Rice Genomics and Genetics 2025, Vol.16, No.4, 180-198 http://cropscipublisher.com/index.php/rgg 185 3.3 1000-grain weight and yield comparison The thousand-grain weight reflects the fullness and size of rice grains and is one of the important factors affecting yield. The thousand-grain weight of the new varieties demonstrated this time is generally between 25 and 29 grams, and there is little difference between varieties. The thousand-grain weight of "Yongyou 33" is about 26.6 grams, and that of "Jiangliangyou 7901" is about 26.3 grams; the conventional rice "Xiushui 1717" is 25.7 grams, and that of "Jiahe 567" is 27.3 grams; the control "Xiushui 134" has a thousand-grain weight of 27.7 grams. It can be seen that the grain size of the new varieties is generally comparable to that of the traditional varieties, some are slightly higher than the control, and some are slightly lower, but the difference does not exceed ±10%. This shows that the new varieties mainly increase yield by increasing the number of panicles and the fruiting rate, rather than simply increasing the grain size. In fact, too large grains may reduce the fruiting rate, while too small grains affect the thousand-grain weight. The relationship between grain weight and grain number needs to be weighed in breeding. In terms of actual yield, the new varieties have increased yields to varying degrees compared with the control varieties. In the plot display test, "Xiushui 134" was used as the conventional rice control and "Yongyou 1540" was used as the hybrid rice control. It can be found that the yields of most new varieties exceeded the control. For example, "Xiushui 1717" increased its yield by 5.8% compared with the control, and "Jiahe 567" increased its yield by 15.0%; the hybrid rice "Yongyou 33" increased its yield by 3.7% compared with the control, showing high and stable yields. New varieties such as "Chunjiang 204" increased their yield by 6.9%, following closely behind. Only a few varieties such as "Zhejing 100" and "Zhehujing 58" had slightly lower yields than the control (a reduction of about 10%), indicating that they are not adapted to the climatic conditions in this region. In large-scale demonstrations, the average yield of new indica-japonica hybrid rice varieties was about 780 kilograms per mu, and the yield of conventional late japonica rice was about 600-650 kilograms per mu. Hybrid rice varieties have significantly improved their yield levels with their greater biological yield and hybrid vigor, and their yield per mu is about 15%-20% higher than that of conventional rice. This result is basically consistent with the increase in hybrid rice yield across the country. It is generally believed that the increase in hybrid rice yield over conventional rice can reach 10%-20%. For example, in the double-season rice high-yield research field in Hunan, the double-season hybrid rice yield per mu reached more than 1 530 kilograms, setting a new record. The yield of hybrid rice such as "Yongyou 33" exceeded 550 kilograms per mu, while the conventional rice control was 627.4 kilograms per mu. If the difference in growth period is taken into account, the high-yield potential of late hybrid rice can be seen. Of course, conventional late japonica rice varieties have also been improved, and their yield levels have also been greatly improved. For example, "Jiahe 567" performed outstandingly among conventional rice varieties, with an acreage yield of 721.5 kg, which is significantly better than traditional varieties. While maintaining the high-quality rice standard in thousand-grain weight, the new variety significantly increased the actual yield by increasing the number of panicles and the fruiting rate. This shows that breeders have successfully achieved a combination of high yield and high quality while maintaining the quality of rice (Huang et al., 2024). Academician Yuan Longping also pointed out that high yield and quality are not irreconcilable contradictions, and hybrid rice can achieve improvements in both yield and quality at the same time. 4 Evaluation of Physiological Resistance and Stress Adaptability 4.1 Resistance to pests and diseases Pest and disease resistance is a key factor in whether new varieties can stably exert their yield-increasing potential. The new rice varieties demonstrated this time have relatively good disease and pest resistance overall, but there are certain differences between different varieties. For the main disease rice blast, many new varieties show a medium resistance level. For example, "Jiahe 567" was identified as having a maximum loss rate of 3 levels for panicle neck blast and a comprehensive resistance index of 3.0 for rice blast, which is a medium resistance to rice blast; "Xiushui 1926" also showed medium resistance to rice blast, and no obvious lesions were found in the field. In contrast, most new varieties have average resistance to the bacterial disease rice bacterial leaf blight, such as Jiahe 567, which has a maximum resistance of 5 levels to bacterial leaf blight, which is a medium level of sensitivity. This suggests that attention should be paid to the prevention of bacterial leaf blight in rainy and hot
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