Advances in hybrid rice research and development in the tropics

During the past five years, hybrid rice technology in the tropics has entered the commercialization phase in India, Vietnam, the Philippines, Bangladesh, and Indonesia. Almost all the commercial rice hybrids are derived from the cytoplasmic male sterile (CMS) system. An IRRI CMS line, IR58025A, has been widely used in the tropics. Even in China, this line has been used in Jiangxi and Hunan provinces to improve the grain quality of local hybrids. IRRI's hybrid rice breeding program has focused on developing improved CMS lines possessing cytoplasmic and genetic diversity, improved grain quality, a higher outcrossing rate, and resistance to diseases and insects. Most widely used wild abortive cytoplasm has been analyzed for its effect on grain quality and resistance to/tolerance of biotic and abiotic stresses. There was no negative effect on the traits except for grain chalkiness, which needs to be studied further. As reported earlier, there was no lack of restorer lines among elite indica lines bred in the tropics. Marker-aided selection (MAS) using the sequence-tagged sire marker RG140 with Pvull digestion linked with the Rf3 gene on chromosome 1 was useful for increasing screening efficiency for restorers. Progress was also made in developing stable TGMS lines possessing a low critical sterility point and good outcrossing. Several public and private hybrids were released in national agricultural research and extension systems and new elite hybrids were identified. Average seed yields were further improved in the national programs by further fine-tuning of the seed production technology, training, the choice of appropriate locations/seasons, and, above all, the experience of seed growers. A significant increase occurred in private-sector participation in the hybrid rice seed industry during the past five years. About 40 private companies are actively involved in hybrid rice research and/or seed production and marketing in tropical Asia. During 2001, private companies were producing 90% of the hybrid rice seeds in India. Hybrid rice in the tropics covered about 770,000 ha in 2002. Major constraints identified during the commercialization phase of the technology in the tropics were inconsistent performance, inferior grain quality, an inadequate level of disease/insect resistance of hybrids, the inadequate supply and high cost of hybrid seeds, and inadequate policy support. Future opprotunities include the development of hybrids possessing stronger heterosis and more stable yield performance, improved grain quality, an adequate level of disease/insect resistance, and higher seed yields. Both conventional and molecular methods will be used in hybrid breeding and in assessing seed purity. Agronomic management of hybrid rice in the tropics will also be improved to improve hybrid yield and stability in performance. Hybrid rice, which made a significant impact in China in the 20th century, should contribute significantly to food security and environmental protection in the tropical rice-growing countries in the 21st century.