Allopolyploids often exhibit advantages in vigor and adaptability compared to diploids. A long-term goal in the economically important Brassica genus has been to develop a new allohexaploid crop type (AABBCC) by combining different diploid and allotetraploid crop species. However, early-generation allohexaploids often face challenges like unstable meiosis and low fertility, and the phenotypic performance of these synthetic lines has rarely been assessed. This study analyzes agronomic traits, fertility, and genome stability in A