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Evaluation of the Performance and Combining Ability of Selected Lines Derived from Improved Maize Populations¹

Seven cycles of reciprocal recurrent selection for grain yield were completed in maize (Zea mays L.) populations ‘Iowa Stiff Stalk Synthetic’ (BSSS) and ‘Iowa Corn Borer Synthetic No. 1’ (BSCB1). Also, seven cycles of recurrent selection based on half-sib progeny performance and one cycle based on S2 line performance have been completed for BSSS. Populations BSSS(R)C5 and BSCB1(R)C5 were crossed and random-mated to give BS6. Then, BS6 had two cycles of recurrent selection based on half-sib progeny performance. Crosses of the improved populations and four selected S2 lines from each improved population crossed in design II's (six sets) were evaluated for grain yield and moisture and for root and stalk lodging. The average yields for four sets of S2 crosses were not significantly different from their respective population crosses; one set of S2 crosses yielded significantly less than its population cross, BSSS(R)C7 x BS6(RS)C2; and one set of S2 crosses yielded significantly higher than its population cross, BSCB1(R)C7 xBS6(RS)C2. Generally, sets of crosses had less grain moisture and better resistance to root and stalk lodging than did their respective population crosses. General combining-ability effects accounted for 76% of the total genetic variation for yield among S2 x S2 line crosses. Compared with five single-cross checks, no S2 x S2 line cross yielded as well as the highest-yielding check, but one had a performance index equal to the best check, and several had performance indices similar to four checks.

Key Words: Zea mays L. • Recurrent selection • General and specific combining ability

² Former graduate assistant, now corn breeder with DeKalb-Pfizer Genetcs, North Liberty, Iowa; professor of plant breeding; and research geneticist (USDA), Iowa State Univ., Ames, IA 50011. (assistantship for G.R. Stangland funded by Pioneer Hi-Bred Int.)

Received for publication August 12, 1982.