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Relationships among Seedling and Mature Root System Traits of Maize¹

Maize (Zea mays L.) breeders often have resorted to various techniques, which measure root strength or type, in an effort to select for decreased root lodging. Seedling root traits of S₁ lines selected for high and low mature root-pulling resistance in the field from C0 and C8 cycles of Iowa Stiff Stalk Synthetic [BSSS(R)] and Iowa Corn Borer Synthetic #1 [BSCB1(R)] were studied in a preliminary experiment. Also, we used 90 S₁ lines from each of the C0 and C8 cycles of BSCB1(R) to estimate genetic parameters for seedling root-pulling resistance.

Estimates of heritability for seedling pulling resistance were 0.56 ± 0.15 and 0.42 ± 0.16 for 90 random S₁ lines from each of the C0 and C8 cycles of BSCB1(R). Predicted genetic advance was 0.7 kg/plant for BSCB1(R)C0 and 0.6 kg/plant for BSCB1(R)C8. Estimates of S₁ line x environment interactions for seedling pulling resistance of selected, low and high lines from C0 and C8 cycles of BSCB1(R) were not significant when measured in two greenhouse environments. Rank and genotypic correlation coefficients, however, between seedling root-pulling resistance and mature rootpulling resistance measured at two dates and between seedling pull and lodging were small (all r-values were lower than 0.33). Selection differentials for root pulling resistance at any stage suggested that selection would be more effective in discarding lodging-susceptible lines than in identifying those with superior lodging resistance. We have concluded that selection for high seedling root pulling resistance has limited utility in improving mature root strength of these populations.

Key Words: Zea mays L. • Selection advance • Heritability • Population improvement • Recurrent selection • Root pulling resistance

² Maize physiologist at Tohoku. Natl. Agric. Exp. Stn., Morioka, Iwate, Japan, and visiting scientist at Iowa State Univ. from 1981 to 1982; and former assistant professor, Dep. of Agronomy, Iowa State Univ., Ames. IA 50011; now director of research, Garst Seed Co., Coon Rapids, IA 50058.

Received for publication March 1, 1982.