The major challenge for the rice–ratoon-rice system in cool-temperate environments is to ensure high ratooning ability from stubbles after harvesting of main rice crops. The choice of locally adapted cultivars with high ratooning ability is crucial for this system. We aimed at identifying modern ultrashort-duration cultivars with high ratoon rice yield in central Japan (35°N to 36°N), which represents the northern limit for growing a ratoon crop, and to elucidate the associated growth characteristics. We evaluated 15 ultrashort-duration cultivars (13 and 2 ) in 2019, 8 (7 and 1 ) in 2020, and 3 (all ) in 2021 in the rice–ratoon-rice system in Tokyo, Japan. Ratoon rice yield was not negatively correlated with the main rice yield in any year. However, the tiller regeneration rate (the ratio of tiller number in the ratoon rice season to the panicle number in the main rice season) was strongly and significantly positively correlated with ratoon rice yield. The cultivars (‘TNAU6484’ and ‘ADT30’) had lower tiller regeneration rates and lower ratoon rice yield than the cultivars. Two cultivars (‘Akitakomachi’ and ‘Ichibanboshi’) had the highest tiller regeneration rate and the highest ratoon rice yield. The stem nonstructural carbohydrate concentration was positively correlated with ratoon bud length at the harvest of the main rice crop. We found significant differences among cultivars in their ratooning ability. The nonstructural carbohydrates accumulated in stems at the harvest of the main rice crop might contribute to quicker and greater growth of ratoon rice crops in central Japan. Despite competition between stems and grains for photosynthate, this growth characteristic does not necessarily lower the yield of the main rice crop in ultrashort-duration cultivars. Two cultivars were identified for the rice–ratoon-rice system in cool-temperate environments of mid-latitudes. Improvement of ratooning ability of rice should be targeted by thorough evaluation of germplasms to increase ratoon rice yield in cool-temperate environments.

中文翻译：

---

日本中部冷温带环境再生稻农艺性能的基因型差异


冷温带环境下稻-再生稻系统面临的主要挑战是确保主要水稻作物收获后残茬的高再生能力。选择具有高再生能力的本地适应品种对于该系统至关重要。我们的目的是在日本中部（北纬 35° 至 36°N）（代表再生稻作物种植的北限）鉴定具有高再生稻产量的现代超短期品种，并阐明相关的生长特性。我们于 2019 年评估了 15 个超短期栽培品种（13 和 2 个），2020 年评估了 8 个（7 和 1 个），2021 年评估了 3 个（全部）在日本东京的水稻-再生稻系统中。再生稻产量与主稻产量在任何年份均不呈负相关。而分蘖再生率（再生稻季分蘖数与主季穗数之比）与再生稻产量呈极显着正相关。与这些品种相比，这些品种（“TNAU6484”和“ADT30”）的分蘖再生率和再生稻产量均较低。两个品种（“秋小町”和“一番星”）的分蘖再生率和再生稻产量最高。茎非结构碳水化合物浓度与主要水稻作物收获时宿根芽长度呈正相关。我们发现品种之间的再生能力存在显着差异。主要水稻作物收获时茎中积累的非结构碳水化合物可能有助于日本中部再生稻作物更快、更大的生长。尽管茎和籽粒之间存在光合作用竞争，但这种生长特征并不一定会降低超短栽培品种中主要水稻作物的产量。 鉴定出两个适合中纬度寒温带环境水稻-再生稻系统的品种。应以提高水稻再生能力为目标，深入开展种质资源评价，提高寒温带环境下再生稻产量。