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Semi-dwarf, high-yielding varieties of wheat and rice, along with associated inputs, have formed the basis of what has popularly been known as the “green revolution” in many developing nations. This report traces the development and use of comparable semi-dwarf varieties in the United States. It is the first general publication on the subject. Particular attention is given to the important role played by foreign varieties, especially those generated by international agricultural research centers, in the improvement of wheat and rice in the United States. Neither crop is indigenous to the United States so that all the ancestors of present varieties have been “immigrants.” The genetic source of semi-dwarfism is usually the same for both the U.S. varieties and those in developing nations. The report covers the following main subjects: history of production and varietal improvement, development and use of semi-dwarf wheat, development and use of semi-dwarf rice, associated technological factors, changes in yields, evaluating economic impact, and institutional linkages. By late 1979, 147 semi-dwarf varieties of wheat and 6 of rice had been released. Many of these included varieties developed in the international centers in their ancestry. Semi-dwarf wheat was planted on about 22 percent of the U.S. wheat area in 1974 and roughly 29 percent in 1979. Semi-dwarf rice varieties represented about 9 percent of the U.S. rice area in 1979. The semi-dwarfs have represented an evolutionary rather than revolutionary change. Their use is likely to expand.


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