Genetic basis of heterosis in two rice hybrids.
1994
Mao C.X. | Virmani S.S.
Six basic generations (P1, P2, F1, F2, B1 and B2) and triple test cross families of the heterotic rice hybrids IR46830 B/IR9761-19-1 R and IR54752 B/IR 46R were developed and tested in an experiment using completely randomized design at IRRI in 1991 DS to investigate the genetic basis of heterosis. Nine agronomic traits (grain yield, dry matter weight, 100-grain weight, tiller number, panicle number, spikelet number, plant height, days to heading, and harvest index) were studied and data were analyzed using biometric models (joint scaling test, three-and six-parameter model, perfect fit solution, and triple testcross analysis). In cross 2, F2 was substituted by F3 because the F2 mean was found to be lower than the lower parent. Significant heterosis was observed for grain yield, dry matter weight, and 100-grain weight in the cross IR46830 B/IR9761-19-1R; and for grain yield, dry matter weight, spikelet number, and days to heading in the cross IR54752 B/IR46 R. Other traits did not show significant heterosis. The dominance ratio for traits showing heterosis was greater than unity, but it was equal to or smaller than one for traits not showing heterosis. Traits showing heterosis showed significant additive and dominance effects in the cross IR46830 B/IR9761-19-1R, and not only significant dominance effects but also significant additive, additive, additive x dominance, and dominance x dominance effects in the cross IR54752 B/IR46 R. Triple test cross analysis showed pronounced additive, dominance, and epistatic variances controlling traits showing heterosis in the cross IR54752 B/IR46 R, and only additive and dominance variances in the cross IR46830 B/IR9761-19-1 R. Linkages were detected in the traits showing significant epistatis. In the absence of epistatis and linkages, the greater-than-1 dominance ratio in cross 1 indicated a certain degree of overdominance.
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