Estimates on the current status of the U.S. corn germ plasm base were made by comparing the use of publicly developed lines as parents in 1974 U.S. hybrid seed production with previous surveys made during the past two decades on the use of public lines. All surveys were conducted by the American Seed Trade Association. Fifty-seven percent of the 1.2 billion pounds of hybrid seed covered by the 1975 survey involved one or more public lines used as parents in hybrid seed production. The 7 percent increase over the 40 to 50 percent use of public lines shown in the three previous surveys is not believed to be of sufficient magnitude to have an effect on the current germ plasm base. Parental sources of new inbred line development were equally distributed among hybrids involving adapted parental lines, exotic crosses, synthetics and populations improved by cyclic selection. If the use of hybrids involving adapted lines had been large, it would suggest a narrowing of the germ plasm base, but these results indicate no great shift in either direction. The three inbred lines A632, Mo 17 and B37 were used as parents in hybrids that produced seed sufficient to plant 15 .2, 7 .0 and 6.8 percent of the 1975 corn acreage, respectively. The large-scale usage of a few lines would tend to narrow the corn germ plasm base. Normal cytoplasm was used in 87 percent of the total hybrid seed production covered in this survey. If normal cytoplasms are more alike than different, their continued widespread use might contribute to a potentially narrower germ plasm base. Suitable methods are badly needed for characterizing cytoplasms other than by sterility and fertility restorer responses. The survey showed the male sterile Texas cytoplasm was not being used, while 6.7 and 1.2 percent, respectively, of the C and S cytoplasm was indicated as being used in hybrid seed production.

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