INTRODUCTION

The domestication of plants and animals was one of the most significant changes in human history. A managed cultivation of crops allowed a sedentary lifestyle and the division of work, which freed capacities to develop modern societies.

The change from a wild plant to a crop required substantial morphological and physiological adaptation. Crops with similar uses display similar trait changes, which are summarized in the domestication syndrome (Hammer, 1984). For grain crops, loss of seed shattering, increased seed size, and loss of seed dormancy are major domestication traits (Fig. 1). Crops that combine most domestication traits and consequently are well adapted to agroecological environments can be considered fully domesticated, while those that only display a few crop traits may be considered as incompletely domesticated. Although hundreds of grain crops have been cultivated by humans for millennia, most plants show only few of the domestication traits rather than the full syndrome (Meyer et al., 2012). Consequently, only a small fraction of the over 2000 crops that we know today are fully domesticated. Even crops that were of high importance for early cultures display only a minor fraction of the domestication syndrome. Studying the signals of incomplete crop domestication in minor crops could reveal the limits and constraints of crop selection and unlock the potential of novel crops for sustainable food production.

Here, I review the evidence of potential genetic limits and constraints that altered the path of crop domestication. I present potential genetic features that might have favored the rapid full domestication of certain plant species and hindered the complete domestication of others. My examples and conclusions are mostly based on annual grain crops because their domestication syndrome is well defined and overlapping. Yet, most of the concepts also hold true for tuber, root, fruit, and vegetable crops, although more domestication traits are based on human preferences (i.e., flavor and color) for these crops.

Evidence for incomplete domestication

Fully domesticated grain crops include maize, rice, and common bean, but hundreds of other crops, such as buckwheat, teff, and amaranth that have many favorable nutritional properties and are, or historically were, of high importance in their centers of domestication (Meyer et al., 2012) combine only a few domestication traits (Abrouk et al., 2020; Stetter et al., 2020). The loss of seed shattering, which is arguably one of the most important domestication traits for grain crops is lacking in many minor crops (Hammer, 1984). A lack of selection during early domestication is insufficient to explain incomplete trait adaptation because archaeological and genetic evidence suggest that minor crops have received equal selection pressure as fully domesticated crops. As a consequence of incomplete domestication, the production of these crops has strongly declined over the last centuries, as they were replaced by major crops that are fitter in agronomic settings. Today, many crops that are not fully domesticated are referred to as orphan crops because of their declined importance.

中文翻译：

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作物驯化的局限性和制约因素

介绍

动植物的驯化是人类历史上最重大的变化之一。进行有管理的农作物种植可以使人们久坐不动，使工作分工，从而解放了发展现代社会的能力。

从野生植物到农作物的转变需要充分的形态和生理适应性。具有相似用途的农作物表现出相似的性状变化，归纳在驯化综合症中（Hammer，1984）。对于谷物而言，种子破碎的损失，种子大小的增加以及种子休眠的丧失是主要的驯化性状（图1）。结合了大多数驯化性状并因此很好地适应农业生态环境的农作物可被视为完全驯化，而仅表现出几种作物性状的农作物可被视为未完全驯化。尽管人类已经种植了数百种谷物作物已有数千年的历史，但大多数植物仅表现出很少的驯化性状，而不是完全的综合症（Meyer等人，2012年））。因此，在我们今天知道的2000多种农作物中，只有一小部分是完全驯化的。即使是对早期栽培极为重要的农作物，也只显示出驯化综合症的一小部分。研究次要农作物不完全驯化的信号可能揭示出农作物选择的局限性和制约因素，并释放出新型农作物用于可持续粮食生产的潜力。

在这里，我回顾了潜在的遗传限制和制约因素改变了作物驯化途径的证据。我介绍了潜在的遗传特征，这些特征可能有利于某些植物物种的快速完全驯化，而阻碍了其他植物的完全驯化。我的例子和结论主要基于一年生粮食作物，因为它们的驯化综合症定义明确且重叠。然而，大多数概念对于块茎，块根，水果和蔬菜作物也适用，尽管更多的驯化特性是基于人类对这些作物的喜好（即风味和颜色）。

不完全驯化的证据

完全驯化的谷类作物包括玉米，水稻和普通豆，但是数百种其他作物，例如荞麦，塔夫和a菜，具有许多良好的营养特性，或者在历史上在其驯化中心都非常重要（Meyer等人，2012）仅结合了一些驯化性状（Abrouk等人，2020； Stetter等人，2020）。许多次要作物都缺乏种子破碎的损失，这可能是谷物作物最重要的驯化性状之一（Hammer，1984年）。）。早期驯化过程中缺乏选择不足以解释不完全的性状适应，因为考古和遗传证据表明，次要作物与完全驯化的作物承受相同的选择压力。由于驯化不完全，这些农作物的产量在过去的几个世纪中急剧下降，因为它们被适合农艺环境的主要农作物替代。今天，由于重要性下降，许多尚未完全驯化的农作物被称为孤儿作物。