Resynthesized Brassica carinata is meiotically unstable but recovers fertility and meiotic stability following crossing to established B. carinata

Newly formed polyploids often face the challenge of genomic instability, which is usually observed as abnormal meiotic chromosome behaviour and poor fertility. However, the parental diploids of newly formed polyploids, as well as natural or evolved versions of the same polyploids, have usually adapted to these challenges and show regular meiosis and fertility. In this study, we assessed fertility and meiotic chromosome behaviour in established Brassica carinata , resynthesized B. carinata resulting from crosses between parental diploid species B. nigra and B. oleracea , and hybrids generated between these established and resynthesized B . carinata (resynthesized hybrids) using a combination of fertility estimates (seeds generated per pod, total seed set, and percentage pollen viability), and classical and molecular cytogenetic techniques. Cytological analysis revealed an expected chromosome number of 2 n  = 34 in the established B . carinata lines, whereas the resynthesized lines had 1–2 missing chromosomes. Fluorescent in situ hybridisation revealed that the B . nigra -contributed subgenome of B. carinata was more prone to chromosome loss. Hybridisation between the established and resynthesized B . carinata lines resulted in an improvement in fertility and meiotic behaviour in comparison to the pure resynthesized lines. Also, meiotic chromosome behaviour and fertility in the resynthesized hybrids showed an improvement across generations, implying a combination of hybridisation with an established polyploid and cultivation over generations may hasten genomic stability in newly synthesized polyploid lineages.