Microspore culture preferentially selects unreduced (2n) gametes from an interspecific hybrid of Brassica napus L. x Brassica carinata Braun

We analysed the products of male meiosis in microspore-derived progeny from a Brassica napus (AAC(n)C(n)) x Brassica carinata ((BBCCc)-C-c) interspecific hybrid (ABC(n)C(c)). Genotyping at 102 microsatellite marker loci and nuclear DNA contents provided strong evidence that 26 of the 28 progeny (93%) were derived from unreduced (2n) gametes. The high level of (CCc)-C-n marker heterozygosity, and parallel spindles at Anaphase II in the ABC(n)C(c) hybrid, indicated that unreduced gametes were formed by first division restitution. The frequency of dyads at the tetrad stage of pollen development (2.6%) suggested that unreduced gametes were preferentially selected in microspore culture. Segregation of marker alleles in the microspore-derived progeny was consistent with homologous recombination between C-n and C-c chromosomes and homoeologous recombination involving A-, B- and C-genome chromosomes during meiosis in the ABC(n)C(c) hybrid. We discuss the potential for using microspore culture of unreduced gametes in interspecific hybrids to map Brassica centromeres through half-tetrad analysis.