Retrospective and perspective on indica three-line hybrid rice breeding research in China

Abstract

China's first indica hybrid rice technology has opened up new methods to substantially increase rice yield, tremendously contributing to China's food security. In this article, we review the discovery of wild abortive male sterility in rice and the history of the development and combination of the male sterile line, maintainer line and restorer line (the "three-line"). With regards to China's large-scale application of cytoplasmic-nuclear male-sterile (CMS) lines, in addition to the wild-abortive CMS line, there are also Gang, D, Yinshui, dwarf-abortive, Honglian and K types, of which, only the Honglian type exhibits a different restoring and maintaining relationship from that of the wild-abortive line. The diversity of cytoplasmic sterile lines of hybrid rice solves the potential risk in production caused by the use of a single cytoplasmic line. With respect to the breeding of elite parents, the breeding and application of fine male sterile lines, such as Zhenshan 97A, V20A, II-32A and Jin 23A, and fine restorer lines, such as IR24, Minghui 63 and Shuhui 527, were introduced. Currently, the major varieties of China's three-line hybrid rice have transformed from the high-yielding varieties in the past into the current high-quality, high-yield and disease-resistant varieties. However, three-line hybrid rice faces several problems, such as slow increases of yield potential, low efficiency in genetic improvement of maintainers, the high cost of hybrid rice seed production and the lack of adaptability to the simplified cultivation method. To meet these challenges, it is recommended to establish objectives of breeding new hybrid rice varieties with high quality, high yield, high safety and high efficiency by applying molecular tools to hybrid rice breeding and developing "three-line" hybrid rice parents suitable for mechanized seed production. These would significantly enhance the technological competitiveness of hybrid rice.