Progress in Conventional Plant Breeding

Grain yields of wheat, maize, sorghum and soybeans have increased continually since 1930. Variety improvement has been responsible for 50% or more of the yield increase for each crop. Genetic improvements in yield potential have increased linearly for the past 25 years and show no sign of leveling off, for any crop. Improved varieties of the cereal grains: wheat, maize and sorghum, have in part been superior because they were able to efficiently utilize increased amounts of commercial nitrogen fertilizer. Increased yield potential of new varieties of all four crops generally is due to improvements in defensive traits such as standability, heat and drought tolerance, and pest resistance. Inheritance of the improved traits is usually genetically complex and is not well understood either in genetic or physiological terms. A list of most needed genetic improvements in new varieties will include such things as improvements in yield potential, stress tolerance, and pest resistance. Until the genetics and physiology of these traits are better understood it will be difficult for biotechnology to make major direct contributions to plant breeding. However biotechnology can make many useful small contributions to plant breeding at the present time and eventually it also will provide major assistance in explaining the genetics and physiology of important traits.