Introgression lines of wild rice species and African cultivated rice

Interspecific hybridization offers an attractive way of enlarging the genetic diversity for crop improvement. Indeed, the genetic diversity found in wild species is often much larger that in their cultivated version. These resources are known to contain many interesting traits for breeding, including good to strong tolerance to abiotic and biotic stresses and various nutritional traits of interest (Sun et al 2001). In the framework of a Generation Challenge programme-funded project, we developed several libraries of introgression lines that carry genome fragments from Oryza spp. wild species and African cultivated rice O. glaberrima. This work was done in collaboration with Dr. Susan McCouch (Cornell University, NY), Embrapa-CNPAF (Brazil) and AfricaRice (Benin).
The first library consisted in a set of 64 introgression lines (or CSSLs) carrying contiguous chromosomal segments of O. glaberrima MG12 (acc. IRGC103544) in the genetic background of O. sativa ssp. tropical japonica (cv. Caiapó). Well-distributed SSR markers were used to characterize the introgression events. Average size of the substituted chromosomal segments in the substitution lines was about 10 cM and covered the whole donor genome, except for small regions on chromosome 2 and 4. Strong segregation distortion was found on chromosome 6, reflecting the selfish action of interspecific sterility gene S1 (see above). Recently, we undertook a GBS characterization of this population in collaboration with Yale University (unpublished data). This led us to a very dense genotyping with 15,000 SNPs, allowing a 26 kb-resolution of recombination breakpoints in each line. The three other libraries were obtained from hybridization between the tropical japonica accession Curinga from Brazil, and the wild species O. rufipogon, O. glumaepatula and O. meridionalis. They are available upon request to the corresponding author of this article. It is worth noting that the OMAP project leaded by Dr. Rod Wing (University of Arizona, AR) prepared BAC libraries and determined genome sequences for several of the donor accessions of our introgression lines (Ammiraju et al 2010; Liakat et al 2010).