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 Irrigated Rice Research Consortium
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Elite CMS lines for the tropics
Several public- and private-sector hybrid rice breeding institutions around the world have been recipients of the products of their breeding work. After a thorough evaluation by the national seed boards, some of these experimental hybrids have been released to farmers as new hybrid varieties for cultivation. Some parental lines have been used in combination with local varieties to develop experimental hybrids, a number of which have been released to farmers as new hybrids. The following sections describe the traits of four elite cytoplasmic male sterile (CMS) lines that are considered to be the most promising among the CMS lines that the group has developed. IR58025A and IR58025B IR58025A is the result of a cross between IR48483A (Zhen Shan 97A/6*MR 365) and Pusa 167-120-3-2. Zhen Shan 97A is a male sterile line originally developed in China, whereas MR365 and Pusa 167-120-3-2 are elite lines from India. The initial testcross was made in the 1982 wet season (WS) and was followed by eight successive backcrosses in which only backcross progenies with 100% pollen sterility were selected and advanced. The line was designated in 1987 as IR58025A. IR58025A possesses wild abortive (WA) cytoplasm and has 99.9% pollen sterility. It has been observed to have 40–45% seed set because of outcrossing under a high pollen supply. It is semidwarf in stature and flowers in about 90 days after seeding in wetbed conditions. IR58025A grows about 90–95 cm high and produces about 14 tillers. It has a panicle length of about 21 cm and around 200 spikelets per panicle. IR58025A is a good combiner such that it gives many heterotic combinations when crossed with restorer lines. In testcross nurseries observed from 1988 to 1990, on average, about 44% of all testcrosses showed normal fertility and several were heterotic. Hybrids have been developed with this CMS line both at IRRI and in some national hybrid rice breeding institutions (including private-sector programs). National programs of India, Vietnam, the Philippines, Bangladesh, and Indonesia have released some of these hybrids. Among these is the IRRI-bred hybrid IR68284H that was released in the Philippines in 1997. Popularly known as Mestizo 1, this hybrid presently occupies a majority of the area planted to hybrid rice in the Philippines. |
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