ABSTRACT Differentiate mechanism of wheat species in response to contrasting drought stress gradients implies a cue of its long-term domestication. In the present study, three water regimes including well-watered control (WW, 80% field water capacity (FC)), moderate drought stress (MS, 50% FC,) and severe drought stress (SS, 30% FC) were designed to reveal different responses of eight wheat species (four tetraploid and four hexaploid) representing different breeding decades and genetic origins to drought stresses. The data indicated that 50% FC and 30% FC fell into the soil moisture threshold range of non-hydraulic and hydraulic root signal occurrence, respectively. In general, grain yield, grain number/spike weight per plant, aboveground biomass, harvest index (HI) and water use efficiency (WUE) were significantly higher in hexaploid species than those of tetraploid species under drought stress (P < .05). Particularly, non-hydraulic root signal was triggered and continuously operated under 50% FC, while hydraulic root signal was observed under 30% FC, respectively. Under 80% FC, the allometric exponent (ɑ) of Maboveground vs Mroot decreased from tetraploid to hexaploid (both were of <1), indicating that during the domestication, the hexaploid species allocated less biomass to root system. For the relationship of Mear vs Mvegetative, the ɑ value was significantly greater in the hexaploid species, showing that hexaploid wheat distributed more biomass to ear than tetraploid to improve yield. Under 50% FC, this trend was enhanced. However, under 30% FC, there was no significant difference in the ɑ value between two species. Additionally, correlation analyses on yield formation affirmed the above results. Therefore, drought tolerance tended to be enhanced in hexaploid species under the pressure of artificial selection than that of tetraploid species. When drought stress exceeded a certain threshold, both species would be negatively seriously affected and followed a similar mechanism for better survival.

中文翻译：

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四倍体和六倍体小麦（Triticum aestivum L.）对中度和重度干旱胁迫的不同反应：小麦驯化的线索

摘要 小麦物种响应对比干旱胁迫梯度的分化机制暗示了其长期驯化的线索。在本研究中，设计了三种水分状况，包括充足浇水控制（WW，80% 田间持水量（FC））、中度干旱胁迫（MS，50% FC）和严重干旱胁迫（SS，30% FC）揭示代表不同育种年代和遗传起源的八种小麦（四种四倍体和四种六倍体）对干旱胁迫的不同反应。数据表明，50% FC 和 30% FC 分别落入非水力和水力根信号发生的土壤水分阈值范围。一般来说，谷物产量、每株植物的谷物数/穗重、地上生物量、在干旱胁迫下，六倍体物种的收获指数（HI）和水分利用效率（WUE）显着高于四倍体物种（P < .05）。特别是，在 50% FC 下触发和连续运行非液压根信号，而在 30% FC 下观察到液压根信号。在 80% FC 下，Maboveground 与 Mroot 的异速生长指数 (ɑ) 从四倍体减少到六倍体（均 <1），表明在驯化过程中，六倍体物种分配给根系的生物量较少。对于 Mear 与 Mvegetative 的关系，六倍体物种的 ɑ 值显着更大，表明六倍体小麦比四倍体小麦分配更多的生物量以提高产量。在 50% FC 下，这种趋势得到加强。然而，在 30% FC 以下，两个物种之间的ɑ值没有显着差异。此外，收益率形成的相关性分析证实了上述结果。因此，在人工选择的压力下，六倍体物种的耐旱性比四倍体物种有增强的趋势。当干旱胁迫超过某个阈值时，这两个物种都会受到严重的负面影响，并遵循类似的机制以获得更好的生存。