Pyramiding of insect- and disease-resistance genes into an elite indica, cytoplasm male sterile restorer line of rice, 'Minghui 63'

The wild-rice-derived dominant gene Xa21 conferring multi-race resistance to bacterial blight and a fused Bt gene cry1Ab/cry1Ac conferring resistance to lepidopteran insects were individually introduced into the same genetic background of an elite indica cytoplasm male sterile (CMS) restorer line 'Minghui 63'. The line showed the desirable insect- and disease-resistant phenotypes. To maximize the effect, the two genes were also pyramided into the same recipient plant of 'Minghui 63' by marker-assisted selection. After being subjected to natural infestation of leaf-folders and yellow stem borers and inoculation of Xoo strain mixtures, the pyramiding line and its derived hybrids showed high levels of resistance against both insect damage and disease. Furthermore, data from field trials demonstrated that the hybrids made by crossing this pyramiding line with the CMS lines 'Zhenshan 97A' and 'Maxie A' retained a similar level of yield under conditions without chemical spray, indicating that the pyramiding genes have a yield-stabilizing effect on the recipient line and its hybrids.