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Correlated Responses of Yield and Other Agronomic Traits to Recurrent Selection for Stalk Quality in a Maize Synthetic¹

Changes in plant, ear, and grain traits after three cycles of S₁ recurrent selection for resistance to Diplodia stalk rot (SR) and mechanical stalk breakage (MS) were evaluated in the BSI maize (Zea mays L.) synthetic. The cycle populations (BS| and C1 C3 for BSISR and BSIMS for stalk-rot and stalk-strength selection, respectively), populations crossed to a single-cross tester, and crosses between populations of each procedure of selection were evaluated in replicated experiments in 1980 and 1981. The two procedures of selection gave contrasting responses in plant traits. The BSIMS populations showed increased plant height, internode number and length, and delayed anthesis, whereas the BSISR populations showed a trend toward earlier anthesis, with reduced plant height and internode length. Most of the changes for plant traits occurred during the initial cycle of selection when there was no control on flowering date of selected S_l lines. Grain yield was reduced from 7.08 t ha^–l in BSI to 4.95 and 5.42 t ha^–1 in BSIMSC3 and BSISRC3, respectively. Although the population crosses also showed significant yield reductions, they yielded higher than either parent. No significant yield change was observed in testcross performance. All yield components except kernel weight also were reduced by both selection procedures. Ear diameter and length, however, had the highest correlations with yield and contributed most to yield reductions observed in the improved populations for stalk quality. Thus, mild selection should be practiced for yield and other agronomic traits of importance when undertaking a population improvement program for stalk quality.

Key Words: S₁ selection • Stalk rot • Stalk lodging • Selection responses

² Former graduate student, now maize breeder with Garst Seed Co., Research Dep., Ames, IA; professor of plant breeding, Iowa State Univ., Ames, IA 50011.

Received for publication November 10, 1983.