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Third Phase in the Yield Evaluation of Synthetic Varieties of Maize¹

Nine synthetic maize (Zea mays L.) varieties, 36 variety crosses, and four single-cross hybrids were evaluated for yield at eight Corn Belt locations in six states. This is the third phase of a program for sequentially evaluating the yield potential of synthetic varieties developed as improved sources of breeding material. ‘Iowa Stiff Stalk Synthetic #2’ x ‘Pa. Intermediate Synthetic’ and ‘Iowa Stiff Stalk Synthetic #2’ x Iowa Long Ear Synthetic' were the high-yielding variety crosses. They approached the yield level for two of the single-cross hybrid checks. The stability parameters showed the regression coefficients to be siroilar, and the variety crosses had lower deviation mean squares. ‘Iowa Two-ear Synthetic’ was the highest-yielding variety per se, and Iowa Stiff Stalk Synthetic the lowest, which agrees with previous phases of testing. Iowa Synthetic #2 and ‘Tuxlan’ included exotic germplasm and yielded as well per se and in crosses as Iowa Stiff Stalk Synthetic. Midparent heterosis in the third phase was 14%.

Key Words: Zea mays L. • Population improvement • Maize breeding • Heterosis

² Research Geneticist, Plant Science Research Division, Agricultural Research Service, US Department of Agriculture, and the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50010, cooperating. Journal Paper No. J-6892 of the Iowa Agr. Home Econ. Exp. Sta., Project No. 1575.

Received for publication May 6, 1971.