Source-sink balance in wheat under abiotic stress: Dissecting the spatio-temporal dynamics of grain filling

小麦是最重要的主粮作物之一，粮食高产对全球粮食安全至关重要。在之前的大量工作中，我们证实了小麦产量潜力的限制主要是由与源库关系有关的性状决定的：现代品种的生物量、养分利用效率、收获指数、光截获和辐射利用效率随着粒数的增加而增加。然而，它们仍然携带许多不利于源库性状的等位基因。在不同环境和管理情景下，我们对大量历史冬小麦品种进行了源库相关性状的广泛表型分析。这使我们能够鉴定出源强度增强的现代品种，这主要得益于高水分和氮吸收效率、高生物量潜力和/或高辐射拦截/利用效率，或者主要由高单位面积粒数赋予的显著汇强度。然而，这些假定的生理优势并不总是导致粮食产量的增加：相反，这些基因型往往在不规则的粮食形成、粮食发育的时空变异性或其他源库权衡方面表现出汇缺陷。本子项目是“小麦源库关系与限制（WheatSouSi）”一揽子提案中的子项目，目的是生成描述在不同环境约束下生长的遗传多样性冬小麦品种主茎和次分蘖轴行数相关的粒数和粒大小空间分布的详细数据，并将该信息与其他子项目收集的其他综合源库数据集进行比较。我们还将分析不同环境条件下茎秆可溶性碳水化合物、花粉活力、籽粒密度和籽粒重之间的关系。这些数据将用于评估在最佳和胁迫条件下与茎可溶性碳水化合物可用性相关的育性和繁殖力相关的关键基因的不同等位基因组合的利益和权衡。最后，我们将与合作子项目开展联合分析，研究不同发育时间点的非生物胁迫响应，将茎碳水化合物数据应用于源库模型，并评估由于育种而导致的与产量共选择相关的性状的等位基因转移。总的来说，这些综合的联合分析将为谷物产量的遗传增益对现代小麦源库关系的影响提供新的见解。

Wheat is one of the most important staple food crops and high grain yields are essential for global food security. In extensive previous work we confirmed that limitations to wheat yield potential are primarily determined by traits implicated in source-sink relations: Modern cultivars show increases in biomass, nutrient use efficiency, harvest index, light interception and radiation utilisation efficiency along with an elevated grain number. However, all still carry many detrimental alleles for source-sink traits.We performed extensive phenotyping of source- and sink-related traits under diverse environmental and management scenarios in a large panel of historical winter wheat cultivars. This enabled us to identify modern cultivars with enhanced source strength, facilitated by high water and nitrogen uptake efficiency, high biomass potential and/or high radiation interception/use efficiency, or with remarkable sink strength imparted mainly by a high number of grains per unit area. However, these putative physiological advantages did not always result in increased grain yield: Instead, such genotypes often showed sink deficits in terms of irregular grain formation, spatio-temporal variability for grain development, or other source-sink tradeoffs.The aim of this subproject in the Package Proposal “Wheat source-sink relationships and limitations (WheatSouSi)” is to generate detailed data describing the spatial distribution of grain number and grain size in relation to rachis row number on main stems and secondary tillers of genetically diverse winter wheat cultivars, grown under different environmental constraints, and compare this information with other comprehensive source-sink datasets collected in other subprojects. We will also analyze the relationships between stem soluble carbohydrates, pollen viability, grain set and grain weight, in a spatial context along the length of the spike, under different environmental constraints. This data will be used to evaluate benefits and trade-offs of different allelic combinations of key genes involved in fertility and fecundity in relation to the availability of stem soluble carbohydrates under optimal vs. stress conditions. Finally, we will perform joint analyses with cooperating subprojects to investigate abiotic stress responses at different developmental timeponts, to implement stem carbohydrate data into source-sink models, and to evaluate allelic shifts related to traits under co-selection with grain yield as a consequence of breeding. Collectively, these comprehensive joint analyses will give novel insight into the impact of genetic gain for grain yield on source-sink relationships in modern wheat.