Since problems and objectives in the production of disease-resistant varieties of potatoes are not confined to a single State but involve large regions of the country, potato breeding was organized in 1929 as a national project. The work is conducted cooperatively by 35 State experiment stations and the Department. The practice under the program is to send seedlings produced by the Department or by any of the cooperating State experiment stations to other States for trial. After sufficient tests, if any seedling variety shows superiority to the standard varieties in at least one important character, such as yield, market quality, or resistance to a disease that is difficult to control, it is named and released to growers. Since 1932 more than 25 varieties have been released. Several of these have increased rapidly in yearly production; others increased more slowly.

In some of the new varieties the important objective for which they were bred has been reached. Sebago, Empire, Placid, Virgil, Chenango, and Ashworth are resistant to late blight; Menominee, Ontario, Cayuga, and Seneca are resistant to common scab; Katandin, Chippewa, Warba, Houma, Earlaine, Sebago, Red Warba, Mohawk and Menominee are resistant to one or more virus diseases; and Teton is resistant to ring rot.

How well the new varieties have been received by the growers is shown by the fact that in 1945 about 26 percent of all the certified seed in the United States consisted of varieties that have been released since 1932. None of these will meet the needs of the growers in all the cooperating States, and it is doubtful if such an ideal variety will soon be produced. However, a sectional demand existed for each one, and because of their disease resistance and other characters of economic importance they have been increased under severe competition and critical evaluation.

A beginning has been made, and the new varieties that have already been released have been a factor in increasing the yield of potatoes in the United States from a little more than 100 bushels an acre 25 year, ago to about 150 bushels an acre in 1945. The results indicate much greater possibilities in breeding. We have available a large number of important characters that have not yet been combined in one variety, and each new combination should give us a new variety more valuable to some of the growers than any we now have. These characters include wide adaptation; early, medium, and late maturity; smooth, desirable shapes; shallow eyes; high yielding ability; and high dry-matter content. Besides, we have seedlings that resist one or more of the following diseases and insects: Mild mosaic, latent mosaic, rugose mosaic, leaf roll, net necrosis, yellow dwarf, late blight of the vines, tuber rot initiated by the late blight fungus, common scab, potato wart, brown rot, ring rot, hopperburn, flea beetle injury, and aphid injury.

THE AUTHORS

F. J. Stevenson is a geneticist in the Bureau of Plant Industry, Soils, and Agricultural Engineering, where he conducts research in potato breeding with special emphasis on the inheritance of disease resistance in potatoes. Before joining the Department in 1930, Dr. Stevenson was successively an instructor in plant genetics at State College of Washington, and assistant professor at the University of Minnesota, College of Agriculture. He is a graduate of the State College of Washington.

Robert V. Akeley is a plant breeder in the Bureau of Plant Industry, Soils, and Agricultural Engineering. His work deals with potato breeding and genetics with special reference to color, dry-matter content, yield, and disease resistance.