Introgressing Subgenome Components from and to for Broadening Its Genetic Base and Exploring Intersubgenomic Heterosis.

(AABB), is an allotetraploid that arose from two diploid species, (AA) and (BB). It is an old oilseed crop with unique favorable traits, but the genetic improvement on this species is limited. We developed an approach to broaden its genetic base within several generations by intensive selection. The A subgenome from the Asian oil crop (AA) and the B subgenome from the African oil crop (BBCC) were combined in a synthesized allohexaploid (AABBCC), which was crossed with traditional to generate pentaploid F hybrids (AABBC), with subsequent self-pollination to obtain newly synthesized (AA/BB/). After intensive cytological screening and phenotypic selection of fertility and agronomic traits, a population of new-type was obtained and was found to be genetically stable at the F generation. The new-type possesses good fertility and rich genetic diversity and is distinctly divergent but not isolated from traditional , as revealed by population genetic analysis with molecular markers. More than half of its genome was modified, showing exotic introgression and novel variation. In addition to the improvement in some traits of the new-type lines, a considerable potential for heterosis was observed in inter-subgenomic hybrids between new-type lines and traditional accessions. The new-type exhibited a stable chromosome number and a novel genome composition through multiple generations, providing insight into how to significantly broaden the genetic base of crops with subgenome introgression from their related species and the potential of exploring inter-subgenomic heterosis for hybrid breeding.