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，预计气温将升高，植物供水量将减少，这很可能导致作物产量下降。这两种应力条件同时发生在现场，在不久的将来，联合应力的发生率将增加。然而，人们对它们对植物的综合影响知之甚少。小麦是一种热敏性较强的作物，其产量潜力由单株或单位面积成穗数、穗粒数和单粒重三个参数决定。这些产量决定因素在特定的生长阶段受到影响：分蘖，茎伸长，开花和灌浆。因此，需要研究小麦发育的各个阶段，以确定在胁迫条件下籽粒产量表现的决定性因素。到目前为止，大多数研究集中在灌浆期，而在营养生长和开花期的单独和特别是组合的热和干旱胁迫的影响的调查是罕见的。胁迫条件下小麦籽粒产量的下降可能是由于同化物的有效性受到限制（源限制），也可能是由于库强度降低。我们在前期的研究中发现，在持续高温胁迫下，小麦植株能够显著增加成穗分蘖数。这种产量稳定的潜力只能部分地被利用，因为籽粒结实强烈减少，但所建立的籽粒表现出良好的灌浆。没有观察到源限制，但库容量减少（更少和更小的内核），可能也汇活动。这一点值得进一步研究的酶，特别是酸性转化酶，质膜H+-ATP酶，淀粉合成酶。在拟议的项目中，单独或组合的热和干旱胁迫将施加到两个小麦品种在营养生长，开花期，或在籽粒灌浆。此外，将测试营养生长期间干旱引发对开花期间受胁迫的植物的谷物产量表现的影响，并评估小麦植物从胁迫中恢复的能力。将研究确定源或库强度的各种参数，无论是在生长中的植物的测量，还是在灌浆期间或生理成熟期收获的不同植物器官的分析。本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，什么是谷物产量发展的限制因素。这些知识将有助于鉴定决定耐热性和/或抗旱性的性状，并可用于育种计划，以提高胁迫下的产量稳定性。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.