Farmers have long relied on genetic diversity to breed new crops, but in the early 1900s scientists began to study the importance of plant genetic diversity for agriculture. Scientists realized that seed crops could be systematically bred with their wild relatives to incorporate specific genetic traits or to produce hybrids for more productive crop yields. The spread of hybrids led to less genetically diversity than normal plant populations, however, and by 1967, plant scientists led an international movement for conservation of plant genetic resources through the United Nations's Food and Agricultural Organization, and later through the Consultative Group for International Agricultural Research, both of which are headquartered in Europe. To conserve plant genetic resources, researchers must collect and store plant germplasm-the genetic material required to propagate a plant-usually in the form of a seed.