Genetic improvement in maize (Zea mays L.) grain yield is associated with improvements in dry matter accumulation during the grain-filling period and the ability to maintain partitioning to the grain (i.e., harvest index) when grown at higher plant population densities. Although several attributes have been identified that lead to improved dry matter accumulation during the grain-filling period, the attributes that have enabled the maintenance of harvest index at higher plant population densities remain elusive. Using the Ontario ERA hybrids that represent five eras of genetic improvement in Ontario, we examined genetic improvement in several attributes associated with sink establishment and partitioning to the grain. We show that the number of florets on an ear initial is not influenced by plant density, nor is there any evidence of a genetic improvement in floret number. There has been genetic improvement, however, in the ability to support kernel set at a lower threshold level of dry matter accumulation and to more efficiently set kernels at lower dry matter accumulation levels, such as those experienced at higher plant densities. Genetic improvement is evident for reduced plant-to-plant variability for dry matter accumulation, grain yield, kernel number, and plant growth rate around silking, but most notably for grain yield. Finally, we show that genetic improvement in reduced plant-to-plant variability for grain yield is the result of the lower threshold dry matter levels required for seed set and the improved resource utilization, which has led to greater stability of individual plant performance in a stand.

中文翻译：

---

玉米库建立和植物间变异性遗传改良的生理机制

玉米遗传改良（Zea maysL.) 谷物产量与灌浆期干物质积累的改善以及在较高植物种群密度下种植时维持谷物分配的能力（即收获指数）有关。尽管已经确定了几种导致灌浆期干物质积累改善的属性，但在较高的植物种群密度下能够维持收获指数的属性仍然难以捉摸。使用代表安大略省遗传改良五个时代的安大略 ERA 杂交种，我们检查了与库建立和谷物分配相关的几个属性的遗传改良。我们表明，穗首上的小花数量不受植物密度的影响，也没有任何证据表明小花数量有遗传改善。然而，在支持以较低干物质积累阈值水平结粒和更有效地在较低干物质积累水平下结粒（例如在较高植物密度下经历的那些）的能力方面，存在遗传改良。遗传改良明显降低了植物间干物质积累、谷物产量、籽粒数和吐丝前后植物生长率的变异性，但最显着的是谷物产量。最后，我们表明，减少植物间谷物产量变异性的遗传改良是结实所需干物质阈值较低和资源利用率提高的结果，这导致单株植物性能在站立。能够在较低的干物质积累阈值水平上支持籽粒结实，以及更有效地在较低的干物质积累水平下结实籽粒，例如在较高植物密度下经历的那些。遗传改良明显降低了植物间干物质积累、谷物产量、籽粒数和吐丝前后植物生长率的变异性，但最显着的是谷物产量。最后，我们表明，减少植物间谷物产量变异性的遗传改良是结实所需干物质阈值较低和资源利用率提高的结果，这导致单株植物性能在站立。能够在较低的干物质积累阈值水平上支持籽粒结实，以及更有效地在较低的干物质积累水平下结实籽粒，例如在较高植物密度下经历的那些。遗传改良明显降低了植物间干物质积累、谷物产量、籽粒数和吐丝前后植物生长率的变异性，但最显着的是谷物产量。最后，我们表明，减少植物间谷物产量变异性的遗传改良是结实所需干物质阈值较低和资源利用率提高的结果，这导致单株植物性能在站立。遗传改良明显降低了植物间干物质积累、谷物产量、籽粒数和吐丝前后植物生长率的变异性，但最显着的是谷物产量。最后，我们表明，减少植物间谷物产量变异性的遗传改良是结实所需干物质阈值较低和资源利用率提高的结果，这导致单株植物性能在站立。遗传改良明显降低了植物间干物质积累、谷物产量、籽粒数和吐丝前后植物生长率的变异性，但最显着的是谷物产量。最后，我们表明，减少植物间谷物产量变异性的遗传改良是结实所需干物质阈值较低和资源利用率提高的结果，这导致单株植物性能在站立。