High yield, good eating quality, and high nitrogen (N) use efficiency present challenges in cultivating medium hybrid rice. We hypothesized that balanced source-sink relationships are key traits for achieving high yield, good eating quality, and high N use efficiency in medium hybrid rice under suitable N management regimes. Three field experiments were conducted with two medium hybrid rice cultivars. Five distinct N application levels, designated as N0, N75, N150, N225, and N300, were used to investigate varying source-sink characteristics and their impact on yield, eating quality, and N use efficiency. The results indicated that the ratio of dry matter at the heading stage to the number of spikelets per unit area (DM/Spik. R) exhibited a significant decrease with increasing N application rates in both cultivars over three years, except for the cultivar HLY898 in 2021. Conversely, an increase in N application rates generally increased the ratios of accumulated N rate and leaf area at the heading stage to the number of spikelets per unit area (AN/Spik. R and LA/Spik. R) across the cultivars and experimental years. Only AN/Spik. R showed significant relationships with yield, eating score, and N partial factor productivity (PFPN). In addition, significant differences were observed among the three study years for DM/Spik. R and LA/Spik. R, but no significant difference was found for AN/Spik. R across the three study years. Moreover, both N concentration and nitrogen nutrition index (NNI) at heading had significant and linear relationships with AN/Spik. R. Further analysis revealed that the highest yield and maximum eating scores, constituting 92 % of the total, were achieved when AN/Spik. R reached 3.65 mg per spikelet. Correspondingly, the NNI was recommended as 0.93 at heading when 90 % of the highest yield and maximum eating scores were harvested. Additionally, 79 % of the highest yield and maximum PFPN were obtained when AN/Spik. R and NNI were approximate to 2.58 mg per spikelet and 0.78 at heading, respectively. These results suggest that moderate AN/Spik. R corresponding to mild N deficiency at heading could be a key source-sink indicator for the integrated regulation of high yield, good eating quality, and high N use efficiency in medium hybrid rice.

中文翻译：

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中型杂交籼稻产量高、食味好、氮肥利用效率高——基于抽穗期源库平衡关系的视角


高产量、良好食味和高氮利用效率对中型杂交稻的培育提出了挑战。我们假设平衡的源库关系是在合适的氮肥管理制度下中型杂交稻实现高产量、良好食味和高氮肥利用效率的关键性状。使用两个中等杂交水稻品种进行了三个田间试验。五个不同的施氮水平（指定为 N0、N75、N150、N225 和 N300）用于研究不同的源库特征及其对产量、食用质量和氮利用效率的影响。结果表明，三年来，除HLY898品种外，两个品种抽穗期干物质与单位面积小穗数的比值（DM/Spik.R）均随施氮量的增加而显着下降。 2021. 相反，施氮量的增加通常会增加各品种的累积施氮量和抽穗期叶面积与单位面积小穗数的比率（AN/Spik.R 和 LA/Spik.R）。实验年。只有 AN/Spik。 R 与产量、进食评分和氮偏要素生产率 (PFP​​N) 显着相关。此外，在 DM/Spik 的三个研究年中观察到显着差异。 R 和 LA/Spik。 R，但 AN/Spik 没有发现显着差异。 R贯穿三个学习年。此外，抽穗期氮浓度和氮营养指数（NNI）均与AN/Spik呈显着线性关系。 R.进一步分析表明，AN/Spik 时获得了最高产量和最大进食分数，占总数的 92%。每个小穗的 R 达到 3.65 毫克。相应地，NNI推荐为0。抽穗期 93，此时收获了 90% 的最高产量和最大吃食分数。此外，当 AN/Spik 时，获得了 79% 的最高产率和最大 PFPN。 R 和 NNI 分别约为每小穗 2.58 毫克和抽穗时 0.78 毫克。这些结果表明 AN/Spik 是中等的。抽穗期轻度缺氮对应的R可能是综合调控中型杂交稻高产、食性好、氮素利用效率高的关键源库指标。