Ear and Kernel Formation in Maize Hybrids Representing Three Decades of Grain Yield Improvement in Ontario

Increased prolificacy and reduced barrenness have been identified as physiological traits in maize (Zea mays L.) hybrids that are tolerant of environmental stresses induced by high plant density. The objective of this study was to investigate ear and kernel formation under a range of plant densities in old and new hybrids. Experiments were carried out during 1987 and 1988 at two locations in Ontario with nine maize hybrids representing three decades of yield improvement in Ontario, grown at 2, 4, 8, 10, and 13 plants m⁻². Dry matter was measured at 1 wk presiiking, 3 wk postsilking, and at physiological maturity and plant growth rates calculated for both periods. Grain yield, kernel weight, and kernel number were determined at physiological maturity. Kernels per plant and plant growth rate for the period from 1 wk presilking to 3 wk postsilking could be fitted to a discontinuous function of multiple rectangular hyperbolae; a single rectangular hyperbola was associated with the kernel number on each grain-bearing ear. The first rectangular hyperbola for each hybrid had a positive x-axis intercept, which was interpreted as the threshold plant growth rate for ear formation. The analysis showed that grain yield improvement of Ontario maize hybrids was associated with an increase in kernel number per plant and higher plant growth rates from 1 wk presilking to 3 wk postsiiking. The increase in kernels per plant was associated with an increase in ears per plant. The increased prolificacy of recent hybrids appeared to be the combined result of higher rates of plant dry matter accumulation during silking and a greater inherent tendency to exhibit prolificacy. The lower barrenness of recent hybrids at high plant densities was associated with higher plant growth rates, but was not the result of a lower threshold plant growth rate for ear formation. Joint contribution of Dep. of Crop Science, Univ. of Guelph and Agriculture Canada. LRRC Contribution no. 91-26. Research supported by Ontario Ministry of Agric. and Food, Agric. Canada and Natl. Science and Engineering Res. Council of Canada.