The development of double-season rice cropping is advantageous for maximizing the utilization of radiation and temperature resources in rice production, while ensuring food security. However, late sowing often renders the late-season rice susceptible to cold stress during heading and flowering, leading to a low grain-setting rate and significant yield loss in subtropical zones. Despite this, the precise mechanisms through which low temperatures impact grain setting, along with the sensitivities of heading, flowering and pollination to cold stress, remain unclear across different types of rice. In this study, a field experiment involving multiple sowing dates and a pot experiment simulating low-temperature conditions during the booting and heading stages were conducted, using various late-season rice cultivars as materials. The heading degree, glume openness, anther dehiscence and pollen fertility were measured to determine their responses to ambient temperature. The results showed that late sowing significantly delayed the heading time of rice, exposing the plants to low temperatures during their heading and flowering in autumn. Under late sowing or simulated low-temperature conditions, the heading degree, anther dehiscence coefficient, and fertile pollen rate significantly decreased, resulting in lower grain-setting rates and grain yield across all rice types. However, glume opening remained unaffected in this study. The critical lowest daily temperatures for safe heading were identified as 18.5°C, 19.3°C and 22°C, and for safe anther dehiscence at heading, they were 19.9°C, 20°C and 22.3°C for japonica, indica-japonica hybrid and indica rice, respectively. Furthermore, the critical lowest daily temperatures for safe pollen fertility averaged 19.1°C, 20.2°C and 21.7°C in the 4–7 days prior to full heading for japonica, indica-japonica hybrid and indica rice, respectively. The cold tolerance in anther dehiscence of indica-japonica hybrid rice was similar to that of japonica rice but higher than that of indica rice, while the cold tolerance in heading and pollen fertility of indica-japonica hybrid rice was intermediate between japonica and indica rice. Path analysis revealed that low temperature decreased the grain-setting rate primarily by reducing anther dehiscence coefficient across all types of rice. Lower pollen fertility was another significant pathway through which low temperature decreased the grain-setting rate in indica rice. Planting japonica rice is recommended for the safe production of late-season rice in subtropical zones.

中文翻译：

---

低温对不同类型晚稻抽穗坐果率影响的鉴定


发展双季稻种植有利于在保证粮食安全的同时，最大限度地利用水稻生产中的辐射和温度资源。然而，晚播往往使晚季稻在抽穗和开花期间容易受到寒冷胁迫的影响，导致亚热带地区的坐果率低和产量损失严重。尽管如此，低温影响籽粒坐果的确切机制，以及抽穗、开花和授粉对寒冷胁迫的敏感性，在不同类型的水稻中仍不清楚。本研究以各种晚稻品种为材料，进行了涉及多个播种日期的田间试验和模拟孕穗和抽穗期低温条件的盆栽试验。测定抽穗度、花颖开放度、花药裂开度和花粉生育力，以确定它们对环境温度的响应。结果表明，晚播显著延迟了水稻的抽穗时间，使植株在秋季抽穗和开花期间暴露在低温下。在晚播或模拟低温条件下，所有水稻类型的抽穗度、花药裂开系数和受孕花粉率均显著降低，导致坐籽率和产量降低。然而，在本研究中，颖子开放不受影响。安全抽穗的临界日最低气温分别为 18.5°C、19.3°C 和 22°C，粳、籼粳杂交种和籼稻的安全花药开裂分别为 19.9°C、20°C 和 22.3°C。此外，安全花粉生育的关键最低日温度平均为 19.1°C、20.2°C 和 21°C。粳稻、籼粳杂交种和籼稻在抽穗前 4-7 天分别达到 7°C。籼粳杂交稻花药开裂的耐寒性与粳稻相似，但高于籼稻，而籼粳杂交稻的抽穗耐寒性和花粉肥力介于粳稻和籼稻之间。路径分析表明，低温主要通过降低所有类型水稻的花药裂开系数来降低坐粒率。较低的花粉肥力是低温降低籼稻坐粒率的另一个重要途径。建议种植粳稻，以便在亚热带地区安全生产晚季稻。