Intra-specific competition affects the density tolerance and grain yield of maize hybrids

Increasing plant density usually increases the intra-specific competition of maize plants. This study was conducted to determine whether maize (Zea mays L.) hybrid density tolerance is related to intra-specific competition. Field experiments were conducted using a split-plot design, the main plots contained four maize hybrids, and subplots were 12 plant densities varied from 1.5 to 18 x 10(4) plants ha(-1). This study focused on dry matter accumulation, grain yield (GY), competition intensity (CI), and absolute severity of competition (ASC) based on the above treatments. Among all tested hybrids, GY exhibited a curvilinear response to plant density, which was well characterized by the Steinhart-Hart equation. Maize hybrids differed in optimum GY in descending order as follows: Zhongdan909 (ZD909) > Xianyu335 (XY335) = Yedan13 (YD13) > Zhongdan2 (ZD2). The CI and ASC of tested maize hybrids indicated that intra-specific competition increased with increasing plant density. In most cases, the CI and ASC of older maize hybrids were higher than those of modern maize hybrids when plant density exceeded 9.0 x 10(4) plants ha(-1). The results showed that the slope of the linear regression of ASC and plant density (i.e., the k-value) could be used to compare the intra-specific CI of maize hybrids, and there were significant negative correlations of k-value with optimum plant density and GY. Intra-specific competition is negatively correlated with the density tolerance of maize hybrids. This relationship may provide new insights for determining future maize breeding targets.