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Mass Selection and Inbreeding Depression in Three Autotetraploid Maize Synthetics¹

Three autotetraploid maize (Zea mays L.) synthetics (B, CD, and OP) were evaluated to determine the effectiveness of mass selection for improved seed set and agronomic type, and to study inbreeding depression from one generation of self-pollination. S₀ populations of B(M)C0, B(M)C5, B(M)C11, B(M)C17, B(M)C21, CD(M)C0, CD(M)C3, CD(M)C7, CD(M)C11, CD(M)C14, OP(M)C0, OP(M)C4, OP(M)C8, OP(M)C12, and OP(M)C17 were evaluated in 1979 and1 980. S₀ and S₁ populations of B(M)C0, B(M)C11, B(M)C22, CD(M)C0, CD(M)C7, CD(M)C15, OP(M)C0, OP(M)C8, and OP(M)C18 were evaluated in 1981 and 1982. Visual mass selection improved seed set in B and OP, although a plateau appears to have been reached in the later cycles of selection. Significant increases in yield and ear height were found in B and OP, while days to flower and plant height increased in all synthetics. Inbreeding depression for seed set was small, suggesting seed set may not be the limiting factor in maintaining autotetraploid maize inbred lines that it is in other autotetraploid species. Inbreeding depression for yield corresponded to that expected based on the coefficient of inbreeding assuming the completely inbred generation has a mean of zero. Rates of inbreeding depression were similar to rates from other studies of autotetraploid maize. However, the rates of inbreeding depression for yield (g plant^–1) and ear length appear to be higher in autotetraploids than in diploids. No significant differences in rate of inbreeding depression between early and late cycles of selection were found.

Key Words: Zea mays L. • Seed set • Corn breeding

² Former graduate research assistant (now graduate assistant, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011) and professor of plant genetics, Dep. of Agronomy, Univ. of Ill., Urbana, IL 61801.

Received for publication July 25, 1983.