Final answer:
Plant breeding has transformed from primitive selective breeding to advanced genetic engineering, resulting in improved crop varieties with desirable traits and involving a complex agricultural system.
Step-by-step explanation:
The field of plant breeding has evolved significantly from its early days when it occurred rather unintentionally, as primitive agriculturalists selected and propagated plants with desirable traits. Over centuries, this led to a gradual genetic modification through selective breeding. As the understanding of plant genetics improved, especially the sexual reproduction processes, advances in genetic engineering accelerated the development of novel traits in plants. The advent of genetic modification technologies over the last century has greatly expanded the possibilities in plant breeding, enabling the creation of crops with enhanced yield, disease resistance, and other beneficial qualities. Today, crop improvement involves a complex system intertwining farmers, seed producers, researchers, and various other stakeholders in the agriculture industry.