Chromosome instability of allopolyploid resynthesized Brassica napus

Allopolyploid resynthesized Brassica napus (AACC, 2n = 38) was produced by cross-hybridization between B. rapa (AA, 2n = 20) and B. oleracea (CC, 2n = 18) for new vegetative crop breeding. Many studies have provided evidences for the phenotype instability and close relationship between A and C genome in the amphidiploid resynthesized B. napus cultivars. In fact, a new B. napus varieties, Hanakkori showed atypical morphological characters and generated many off-type progeny plants. In this study, we investigated the pollen fertility, chromosome number, structure, and behavior linked to defi ne the factors, which produce the unstable phenotypic expressions in the Hanakkori progenies. We define the chromosome number and chromosome organization using fl uorescence in situ hybridization analysis on somatic mitosis and meiosis cells. Off-type plants with lower pollen fertility show the instability of chromosome number and structures with small chromosome fragments. Observation of chromosomes behaviors at meiosis showed that the meiotic division in off-type plants led to appreciably higher abnormalities than in on-type plants. These results demonstrated that minimized abnormal chromosome structure and formation might be essential to stabilize the normal progenies in the B. napus plant breed-