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Model Concepts to Express Genetic Differences in Maize Yield Components

Dep. of Crop and Soil Sci., Michigan State Univ., East Lansing, MI 48824-1325

* Corresponding author (ritchie{at}msu.edu)

Received for publication May 1, 2001. Maize (Zea mays L.) grain yield is closely related to kernel number per unit area. The quantification of genetic differences among maize cultivars to kernel number plant^-1 (KNP) is critical for accurate yield simulation but remains one of the less accurate components of yield modeling. Our objective was to document the recently published KNP data and revise CERES Maize model (V3.5). The duration of a critical window for KNP simulation was 327°C days (227°C days before and 100°C days after silking—base temperature 8°C) when ears actively grew. The KNP was curvilinearly related to cumulative intercepted photosynthetically active radiation plant^-1 (CIPAR) during the critical window. Potential kernel ear^-1 and kernel produced per unit CIPAR were the genetic coefficients needed to simulate KNP. Apical ears produced maximum KNP at a plateau CIPAR of 64 MJ, and prolific hybrids produced secondary ears when CIPAR exceeded 64 MJ. The genetic differences in prolificacy in low plant density were expressed by another coefficient. Below a threshold CIPAR of 11 MJ, all plants were barren, and a barrenness coefficient expressed genetic differences among old and modern hybrids to produce KNP in high plant density. Sensitivity analysis with limited testing indicated that the revised model simulated yield reasonably well [root mean square error (RMSE) = 0.63 Mg ha^-1] compared with the original model (RMSE = 1.25 Mg ha^-1) across a wide range of plant densities. However, rigorous testing of the model will be required to gain greater confidence in the proposed concepts.

Abbreviations: AIPAR, average intercepted photosynthetically active radiation plant^-1 day^-1 • CIPAR, cumulative intercepted photosynthetically active radiation plant^-1 • KN₁, kernel number of apical ear • KN₂, kernel number of the second ear • KNP, kernel number plant^-1 • PGR, plant growth rate • RMSE, root mean square error

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