Increase of maize harvest index to improve water und nutrient use efficiency for a more sustainable crop production

许多农作物的收获指数（HI =粮食产量/地上总生物量）在过去几十年中有了很大的提高。然而，自引进杂交种以来，玉米的HI仅略有增加。与其他作物相反，玉米的生物量产量与粮食产量之间存在密切的正相关关系。然而，谷物玉米的营养生物量的生产需要大量的水和养分。因此，提高HI可以提高水分和养分的利用效率，从而实现更可持续的生产。今后，随着水资源变得稀缺，以及为了满足环境限制而必须减少肥料的施用，这将特别重要。提出了提高玉米HI的两种途径：提高结实率和减少营养枝生物量。为提高籽粒结实率，本文拟重点研究盐胁迫对籽粒发育的影响及生长素在籽粒发育中的作用。我们的研究小组是第一个在授粉后不久测量籽粒质膜H+- atp酶活性的小组。该酶是通过H+共转运将己糖从外质体吸收到发育中的籽粒中的关键驱动因素。因此，在应用项目中，玉米植株将在类似大田的条件下在大型容器中生长，并使用质膜H+- atp酶活性激发子（生长素，梭菌素）处理，以改善粒实。在第一年，必须确定最佳剂量，而在第二年，将测试额外的应用日期。在这两年，控制授粉后两天将进行一次中间收获，并测量穗轴顶端和基部的糖浓度和H+- atp酶活性参数。在最终收获（成熟）时，将分析产量参数并确定水分和养分利用效率。在第三年，将在体内测量发育中的籽粒的胞外体pH，因为它直接受到质膜H+- atp酶活性的影响。在第二种方法中，将测试营养芽生长减少对玉米HI和资源利用效率的影响。通过应用一种赤霉素生物合成抑制剂来测试是否有可能对营养芽和穗轴生长产生不同的影响，从而打破这两个参数之间的强相关性。为了测试品种与抑制剂的相互作用，多效唑的最佳剂量将在6个玉米品种中确定，多效唑已经显示出积极的效果。施用时间也将有所不同，以便找到最佳的生长阶段的处理。最终选择3个肥效和产量最好的品种，试验减肥对养分利用效率的影响。

The harvest index (HI = grain yield/total aboveground biomass) of many agricultural crops has been strongly increased during the last decades. However, the HI of maize has only marginally increased since the introduction of hybrids. In maize, opposite to other crops, a close positive correlation exists between biomass production and grain yield. However, the production of vegetative biomass in grain maize requires high amounts of water and nutrients. The increase of the HI may thus improve water and nutrient use efficiency, allowing a more sustainable production. In future, this will be particularly important as water resources become scarce, and as applications of fertilizers have to be reduced to meet environmental limits.We suggest two ways for improvement of maize HI: increase in kernel setting and decrease of vegetative shoot biomass. For better kernel setting, the proposed research focuses on the effect of salt stress and the role of auxins in grain development. Our research group was the first to measure plasma membrane H+-ATPase activity in kernels shortly after pollination. This enzyme is the key driver for hexose uptake from the apoplast into the developing kernels via H+ cotransport. Thus, in the applied project maize plants will be grown under field-like conditions in large containers and treated with elicitors of plasma membrane H+-ATPase activity (auxin, fusicoccin) to improve kernel setting. In the first year, the optimal dosage has to be determined, whereas in the second year additional application dates will be tested. In both years, two days after controlled pollination an intermediate harvest will be conducted and sugar concentrations and H+-ATPase activity parameters in apical and basal parts of the cob will be measured. At final harvest (maturity) yield parameters will be analyzed and water and nutrient use efficiencies determined. In the third year the apoplastic pH in the developing kernels will be measured in vivo, as it is directly affected by plasma membrane H+-ATPase activity.In a second approach the effect of reduced vegetative shoot growth on maize HI and resource use efficiencies will be tested. By application of a gibberellin biosynthesis inhibitor it will be tested whether it is possible to affect vegetative shoot and cob growth differently and thus break the strong correlation between both parameters. To test cultivar-inhibitor interactions, the optimal dosage of paclobutrazol, which has already shown positive effects, will be determined with six maize cultivars. Application time will be varied as well in order to find the optimum growth stage for the treatment. Eventually three cultivars, which performed best in HI and grain yield, will be chosen and the effect of reduced fertilizer amendment on nutrient use efficiencies will be tested.