ABSTRACT Cold tolerance of New Rice for Africa (NERICA) and their parent varieties was evaluated under natural air temperature conditions of Kenyan tropical highlands using the multiple-sown field evaluation method. Rice varieties were cultivated 10 times to expose them to a shift in temperature during 20-day periods before heading (critical period), measuring the average daily mean temperature during the critical period (Tmean) for each variety and filled grain ratio, which was used as an indicator of cold tolerance. Tmean of each variety was low in 6 out of 10 experiments. In the remaining four high-temperature experiments, there were no significant varietal differences in filled grain ratio. In the six low-temperature experiments, all varieties experienced 20.1−21.5°C Tmean. After comparison under virtually the same cold stress, NERICA 1, 3, 4, 7−10, 12, 17, 18, and WAB 56–104 were judged as cold-tolerant; NERICA 2, 5, 11, 13, and 14, and WAB 56–50 and 181–18 were moderately tolerant, and NERICA 6, 15, and 16 were cold-susceptible varieties. These evaluations generally corresponded with previous experimental results under temperature-controlled environments, showing the practicality of multiple-sown field cold tolerance evaluation in Kenya. It also indicated that NERICA varieties, which recorded different levels of cold tolerance and whose average number of days to heading in all experiments were 66−78, are suitable as a set of standard check varieties in this region to evaluate cold tolerance of rice varieties with this range of days to heading. Graphical Abstract

中文翻译：

---

肯尼亚热带高原自然低温条件下水稻生殖生长期耐寒性评价方法

摘要 采用多播田间评价方法，在肯尼亚热带高地自然气温条件下，对非洲新稻（NERICA）及其亲本品种的耐寒性进行了评价。水稻品种在抽穗前 20 天（关键期）期间栽培 10 次，使其暴露在温度变化中，测量每个品种关键期的平均日平均温度 (Tmean) 和饱满的籽粒率，使用作为耐寒指标。在 10 次实验中的 6 次中，每个品种的 T 均值较低。在剩余的四个高温试验中，填充粒比没有显着的品种差异。在六个低温实验中，所有品种都经历了 20.1-21.5°C Tmean。在几乎相同的冷应激下进行比较后，NERICA 1, 3, 4, 7-10、12、17、18 和 WAB 56-104 被判断为耐寒；NERICA 2, 5, 11, 13, 14和WAB 56-50和181-18为中度耐寒品种，NERICA 6, 15, 16为耐寒品种。这些评估通常与之前在温控环境下的实验结果一致，显示了肯尼亚多播田间耐寒性评估的实用性。表明耐寒性水平不同、平均抽穗天数为 66~78 天的 NERICA 品种适合作为本地区水稻品种耐寒性评价的标准对照品种。这个范围的天数。图形概要 WAB 56-50 和 181-18 为中度耐寒品种，NERICA 6、15 和 16 为耐寒品种。这些评估通常与之前在温控环境下的实验结果一致，显示了肯尼亚多播田间耐寒性评估的实用性。表明耐寒性水平不同、平均抽穗天数为 66~78 天的 NERICA 品种适合作为本地区水稻品种耐寒性评价的标准对照品种。这个范围的天数。图形概要 WAB 56-50 和 181-18 为中度耐寒品种，NERICA 6、15 和 16 为耐寒品种。这些评估通常与之前在温控环境下的实验结果一致，显示了肯尼亚多播田间耐寒性评估的实用性。表明耐寒性水平不同、平均抽穗天数为 66~78 天的 NERICA 品种适合作为本地区水稻品种耐寒性评价的标准对照品种。这个范围的天数。图形概要 展示了肯尼亚多播田间耐寒性评估的实用性。表明耐寒性水平不同、平均抽穗天数为 66~78 天的 NERICA 品种适合作为本地区水稻品种耐寒性评价的标准对照品种。这个范围的天数。图形概要 展示了肯尼亚多播田间耐寒性评估的实用性。表明耐寒性水平不同、平均抽穗天数为 66~78 天的 NERICA 品种适合作为本地区水稻品种耐寒性评价的标准对照品种。这个范围的天数。图形概要