Flower opening time (FOT) is affected by genetic and environmental factors, but little is known about the effect of light and dark conditions on FOT in cereal crops. FOT of an indica rice cultivar, IR64, and its near-isogenic line carrying a QTL for an early-morning flowering trait (IR64+qEMF3) were investigated in a natural-light and temperature-controlled small greenhouse by exposing either the panicle or stem or both plant organs to different light and dark conditions. FOT did not change in either genotype when panicles were exposed to light. A large difference in FOT was found between genotypes when panicles were exposed to dark conditions; no flower opening was observed in IR64, whereas flower opening was delayed but observed in IR64+qEMF3. These results suggest that the panicle is the organ that perceives light for flower opening in both genotypes, whereas the light requirement to reach flower opening was quite different between genotypes. Flower opening of IR64 occurred concomitantly with elongation of anther filament in the light after the dark treatment stopped, whereas approximately half of flowering of IR64+qEMF3 resulted in apparent cleistogamy even during dark treatment. An extended duration of the dark treatment until 1730H (30–50 min before sunset) made FOT of IR64 spikelets on the next day shifted to a time as early as that of IR64+qEMF3, with significant advancement of FOT compared to the control IR64 spikelets. Our results indicated that different flowering responses to light and dark conditions exist between IR64 and IR64+qEMF3. These findings provide clues for understanding the unique genetic controls of flowering in an EMF line in rice. This study also showed evidence that artificial light environments can shift the FOT of IR64 to that of IR64+qEMF3.

中文翻译：

---

光照和黑暗条件对栽培稻（Oryza sativa）和近等基因早花系开花时间的影响

花开放时间（FOT）受遗传和环境因素的影响，但关于光照和黑暗条件对谷类作物FOT的影响知之甚少。在自然光和温度控制的小温室中，通过暴露穗或茎，研究了籼稻品种 IR64 及其携带早花性状 QTL (IR64+qEMF3) 的近等基因系的 FOT或两种植物器官适应不同的光照和黑暗条件。当圆锥花序暴露在光线下时，两种基因型的 FOT 均未发生变化。当圆锥花序暴露在黑暗条件下时，基因型之间的 FOT 存在很大差异；在 IR64 中未观察到开花，而在 IR64+qEMF3 中观察到开花延迟但观察到。这些结果表明，在两种基因型中，圆锥花序是感知开花的光的器官，而达到开花的光需求在基因型之间是完全不同的。在黑暗处理停止后，IR64 的开花伴随着花药丝在光照下的伸长，而 IR64+qEMF3 大约一半的开花导致即使在黑暗处理期间也出现明显的闭锁。黑暗处理持续时间延长至 1730H（日落前 30-50 分钟）使第二天 IR64 小穗的 FOT 转变为早于 IR64+qEMF3 的时间，与对照 IR64 小穗相比，FOT 显着提高. 我们的结果表明，IR64 和 IR64+qEMF3 之间存在对光照和黑暗条件的不同开花反应。这些发现为理解水稻 EMF 系开花的独特遗传控制提供了线索。该研究还表明，人造光环境可以将 IR64 的 FOT 转变为 IR64+qEMF3 的 FOT。