Research Progress of Speed Breeding Technology in Rice (Orysa sativa L.)

Rice (Orysa sativa L.) is one of the most important food crops in China, playing a major role in guaranteeing food security. Thanks to the development of science and technology, especially the progress of rice breeding technology, there have been two rounds of substantial increase in China's rice yield since the large-scale application of dwarf rice breeding and hybrid rice technology. Consumer demand for rice varieties and rice products is becoming increasingly diversified in the new era, and the current efficiency of rice breeding is still not satisfactory enough to meet future demand. As a self-pollinated crop, rice requires multiple generations of continuous self-crossing to achieve genetic homozygosis and stability in segregating generations during the breeding process. However, the long growth cycle of rice in paddy field and the difficulty of year-round planting have led to a long breeding cycle, which has become one of the crucial bottlenecks in rice breeding. Speed breeding is a new technology rising in recent years that promotes crop growth, flowering and maturation through comprehensive measures such as environmental regulation and growth manipulation to expedite the crop generation advance, which can shorten the "seed to seed" cycle and realize multi-generation breeding annually, and promises to significantly shorten the breeding cycle and improve the breeding efficiency. In this review, we focus on the rice crop and systematically describe the research status and progresses of speed breeding in rice in terms of the rise of crop speed breeding technology, the research overview of rice speed breeding, key genes in rice speed breeding, environmental factors affecting the rice flowering and maturation, and the incorporation of speed breeding and modern breeding technology. Further, we discuss and look forward to the challenges and key directions of future research in this field, aiming to promote the rapid development and application of speed breeding technology in rice, improve the efficiency of rice breeding, and provide useful references for guaranteeing food security and sustainable development of agriculture.