Those who save seeds are automatically considered plant breeders. A seed saver will choose desirable traits to pass along to future generations.
These would include taste, size, yield, disease resistance, etc. This act of selection is what makes one a breeder.
What is Plant Breeding From National Association of Plant Breeders
Plant breeding uses principles from a variety of sciences to improve the genetic potential of plants. The process involves combining parental plants to obtain the next generation with the best characteristics. Breeders improve plants by selecting those with the greatest potential based on performance data, pedigree, and more sophisticated genetic information. Plants are improved for food, feed, fiber, fuel, shelter, landscaping, eco-systems services and a variety of other human activities.
Plant breeding is the science-driven creative process of developing new plant varieties that goes by various names including cultivar development, crop improvement, and seed improvement. Breeding involves the creation of multi-generation genetically diverse populations on which human selection is practiced to create adapted plants with new combinations of specific desirable traits. The selection process is driven by biological assessment in relevant target environments and knowledge of genes and genomes. Progress is assessed based on gain under selection, which is a function of genetic variation, selection intensity, and time.
Other Published Definitions
“Plant Breeding is the art and science of the genetic improvement of plants.” – Fehr, Principles of Cultivar Development: Theory and Technique, 1987
“Plant Breeding is the art and science of changing the traits of plants in order to produce desired characteristics.” – Sleper and Poehlman, Breeding Field Crops, 1995
“Plant Breeding is the genetic improvement of plants for human benefit.” – Bernardo, Breeding for Quantitative Traits in Plants, 2010