Stable, fertile lines produced by hybridization between allotetraploids <i>Brassica juncea</i> (AABB) and <i>Brassica carinata</i> (BBCC) have merged the A and C genomes
Elvis Katche, Roman Gaebelein, Zurianti Idris, Paula Vasquez‐Teuber, Yu‐tzu Lo, David Nugent, Jacqueline Batley, Annaliese S. Mason
Abstract
Summary Many flowering plant taxa contain allopolyploids that share one or more genomes in common. In the Brassica genus, crop species Brassica juncea and Brassica carinata share the B genome, with 2 n = AABB and 2 n = BBCC genome complements, respectively. Hybridization results in 2 n = BBAC hybrids, but the fate of these hybrids over generations of self‐pollination has never been reported. We produced and characterized B. juncea × B. carinata (2 n = BBAC) interspecific hybrids over six generations of self‐pollination under selection for high fertility using a combination of genotyping, fertility phenotyping, and cytogenetics techniques. Meiotic pairing behaviour improved from 68% bivalents in the F 1 to 98% in the S 5 /S 6 generations, and initially low hybrid fertility also increased to parent species levels. The S 5 /S 6 hybrids contained an intact B genome (16 chromosomes) plus a new, stable A/C genome (18–20 chromosomes) resulting from recombination and restructuring of A and C‐genome chromosomes. Our results provide the first experimental evidence that two genomes can come together to form a new, restructured genome in hybridization events between two allotetraploid species that share a common genome. This mechanism should be considered in interpreting phylogenies in taxa with multiple allopolyploid species.