Grain yield of wheat as affected by individual and combined heat and drought stress during different growth stages with emphasis on source/sink relations

在世界许多地区，预计气温会升高，植物的供水会减少，这很可能导致作物生产率下降。这两种应力条件在现场同时发生，在不久的将来，复合应力的发生率将会增加。然而，人们对它们对植物的联合影响知之甚少。小麦是一种对热相当敏感的作物，其产量潜力由三个参数决定：每株或每面积的结穗秆数、每穗粒数和单粒重。这些产量决定因素在特定的生长阶段受到特别的影响：分蘖、茎伸长、开花和灌浆。因此，需要研究小麦发育的不同阶段，以确定在胁迫条件下决定籽粒产量表现的决定因素。到目前为止，大多数研究都集中在籽粒灌浆期，而对营养生长和开花期的单独、特别是高温和干旱联合胁迫效应的研究很少。胁迫条件造成的小麦籽粒产量下降可能是由于同化物的可获得性受到限制(来源受限)，也可能是由于库容量降低。在我们之前的研究中，我们发现在持续的热胁迫下，小麦植株能够显著增加成穗分蘖的数量。这种稳产潜力只能部分利用，因为籽粒结实率大大降低，但已形成的籽粒表现出良好的灌浆效果。没有观察到来源限制，但库容量减少(籽粒更少、更小)，可能还会有库活性。这值得进一步研究涉及的酶，特别是酸性转化酶、质膜H+-ATPase和淀粉合成酶。在拟议的项目中，将在营养生长期、开花期或灌浆期对两个小麦品种施加单独或联合的高温和干旱胁迫。此外，还将测试营养生长期干旱引发对开花期逆境植株产量表现的影响，并评估小麦植株从逆境中恢复的能力。将通过对生长植株的测量或对籽粒灌浆或生理成熟期收获的不同植物器官的分析，研究决定源或库强度的各种参数。这项研究解决了一个重要的问题：当植物在不同的生长阶段容易受到不同的胁迫时，什么是影响粮食产量发展的石灰因素。这些知识将有助于鉴定决定耐热性和/或抗旱性的性状，并可纳入在胁迫下获得更高产量稳定性的育种计划。可以提高水分和养分的利用效率，以保护有限的资源，有利于更可持续的小麦生产。

In many world regions, higher temperatures and reduced water supply to plants are expected, most likely causing depressions in crop productivity. Both stress conditions occur in the field simultaneously, and incidences of combined stress will increase in the near future. However, relatively little is known about their combined impacts on plants. The grain yield potential of wheat, a rather heat-sensitive crop, is determined by three parameters: number of ear-bearing culms per plant or per area, kernel number per ear, and individual grain weight. These yield determinants are specifically affected at defined growth stages: tillering, stem elongation, flowering, and grain filling. Thus, various phases of wheat development need to be investigated in order to identify the decisive determinants for grain yield performance under stress conditions. So far, most studies focused on the grain-filling period, whereas investigations on individual and particularly combined heat and drought stress effects during vegetative growth and at anthesis are rare. Depressions in wheat grain yield caused by stress conditions can either be due to restricted availability of assimilates (source limitation), or by reduced sink strength. In our previous study, we found that under continuous heat stress wheat plants were able to strongly increase the number of ear-bearing tillers. This potential for yield stabilization could only partly be exploited as kernel setting was strongly reduced, yet the established kernels showed good grain filling. No source limitation was observed, but sink capacity was reduced (fewer and smaller kernels), and probably also sink activity. This merits further studies of the enzymes involved, particularly of acid invertase, plasma membrane H+-ATPase, and starch synthase. In the proposed project, individual or combined heat and drought stress will be applied to two wheat cultivars either during vegetative growth, at anthesis, or during grain-filling. In addition, the effects of drought priming during vegetative growth on grain yield performance of plants stressed during anthesis will be tested, and the ability of the wheat plants to recover from stress is evaluated. Various parameters which determine source or sink strength will be investigated, either with measurements at the growing plants or with analyses of different plant organs derived from harvests during grain filling or at physiological maturity. This study addresses the important question: What is the liming factor for grain yield development when plants are prone to the various stresses during different growth stages. This knowledge will contribute to the identification of traits which determine heat and/or drought resistance, and can be incorporated in breeding programs for higher yield stability under stress. The water- and nutrient-use efficiencies can be improved in order to protect limited resources and favor a more sustainable wheat production.