Starting largely in the .1930s, open-pollinated corn varieties were replaced by hybrid corn varieties. The pollen source is not controlled in open-pollinated varieties, so no two plants of a variety are likely to be identical in genotype or performance characteristics. Hybrids rapidly replaced open-pollinated varieties when hybrids were developed that had consistently superior performance (largely yield) characteristics (Griliches 1957, Dixon 1980).
This paper was published in Huffman, W. E. "The Role of the Public Sector in Corn Inbred Line Development." Iowa State University, Department of Economics, Staff Papers Series 146 (1984).
Huffman, Wallace E., "The Role Of The Public Sector In Corn Inbred Line Development" (1984). Economic Staff Paper Series. 38.