genetically identical to the parents.
All resultant plants are part of a clone.
Grafting is an asexual technique that is widely used. Mutation is the original source of genetic variation. Sexual recombination is the mechanism for maintaining it. Pieces in new genetic backgrounds. Sometimes small pieces get lost in shuffle.