Exploring the Power of Rice (O. sativa x O. rufipogon) Chromosome Segment Substitution Line Libraries.

Transgressive variation was reported as an increase in grain yield for several rice (Oryza sativa x O. rufipogon) advanced backcross mapping populations. The objective of this study was to develop chromosome segment substitution line (CSSL) libraries to further dissect the reported transgressive variation with these mapping populations. Six CSSL libraries were developed by crossing two adapted rice varieties, IR64 (subspecies indica) and Cybonnet (subspecies japonica), as recurrent parents to three accessions of the wild rice ancestral species, O. rufipogon, as donor parents. Two accessions clustered with O. sativa representing the subspecies indica (IRGC106148) and japonica (W1944), whereas the third (IRGC105567) clustered with several with O. rufipogon accessions. SNP markers were part of the marker assisted backcrossing method used to select the individual pre-CSSLs which were advanced each generation based on the targeted wild segments. Each of the final CSSL libraries has 81 to 90 lines, with each line having 4-5MB of a targeted wild donor introgression and 95-100% recurrent parent background. Genotyping by Sequencing was used for the final CSSL selections, thus providing a high density of polymorphic SNP markers which can be used for fine mapping. Collectively, the set of CSSLs for a given library represents the entire genome of the wild donor parent in the background of either IR64 or Cybonnet. The usefulness of CSSL libraries for identifying genes underlying agronomically important traits will be demonstrated with segregating F₂ lines derived from selected heterozygous pre-CSSLs segregating for certain target segments. In the future, we will use these CSSL libraries to understand the genetic basis of transgressive variation, identify novel genes or alleles contributed by the wild donor, characterize genetic interactions between wild donor and divergent elite cultivated background, and broaden the gene pool of cultivated rice.