Prof. Yuan devoted his whole life to the research of hybrid rice. On the first anniversary of Prof. Yuan Yuan’s death, our research team wrote a paper to commemorate him. In this paper, we recalled his life, his research progress and achievements of hybrid rice. He led and guided his research team to overcome difficulties in hybrid rice research. Hybrid rice has made important contributions to China and world’s food security. He is a great researcher worthy of our memory forever in the world.

Increasing rice production by using genetically improved rice cultivars and fertilizer application has been the main objective of rice farming. The double rice-cropping system has been an important rice production system in the middle and lower reaches of the Yangtze River in China since the 1950s. It is of great significance to determine whether hybrid vigor can make a substantial contribution to early- and late-season rice production, and how the heterosis expression of hybrid rice functions under different level of fertilization application. The objective of this study was to evaluate the grain yield and associated plant traits of popular hybrid and inbred rice varieties with large-scale promotion under conditions of customary (high) and combined (low) fertilization in the early and late seasons of 2017-18 in Changsha County, Hunan Province, central Southern China. We found that hybrid rice varieties displayed their respective advantages in the early- and late-rice seasons, but the advantages in their relative yield traits varied. The main advantages of early-season rice were effective panicle number per hill (EPN), 1000-grain weight (KGW), harvest index (HI), yield, and nitrogen use efficiency (NUE). Whereas in late-season rice, the major advantages were grain number per panicle (GNP), HI, yield, and NUE. The EPN was the main advantage of early-season hybrid rice with a short-growth period, and the GNP was the main advantage of late-season hybrid rice with a long-growth period. The main yield advantage of hybrid rice was stronger under combined (low) fertilization than under customary (high) fertilization. Hence, high yield can be achieved by selecting good hybrid rice varieties and by using combined fertilization (lower fertilizer use with higher efficiency). This work is contributive for rice growers, extension specialists, and fertilizer producers, as it provides data that can be used to maximize yields with reduced fertilizer and pesticide inputs.