Abstract Breeding heavier seeds while maintaining seed number has been proposed as an effective strategy to improve oil crop production. Recent studies assessing rapeseed source-sink (S-Sratio) reduction after flowering suggest a window in the early seed-filling period that can compensate, either partially or totally, for a decrease in the number of seeds. However, little evidence has been reported in relation to the key window for seed plasticity in rapeseed. Furthermore, such studies have only assessed spring rapeseed genotypes and there is a lack of information on winter rapeseed. This study aims to elucidate the occurrence of a narrow window when seed plasticity is greatest, which is hypothesized to occur during the early stages of seed filling after the beginning of flowering in both winter and spring rapeseed genotypes. To asses this hypothesis, two winter and two spring rapeseed hybrids were evaluated under three S-Sratio treatments in two experiments performed in field conditions in Valdivia, Chile. The winter hybrids Trust and Mercedes were assessed under different nitrogen levels, and the spring hybrids Lumen and Solar were assessed using two sowing dates. S-Sratio treatments in both rapeseed genotypes consisted of a control without S-Sratio manipulation, a reduced S-Sratio from the beginning of flowering [BBCH 61] to 15 days after flowering (DAF) and a reduced S-Sratio from 15 to 30 DAF. The S-Sratio was reduced by shading the crop with black nets to intercept 75 % of the incoming solar radiation. Shading treatments decreased seed yield relative to the control between 13 and 42 % for the winter genotypes and from 23 to 44 % for the spring genotypes. The negative effect of shading on seed number under both S-S reduction timings explains the seed yield reduction. Interestingly, different windows of time for seed weight plasticity were found in response to the lower S-Sratio for winter and spring genotypes (i.e., 15–30 and 0–15 DAF, respectively). In the winter-type genotypes, seed weight increased between 28 and 33 % under the 15–30 DAF shading treatment, while seed weight in spring-type genotypes increased from 15 to 39 % during the 0–15 DAF treatment. Seed weight change was almost negligible outside of the sensitivity window as this trait increased only 2% at 0–15 DAF in winter-type genotypes and 7% at 15–30 DAF in spring-type genotypes, across treatments. In parallel, the S-S reduction decreased seed number by 23.6 and 40 %, at the 0–15 and 15–30 DAF treatment, respectively. The study showed statistical differences for seed oil and protein concentration across treatments, but both quality traits remained highly stable to the S-S reduction and showed similar behavior in winter and spring rapeseed types. Seed oil concentration changed little while seed protein concentration was more sensitive to seed weight response. The findings of the present study suggest that seeds per silique and seed weight are determined by the plant assimilate S-Sratio; therefore, seed number and seed weight determinations overlap as has been demonstrated in other crops like wheat, barley, sorghum and sunflower.

中文翻译：

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冬春油菜籽粒重可塑性在花后窄但不同的窗口内较高

摘要 在保持种子数量的同时培育较重的种子已被提出作为提高油料作物产量的有效策略。最近评估开花后油菜籽源库 (S-Sratio) 减少的研究表明，在早期种子灌浆期有一个窗口，可以部分或全部补偿种子数量的减少。然而，关于油菜籽种子可塑性的关键窗口的报道很少。此外，此类研究仅评估了春季油菜籽的基因型，缺乏有关冬季油菜籽的信息。本研究旨在阐明当种子可塑性最大时出现窄窗口，假设这发生在冬季和春季油菜基因型开花开始后种子灌浆的早期阶段。为了评估这一假设，在智利瓦尔迪维亚的田间条件下进行的两个实验中，在三种 S-Sratio 处理下对两个冬季和两个春季油菜籽杂交种进行了评估。冬季杂种 Trust 和 Mercedes 在不同的氮水平下进行评估，春季杂种 Lumen 和 Solar 使用两个播种日期进行评估。两种油菜籽基因型中的 S-Sratio 处理包括未进行 S-Sratio 操作的对照、从开花开始 [BBCH 61] 到开花后 15 天 (DAF) 降低 S-Sratio 以及从 15 到 30 降低 S-Sratio达夫。通过用黑网遮蔽作物以拦截 75% 的入射太阳辐射，从而降低了 S 比率。与对照相比，遮荫处理使冬季基因型的种子产量降低了 13% 至 42%，春季基因型降低了 23% 至 44%。在两种 SS 减少时间下阴影对种子数量的负面影响解释了种子产量的减少。有趣的是，在冬季和春季基因型（即分别为 15-30 和 0-15 DAF）的 S-Sratio 较低的情况下，发现了种子重量可塑性的不同时间窗口。在冬季型基因型中，在 15-30 DAF 遮荫处理下，种子重量增加了 28% 到 33%，而在 0-15 DAF 处理期间，春季型基因型的种子重量从 15% 增加到 39%。在敏感性窗口之外，种子重量变化几乎可以忽略不计，因为该性状在冬季型基因型的 0-15 DAF 时仅增加了 2%，在春季型基因型的 15-30 DAF 时，在整个处理中仅增加了 7%。同时，在 0-15 和 15-30 DAF 处理下，SS 减少分别使种子数减少了 23.6% 和 40%。该研究表明，不同处理的种子油和蛋白质浓度存在统计学差异，但两种品质性状对 SS 减少保持高度稳定，并在冬季和春季油菜籽类型中表现出相似的行为。种子油浓度变化不大，而种子蛋白质浓度对种子重量反应更敏感。本研究的结果表明，单角果种子数和种子重量由植物同化物 S-Sratio 决定；因此，正如在小麦、大麦、高粱和向日葵等其他作物中所证明的那样，种子数量和种子重量的确定是重叠的。种子油浓度变化不大，而种子蛋白质浓度对种子重量反应更敏感。本研究的结果表明，单角果种子数和种子重量由植物同化物 S-Sratio 决定；因此，正如在小麦、大麦、高粱和向日葵等其他作物中所证明的那样，种子数量和种子重量的确定是重叠的。种子油浓度变化不大，而种子蛋白质浓度对种子重量反应更敏感。本研究的结果表明，单角果种子数和种子重量由植物同化物 S-Sratio 决定；因此，正如在小麦、大麦、高粱和向日葵等其他作物中所证明的那样，种子数量和种子重量的确定是重叠的。