Key message: AllohexaploidBrassicapopulations reveal ongoing segregation for fertility, while genotype influences fertility and meiotic stability. Abstract: Creation of a new Brassica allohexaploid species is of interest for the development of a crop type with increased heterosis and adaptability. At present, no naturally occurring, meiotically stable Brassica allohexaploid exists, with little data available on chromosome behaviour and meiotic control in allohexaploid germplasm. In this study, 100 plants from the cross B. carinata × B. rapa (A2 allohexaploid population) and 69 plants from the cross (B. napus × B. carinata) × B. juncea (H2 allohexaploid population) were assessed for fertility and meiotic behaviour. Estimated pollen viability, self-pollinated seed set, number of seeds on the main shoot, number of pods on the main shoot, seeds per ten pods and plant height were measured for both the A2 and H2 populations and for a set of reference control cultivars. The H2 population had high segregation for pollen viability and meiotic stability, while the A2 population was characterised by low pollen fertility and a high level of chromosome loss. Both populations were taller, but had lower average fertility trait values than the control cultivar samples. The study also characterises fertility and meiotic chromosome behaviour in genotypes and progeny sets in heterozygous allotetraploid Brassica derived lines, and indicates that genotypes of the parents and H1 hybrids are affecting chromosome pairing and fertility phenotypes in the H2 population. The identification and characterisation of factors influencing stability in novel allohexaploid Brassica populations will assist in the development of this as a new crop species for food and agricultural benefit.