Continuing to raise the potential yield of wheat through breeding is essential for global food security. Past progress has largely been associated with greater grains/m (GN), the critical period for the determination of which relates to spike growth, with GN often closely related to spike dry weight at anthesis (g/m). This focussed review outlines the importance of the critical period duration (Ds, in days or °Cdays) and questions how it may be increased genetically, relying partly on the long involvement of the authors in this field, primarily with lower latitude crops of spring-type wheat. Ds is further defined as the interval between flag leaf emergence and first anthesis, each across 50 % of the culms in any crop, a period encompassing most of the accumulation of spike dry matter, in turn determining floret survival and final fertile floret numbers/m. Natural temperature variation and temperature manipulation, particularly in field crops, confirm the dependence of Ds on temperature, which in °Cdays varies from about 300–500, depending on photoperiod. Evidence points to a stronger influence of night than day temperature on Ds, while maintaining the close positive Ds relationship to GN. However, genetic variation in the response of Ds to temperature appears very minor. Ds is inversely related to photoperiod, again with the expected effects on spike dry weight, fertile florets and GN. Extended photoperiod during the critical period showed the greatest reduction in GN per day advance in anthesis. Ds responses can be related to the major photoperiod sensitivity alleles present. A field experiment with a unique reduced photoperiod treatment demonstrated a strong positive effect on Ds, fertile florets and GN, especially in the fully recessive photoperiod-sensitive isoline. While more recent varieties tend to have a longer Ds, experiments targeting selection for Ds or closely related intervals have delivered little change in Ds, which often showed low heritability. Field photoperiod shortening studies needs further testing as proof of concept. Better selection studies are also needed. At the same time, knowledge of the molecular basis of the leaf response to photoperiod is such that gene editing is surely ripe to tackle the challenge of down-regulating this response only during the critical period, thereby increasing Ds and GN. Exogenous application of plant development regulators at the appropriate stage may also provide a way forward.

中文翻译：

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通过瞄准关键期持续时间来提高小麦作物每平方米粒数的育种：综述


通过育种继续提高小麦的潜在产量对于全球粮食安全至关重要。过去的进展很大程度上与更大的粒数/米 (GN) 有关，确定其关键时期与穗生长有关，GN 通常与花期穗干重 (g/m) 密切相关。这篇重点综述概述了关键期持续时间（Ds，以天或°C天为单位）的重要性，并质疑如何通过遗传手段增加关键期，部分依赖于作者在这一领域的长期参与，主要是低纬度春季作物。类型小麦。 Ds 进一步定义为剑叶出现和第一次开花之间的间隔，每个间隔跨越任何作物中 50% 的秆，这一时期涵盖了穗干物质的大部分积累，进而决定了小花的存活率和最终的可育小花数量/平方米。自然温度变化和温度控制，特别是在大田作物中，证实了 Ds 对温度的依赖性，在°Cdays 中，温度变化范围约为 300-500，具体取决于光周期。有证据表明夜间温度对 Ds 的影响比白天更强，同时 Ds 与 GN 保持密切的正相关关系。然而，Ds 对温度反应的遗传变异似乎非常小。 Ds 与光周期成反比，同样与对穗干重、可育小花和 GN 的预期影响有关。关键时期延长光周期显示花期提前每天 GN 的最大减少。 Ds 反应可能与存在的主要光周期敏感性等位基因有关。一项采用独特的缩短光周期处理的田间实验表明，对 Ds、可育小花和 GN 有很强的积极作用，特别是在完全隐性的光周期敏感等系植物中。 虽然较新的品种往往具有较长的 Ds，但针对 Ds 或密切相关区间选择的实验几乎没有带来 Ds 的变化，这通常表现出较低的遗传力。现场光周期缩短研究需要进一步测试作为概念证明。还需要更好的选择研究。与此同时，对叶子对光周期反应的分子基础的了解使得基因编辑肯定已经成熟，可以解决仅在关键时期下调这种反应的挑战，从而增加 Ds 和 GN。在适当的阶段外源应用植物发育调节剂也可能提供一条前进的道路。