The impact of plant population density on crop yield and response to selection in maize.

摘要

Plant population density represents the agronomic management factor in maize (Zea mays L.) that has changed considerably during the past six decades. The objective of this paper is to compare and interpret selection data from different eras in maize to answer the following questions: (1) how stand uniformity relates to yield per unit area, (2) how competition and density affect response to selection, and (3) is the development of density-independent hybrids in maize feasible. Two old double cross hybrids (DeKalb 29 and Pride 5) and two newer single cross hybrids (Pioneer 3851 and Pioneer 3902) were utilized across two years and eight different plant densities. The data demonstrated that plant population density affects crop yield and response to selection. Plant density affects crop yield indirectly, through the increase in the level of competition. Competition, i.e., the plant-to-plant interference with the equal sharing of growth resources increases almost linearly with the increase of plant density. Competition is measured by the coefficient of variation (CV) of single-plant yields. To maximize crop yield, it is essential to optimize stand uniformity by minimizing the plant-to-plant variation, i.e., by minimizing competition. In addition, high plant density was found to reduce response to selection because (1) it increases the CV of single-plant yields, (2) it reduces the single plant yield differences among the maize hybrids, and (3) it reduces the grain yield per plant. The grain yield per plant at high plant densities is reduced so significantly that it limits multi-site progeny testing in conventional trials in the early generations. Furthermore, the data demonstrate that high plant densities establish an unfavorable negative correlation between the mean yield of progeny plants and their CV, whereas under low plant densities these two parameters are not correlated. Future breeding priorities in maize should include single-plant selection over the target area of adaptation based on the three genetic components of crop yield measured accurately at ultra-low plant densities, i.e., yield potential per plant measured by the progeny mean, tolerance to stresses measured by the progeny standardized mean, and the ability to exploit added inputs measured by the standardized selection differential. This strategy could lead to the development of density-independent hybrids that yield optimally over a wide range of plant densities and ensure a number of advantages compared to density-dependent hybrids, especially when genetically modified Roundup Ready hybrids are considered.