Abstract: By testing the germination speed, seedling emergence rate, coleoptile node length and mesocotyl length of cultivated rice varieties at different treatments of soil depth (2 cm, 4 cm and 6 cm) during germination, the germinating dynamic source of rice was studied. Germinating dynamics in rice mostly came from the elongation of coleoptile node and mesocotyl, and there were obvious differences among different rice germplasms under different resistance conditions. At 2 cm soil depth, the germination speed and seedling emergence rate of cultivated rice varieties were similar to the germination rate indoors. Long mesocotyl varieties had high germination speed and normal seedling emergence rate at 4 cm or 6 cm soil depth, whereas the short mesocotyl ones contrarily, e.g. the seedling emergence rate of Chunjiang 683 were decreased by 6.5 and 86.2 percent points compared with germination rate indoors, respectively. It was also indicated that the elongation of mesocotyl played a key role in rice germination at 4 cm and 6 cm soil depth. The long mesocotyl rice germplasms had strong germinating dynamics, which mostly came from the action of coleoptile and mesocotyl together; whereas the short mesocotyl germplasms had poor germinating dynamics which only came from the elongation of coleoptile. Using the long mesocotyl germplasm to solve the problem of lodging and germination rate in direct-seeded rice production was also discussed.

Key words: rice, direct-seeded rice, mesocotyl, germination rate, seedling emergence rate, dynamics

摘要： 在自然条件下，通过设计不同的出苗阻力（覆土深度2 cm、4 cm和6 cm）来测定中胚轴伸长潜力不同的水稻种质的出苗速度、成苗率和芽鞘节及中胚轴的长度，以分析影响水稻种子顶土出苗的动力源。结果表明，水稻种子的出苗动力主要来源于芽鞘节间和中胚轴的伸长。在不同阻力处理条件下，不同种质出苗动力差异较大，其中覆土2 cm的不同种质出苗率相差不明显，与室内发芽率结果比较接近，覆土4 cm和覆土6 cm的两个处理不同种质间出苗率差异明显，长胚轴种质出苗速度快，出苗率高，出苗率与室内发芽率相差不大；而短胚轴种质出苗速度慢，出苗率低，其中春江683的出苗率与室内发芽率相比分别下降了6.5和86.2个百分点。研究表明水稻中胚轴的伸长对覆土较深的种子顶土出苗起到关键作用，长胚轴种质顶土出苗动力来自于芽鞘节与中胚轴的共同作用，出苗动力强；而短胚轴顶土出苗动力主要来源于芽鞘节的伸长，出苗动力较弱。还对通过选育长胚轴直播稻品种解决直播稻易倒伏和出苗差等难题的可能性进行了探讨。

关键词: 水稻, 直播稻, 中胚轴, 发芽率, 出苗率