Abstract Heterosis has helped to increase rice yield in F 1 hybrids by 15–20% beyond the level of inbred semi- dwarf varieties. For stable yield performance rice hybrids must also possess genetic resistance to biotic stresses. One of these, stem borer, reduces the expected yield of hybrid rice. The truncated synthetic cryIA(b) gene from Bacillus thuringiensis is known to be effective in controlling stem borer. The development of transformation techniques has provided the technology for incorporating this bacterial gene into the rice genome, which has not been possible by conventional breeding methods. We have introduced a new approach of using a transgenic maintainer line for devel- oping an insect-resistant hybrid rice. An elite IRRI main- tainer line (IR68899B) has been transformed with the cryIA(b) gene driven by the 35S constitutive promoter using the biolistic method. The integration and expression of the cryIA(b) gene could be demonstrated through South- ern and Western blot analyses that have been carried out so far up to the T 2 generations. Insect bioassay data showed an enhanced resistance to yellow stem borer in the Bt + transgenic plants. This is the first report of the develop- ment of a transgenic maintainer line for use in hybrid rice improvement. Key words Transgenic maintainer line · cryIA(b) gene · Insect resistant · Hybrid rice Abbreviations 2,4-D 2,4-Dichlorophenoxy acetic acid · NAA 1-α naphthalene acetic acid · Hg r hygromycin re- sistant Introduction Hybrid rice lines have been observed to produce 15–20% higher yields than inbred semidwarf varieties. Currently, rice hybrids are cultivated in about 55% of the rice-grow- ing areas of China and contribute 66% of the total rice pro- duction of the country. During the last 4 years, India and Vietnam have applied hybrid rice technology, and both plan to cover about 2.5 million hectare by 2000 A. D. (Virmani 1996). The cytoplasmic genetic male sterility system was found to be most effective for breeding rice hybrids. The production of hybrid rice involves three-line systems: cy- toplasmic male sterile (CMS), maintainer and restorer lines. Among the three lines, CMS has the most narrow ge- netic base (Virmani 1996). Incorporation of resistance gene(s) in a CMS line makes it widely applicable to the development of resistant rice hybrids. Since a CMS line is maintained by backcrossing to its isogenic maintainer line, the presence of resistance gene(s) in the latter will lead to the development of a CMS line possessing these genes. Stem borer is a serious problem for both inbred and hybrid rice. The available rice germplasm has a low level of resistance to yellow stem borer (YSB). Fortunately, Bt gene(s) from Bacillus thuringiensis offer enormous poten- tial to enhancing resistance to this pest. The crystal pro- tein or δ-endotoxin from B. thuringiensis has been found to be effective in controlling lepidopteran insects, includ- ing stem borer (Höfte and Whiteley 1989). Transformation of a maintainer line with a Bt gene would be useful when breeding CMS lines possessing this gene, which, in turn, would help in developing rice hybrids conferring resis- tance to stem borer. A number of crop plants such as to- bacco (Vaeck et al. 1987), maize (Koziel et al. 1993), to- mato (Delannay et al. 1989), cotton (Perlak et al. 1990) and soybean (Stewart et al. 1996) have been transformed with the Bt [cryIA(b)/cryIA(c)] gene and have subsequently shown resistance to stem borer. The earlier reported Bt-rice for inbred semidwarf va- rieties (Fujimoto et al. 1993; Wünn et al. 1996; Nayak et al. 1997; Wu et al. 1997) can not be used directly for de- Plant Cell Reports (1999) 18: 572–575 © Springer-Verlag 1999 Received: 17 December 1997 / Revision received: 23 June 1998 / Accepted: 25 September 1998 M. F. Alam · K. Datta · E. Abrigo · N. Oliva · J. Tu S. S. Virmani · S. K. Datta Transgenic insect-resistant maintainer line (IR68899B) for improvement of hybrid rice Communicated by G. Phillips M. F. Alam · K. Datta · E. Abrigo · N. Oliva · J. Tu S. S. Virmani · S. K. Datta () Plant Breeding, Genetics and Biochemistry Division, P. O. Box 3217, MCPO, 1271 Makati City, Philippines Fax no: (63-2) 8911292, 8178470 e-mail: SDATTA@IRRI.CGIAR.ORG