Based on our primary database of the flower opening time (FOT) and flower exposure duration (FED) of 1114 rice (Oryza sativa ssp. indica) landraces, we examined the influences of growing season, sunrise time as well as day maximum and minimum temperatures on the anthesis behaviour of indica rice landraces of South and Southeast Asia, flowering in summer and winter in 3 consecutive years (2020–2022). We also compared the FOT and FED on sunny and cloudy days of a small set of landraces, and also during summer and winter. Our data show that rice florets tend to open later in the morning and lengthen the sunrise‐to‐anthesis duration (SAD) on hotter sunny days during tropical summer than during winter and on cloudy days. These findings contradict the widely held conjecture, based on studies conducted at colder latitudes, that rice flowers open earlier in the morning to avoid heat stress. We propose that indica rice landraces are sufficiently adapted to tropical summer because they were selected and bred over millennia to withstand heat stress during tropical summer, so their FOT and SAD are weakly influenced by high day temperatures. However, the significant reduction in FED of these landraces, whose flowers open later in mid‐day, seems to be an adaptive mechanism to avoid longer exposure to rising air temperature approaching day maximum temperature.

中文翻译：

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热带水稻（Oryza sativa ssp. indica）地方品种的花开放时间和持续时间响应热应激的调整

基于我们 1114 米的花开放时间 (FOT) 和花暴露持续时间 (FED) 的主要数据库 (水稻亚种。籼稻）地方品种，我们研究了生长季节、日出时间以及白天最高和最低温度对开花行为的影响籼稻南亚和东南亚的水稻地方品种，连续三年（2020-2022）在夏季和冬季开花。我们还比较了一小部分地方品种在晴天和阴天以及夏季和冬季的 FOT 和 FED。我们的数据显示，与冬季和阴天相比，在热带夏季炎热的晴天，稻花往往在早上较晚开放，并且日出到开花的持续时间（SAD）更长。这些发现与基于在较冷纬度地区进行的研究的广泛持有的猜想相矛盾，即稻花在早晨早些时候开放以避免热应激。我们建议籼稻水稻地方品种足以适应热带夏季，因为它们经过数千年的选择和培育，可以承受热带夏季的热应激，因此它们的 FOT 和 SAD 受白天高温的影响微弱。然而，这些地方品种的 FED 显着减少（其花在中午晚些时候开放）似乎是一种适应性机制，以避免长时间暴露在接近白天最高温度的上升气温中。