Plant Density Effects on Grain Yield per Plant in Maize: Breeding Implications

Breeding in maize (Zea mays L.) succeeded in improving tolerance to stresses and responsiveness to inputs, but failed to improve the potential yield per plant. Modern hybrids are highly productive, but their yield per unit area is dependent on high plant densities. Results of present study verified that modern hybrids require a narrow range of densities to give their maximum yield per unit area, since plant density affected significantly all kind of genetic materials. Results also showed that high densities are associated with high plant-to-plant variability and barrenness, affecting negatively the stability of hybrid performance. F2 and F1+F2 (mixture) genetic materials showed increasing yields, as plant density was increasing. This was due to high competition and the presence of heterotic plants. These findings pointed out the necessity for the development of maize hybrids with more stable performance across growing seasons. Density-independent hybrids can be effectively attained through selection in the absence of competition, aiming to improve the potential yield per plant. Very low densities, so that any plant-to-plant interference for growth resources use is eliminated, maximize mean yield per plant differentiation and optimise the phenotypic-genotypic correspondence, facilitating the identification of the superior entries. Evaluation under high plant densities may distinguish between different genetic materials, based on F2 yielding performance, to be used as starting materials in breeding programs. Even though the main goal is breeding for density-independent maize hybrids, since modern maize hybrids depend their yielding performance on higher plant densities, breeding for density tolerance may easily contribute to higher field yields.