Rice Genomics and Genetics 2025, Vol.16, No.4, 180-198 http://cropscipublisher.com/index.php/rgg 184 "Jiahe 567" is about 96 cm. Higher plant height is conducive to the formation of a larger population leaf area and photosynthetic potential of hybrid rice, but it may also increase the risk of lodging. Conventional late japonica rice varieties such as "Xiushui 1717" have a plant height of about 102 cm, which is medium to short, and is relatively resistant to lodging. In terms of tillering, all varieties are planted by machine transplanting, with similar basic seedling density, but there are differences in the number of effective tillers. Hybrid rice varieties have vigorous individual growth and more tillers per plant, but some ineffective tillers are difficult to form ears in the later stage; conventional rice varieties have medium tillering ability, good population uniformity, and often higher ear formation rate. Field surveys show that the highest number of seedlings per mu of "Yongyou 33" reached 1.73 million, 210 000 ears/mu, and an ear formation rate of about 68.4%; the highest number of seedlings of "Xiushui 1717" was about 3.07 million, 150 400 ears, and an ear formation rate of 68.4%. The highest number of seedlings of "Jiahe 567" was 3.02 million, 202 000 ears, and an ear formation rate of 66.9%. It can be seen that the ear formation rate of different varieties ranges from about 65% to 70%. High-yield varieties often maintain a higher ear formation rate, which is related to the reasonable distribution of their tillers and the quality of the population. Zhou et al. (2020) pointed out that the panicle formation rate of high-yield, high-nitrogen and high-efficiency indica-japonica hybrid rice can be stabilized at 68%~70%, and the leaf area index is high during the heading period and decays slowly in the later period, which helps to increase the number of panicles in the group. Among the new varieties demonstrated this time, "Yongyou 33" and "Xiushui 1717" all showed a high panicle formation rate and a large number of spikelets in the group, which laid the foundation for high yield. However, for hybrid rice varieties with high plant height and lush growth, it is necessary to be vigilant about the risk of lodging in the later period, and to reasonably plant densely and control the nitrogen fertilizer level to balance the growth of the group and the resistance to lodging. 3.2 Panicle traits and grain filling success Panicle traits directly determine the yield composition of rice, and new varieties have their own characteristics in panicle-grain structure and fruiting rate. New varieties of indica-japonica hybrid rice often have the advantage of "large panicle and many grains", and the total number of grains per panicle is significantly higher than that of conventional japonica rice varieties (Liu et al., 2023). For example, the average total number of grains per panicle of "Yongyou 33" is about 307, and that of "Jiangliangyou 7901" is about 280; in comparison, the total number of grains per panicle of "Xiushui 1717" is about 150, and that of "Jiahe 567" is about 143. Hybrid rice increases the number of grains per panicle through large panicles, thereby increasing the yield potential per plant. At the same time, most new varieties show a high fruiting rate. Demonstration survey data show that the fruiting rate of "Yongyou 33" is about 85.2%, and the fruiting rate of "Jiangliangyou 7901" is about 85%; the fruiting rate of conventional rice "Xiushui 1717" is 94.8%, and the fruiting rate of "Jiahe 567" is 94.3%. The fruiting rate of most new varieties is between 85% and 95%. The fruiting rate of conventional japonica rice is generally slightly higher than that of hybrid rice, which may be due to the moderate number of grains per panicle of conventional varieties and more complete filling, while some hybrid rice panicles have large grains and are prone to empty grains in unfavorable environments. However, the overall fruit setting rate of the demonstration varieties was ideal, and no serious empty and barren phenomenon occurred. Some varieties with poor performance, such as "Zhehangyou 220", had a fruit setting rate of only about 89%, fine grains in the ears, and limited yield increase potential. The "Yongyou" series of varieties have the advantages of large ears and high fruit setting rate, and the filling is uniform and consistent. The ears and grains in the "Yongyou 33" demonstration field are full, and although the fruit setting rate is slightly lower than that of some conventional rice, it still remains above 85% in high temperature years, showing good filling ability and adaptability to the environment. The high or low fruit setting rate reflects the reproductive growth intensity and tolerance to stress of the variety. High-yield varieties maintain a high fruit setting rate while having large ears and many grains, indicating that they have both sufficient assimilates and good resistance to stress filling. The new varieties demonstrated this time have obvious advantages in ear traits: indica-japonica hybrid rice increases yield by significantly increasing the number of grains per ear, while conventional japonica rice ensures a higher number of fruited grains with a higher fruit setting rate. The different panicle characteristics of the two types of varieties provide different ways to achieve high yields.
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