Intersubgenomic heterosis in rapeseed production with a partial new-typed Brassica napus containing subgenome A(r) firom B. rapa and C-c from Brassica carinata

A breeding strategy for utilizing intersubgenomic heterosis in rapeseed (Brassica spp.) was proposed by partially replacing the A(n) and C-n subgenomes of B. napus L. (A(n)A(n)C(n)C(n)) with the A(r) subgenome of B. rapa L. (A(r)A(r)) and Cc of B. carinata A. Braun ((BBCCc)-B-c-C-c-C-c), respectively. To replace the subgenomes of natural B. napus (A(n)A(n)C(n)C(n),), pentaploid hybrids were first produced by mating the synthetic hexaploid (A(r)A(r)B(c)B(c)C(c)C(c)) with natural B. napus. Progenies of pentaploid hybrids were considered as the partial new-typed B. napus (A(r)A(r)C(c)C(c)) since they contained 38 chromosomes and half of their genome was introgressed from A(r)/C-c subgenome based on cytological and molecular assay. Most individuals of the partial new-typed B. napus showed normal meiotic behavior, high portion of germinated-pollen and good seed set. Intersubgenomic hybrids were produced by crossing cultivars of natural B. napus with the partial new-typed B. napus plants selected from F-3, F-4, and F-5 generations. Seed yield potential of intersubgenomic hybrids was tested for three successive years and most hybrids showed strong over-control or midparent heterosis. Seed yield of hybrids was positively correlated with the genomic proportion of A(r), C-c and A(r) + C-c in the new-typed B. napus. It is suggested that increasing the subgenomic portion of A(r)/C-c in the new-typed B. napus might further strengthen the intersubgenomic heterosis for seed yield.