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Harvest index analyses in three improved maize synthetics^*

A.D. Novoa; W.A. Russell

Joint contribution: USDA-ARS and Journal Paper No. J-12938 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA. Project No. 2778. Send correspondence to W.A.R., Department of Agronomy, Iowa State University, Ames, IA 50011, USA.

ABSTRACT

Recurrent selection based on S₁ progeny evaluations was used to improve pest resistance in three maize (Zea mays L.) synthetics. five cycles were used in BS9 to increase resistance to the European corn borer (Ostrinia nubilalis Hübner) for the whole life of the plant; four cycles were used in BSAA and BSBB to increase resistance to both Diplodia (Diplodia maydis (Berk.) Sacc.) stalk rot and leaf feeding by first-generation European corn borer. The objective of this research was to evaluate the original and improved populations for correlated changes in important agronomic traits. For BS9, total plant yield decreased 2.78 Mg/ha from the CO to C5, stover weight decreased 0.91 Mg/ha, and grain yield decreased 1.86 Mg/ha. The harvest index decreased 3.8 percentage units from the CO to C5. Testcrosses of the cycle populations did not show significant changes. BSAA had a decreased total yield of 2.02 Mg/ha from the CO to C4, stover weight decreased 0.92 Mg/ha, and grain yield decreased 1.10 Mg/ha. There was no significant change for harvest index. In BSBB, there were no significant changes for yield traits. Testcrosses of BSAA and BSBB and also population crosses, BSAA x BSBB, showed no significant changes. Consequently, correlated changes in agronomic traits with recurrent selection for resistance to either European corn borer or Diplodia stalk rot may not be similar among different maize synthetics.

Keywords: maize; synthetics.

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* Part of a thesis submitted by the senior author in partial fulfillment of the M.S. degree.