Plant breeders use different methods depending on the mode of reproduction of crops, which include:
Self-fertilization, where pollen from a plant will fertilise reproductive cells or ovules of the same plant
Cross-pollination, where pollen from one plant can only fertilize a different plant
Asexual propagation (e.g. runners from strawberry plants) where the new plant is genetically identical to its parent
Apomixis (self-cloning), where seeds are produced asexually and the new plant is genetically identical to its parent